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1 - Optical imaging and magnetic field simulation of a DC circular planar magnetron sputtering discharge
Ahmad Rastkar Ali Reza Niknam Mostafa SalahshoorIn this paper, the optical images of glow discharge plasma and the finite element method simulation of the magnetic field strength in a balanced and two types of unbalanced DC circular planar magnetron sputtering sources are presented. The investigation showed that wher أکثرIn this paper, the optical images of glow discharge plasma and the finite element method simulation of the magnetic field strength in a balanced and two types of unbalanced DC circular planar magnetron sputtering sources are presented. The investigation showed that wherever the magnetic field strength is stronger, the intensity of light and the ionization are greater and consequently, the deposition is higher. The comparison of recorded optical images with the finite element simulation results of the magnetic field strength indicated the correlation between regions of high magnetic field strength and high light emission. تفاصيل المقالة -
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2 - Finite element formulation for the free vibration analysis of embedded double-walled carbon nanotubes based on nonlocal Timoshenko beam theory
Milad Hemmatnezhad Reza AnsariAbstractThe present paper is concerned with the free vibration analysis of double-walled carbon nanotubes embedded in an elastic medium and based on Eringen's nonlocal elasticity theory. The effects of the transverse shear deformation and rotary inertia are included acc أکثرAbstractThe present paper is concerned with the free vibration analysis of double-walled carbon nanotubes embedded in an elastic medium and based on Eringen's nonlocal elasticity theory. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The governing equations of motion which are coupled with each other via the van der Waals interlayer forces have been derived using Hamilton's principle. The thermal effect is also incorporated into the formulation. Using the statically exact beam element with displacement fields based on the first order shear deformation theory, the finite element method is employed to discretize the coupled governing equations which are then solved to find the natural frequencies. The effects of the small scale parameter, boundary conditions, thermal effect, changes in material constant of the surrounding elastic medium, and geometric parameters on the vibration characteristics are investigated. Furthermore, our analysis includes nonlocal double-walled carbon nanotubes with different boundary conditions between inner and outer tubes which seem to be scarcely considered in the literature, and the corresponding given results for this case can be considered as a benchmark for further studies. Comparison of the present numerical results with those from the open literature shows an excellent agreement. تفاصيل المقالة -
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3 - مطالعه تجزیه فتوکاتالیزوری رنگ‌زاهای راکتیو از پساب های نساجی: مدلسازی عددی اجزای محدود و کارهای تجربی
خشایار بدیعی فرامرز دولتی ارده‌جانی سید ضیاءالدین شفایی تنکابنی نیاز محمد محمودی فرخ‌لقا امینیپساب های محتوی رنگ‌زاهای راکتیو که ممکن است از صنایع مختلف تولید شود اثرات و پیامدهای زیست محیطی بسیاری به همراه دارد. از این رو بررسی امکان حذف این مواد رنگی از پساب‌ها قبل از تخلیه آن ها به محیط زیست اطراف از اهمیت اساسی برخوردار است. در این تحقیق یک مدل ساد أکثرپساب های محتوی رنگ‌زاهای راکتیو که ممکن است از صنایع مختلف تولید شود اثرات و پیامدهای زیست محیطی بسیاری به همراه دارد. از این رو بررسی امکان حذف این مواد رنگی از پساب‌ها قبل از تخلیه آن ها به محیط زیست اطراف از اهمیت اساسی برخوردار است. در این تحقیق یک مدل ساده ریاضی که به روش عددی اجزاء محدود بسط داده شده‌است، ارایه شده که قادر است فرآیند حذف مواد رنگی راکتیو را از پساب های صنعتی شبیه سازی نماید. مدل ریاضی ارایه شده توسط ترکیبی از نرم افزارهای SEEP/W و CTRN/W حل شده است. مدل ابتدا توسط یک مثال در مورد حمل یک ماده آلاینده در سیستم جریان آب در یک محیط متخلخل که به دو روش عددی و تحلیلی بررسی شده است، کالیبره شد. پس از کالیبراسیون مدل، نتایج حاصل از مدل‌سازی با نتایج به دست آمده از یک تحقیق در مقیاس آزمایشگاهی جهت حذف یک رنگ‌زای سیباکرونی راکتیو نارنجی 107 با فتوکاتالیز (UV/TiO2/H2O2) در یک راکتور ناپیوسته(Batch reactor) و همچنین با نتایج حاصل از حل تحلیلی مدل مقایسه شد و همپوشانی مناسبی به دست آمد. بررسی‌های تجربی نشان داد که رنگ‌زاهای سیباکرونی همچون رنگ‌زای راکتیو نارنجی 107 در اثر تابش فرابنفش و در حضور فتوکاتالیزور و عامل اکسید کننده همچون آب اکسیژنه کاملاً رنگ‌بری شده و به ترکیبات معدنی تبدیل می‌شوند. اگرچه تولید چنین پساب‌هایی توسط صنایع مختلف تقریباً اجتناب ناپذیر است، ولی با استفاده از نتایج حاصل از چنین شبیه‌سازی‌هایی می‌توان به طراحی مناسب برنامه‌های مدیریت زیست محیطی پساب‌های صنعتی به منظور به حداقل رساندن اثرات نامطلوب آن پرداخت. تفاصيل المقالة -
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4 - Analysis of the Free Edge Effect of a Composite Laminate under Axial Tensile Load According to the Environmental Properties of the Composite Materials
S Ebadi E AnbarzadehIn recent years, composites have been used to reduce the overall weight of the structure and reduce the consumption of fossil fuels in aircraft due to their light weight property. The purpose of this study is to investigate the interlayer stresses created in composite l أکثرIn recent years, composites have been used to reduce the overall weight of the structure and reduce the consumption of fossil fuels in aircraft due to their light weight property. The purpose of this study is to investigate the interlayer stresses created in composite layers due to the effect of free edges. In fact, in this study, the distribution of stresses affected by free edges (interlayer stresses) that create force and torque in the direction of thickness is investigated. For this purpose, the changes of the mentioned stresses with the help of numerical modeling for multilayer composite by finite element method are investigated by Abacus software and the environmental effects of composite materials are also discussed. Finally, the effect of different layers on this phenomenon in terms of thickness and width of several composite layers under axial tensile load will be investigated. As a result, on one hand the extended usage of green materials like composites can potentially reduce the previous heavy metallic structures which use more fuel and have much more environmental side effects, and on another hand some stress analytical results such as symmetrically distribution of , asymmetrically distribution of across the width of multilayer and other discoveries for angle-ply and quasi-isotropic multilayers due to the effect of free edge are gained. تفاصيل المقالة -
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5 - Simulation of Ultrasonic Welding of Al-Cu Dissimilar Metals for Battery Joining
Reza Abdi Behnagh Peyman Esmaeilzadeh Mohsen Agha Mohammad PourUltrasonic welding is gaining popularity for joining of thin and dissimilar materials and foils in the fabrication of automotive Li-ion battery packs because of excellent efficiency, high production rate, high welding quality, etc. Precise control of the parameters of t أکثرUltrasonic welding is gaining popularity for joining of thin and dissimilar materials and foils in the fabrication of automotive Li-ion battery packs because of excellent efficiency, high production rate, high welding quality, etc. Precise control of the parameters of the welding process plays an important role in achieving good joint quality. Numerical simulation can greatly help control the main input parameters such as frequency, clamping pressure, friction coefficient, and vibration amplitude. In this present work, a three-dimensional thermo-mechanical Finite Element (FE) model is proposed using ABAQUS/EXPLICIT for the dissimilar Al to Cu weld to predict the deformation and temperature as output parameters during welding process by varying input parameters. The simulation results showed that the clamping pressure, vibration frequency and friction coefficient have a great influence on heat production during the process which was critical to determine the final quality of the welded joint. Studies also showed that increased clamping force and welding frequency led to increased deformation. تفاصيل المقالة -
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6 - Evaluating the Effect of Operating Conditions on Temperature Variation Rate of Inner Walls and Inside Inflated Air of Pneumatic Tires
Moslem Namjoo Hossein Golbakhshi Farhad Khoshnam Ahmad SoleimaniFor rolling pneumatic tires, the thermal induced effects are mainly resulted from visco-elastic behaviour of rubber parts and dissipation of stores strain energy during the cyclic deformations. It is noted that the operating conditions crucially contribute to the rubber أکثرFor rolling pneumatic tires, the thermal induced effects are mainly resulted from visco-elastic behaviour of rubber parts and dissipation of stores strain energy during the cyclic deformations. It is noted that the operating conditions crucially contribute to the rubber hysteresis effect and temperature development in a rolling tire. In current study, an elaborated 3D FE model is worked up for simulating the certain inflation pressure, loading and velocity conditions for a specified radial tire. Special emphasis is given to transient temperature distribution of interior walls and tire cavities as critical zones. Compared with the experimental tests, the current study gives satisfactory results for time rate of change in temperature of tire walls and inside inflated air. تفاصيل المقالة -
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7 - Modelling of Non-Uniform Piezoelectric Micro-Cantilever in Different Environments
Mitra Taghizade A. H. Korayem M. H. KorayemIn recent years, Atomic Force Microscopy (AFM) has been known as a powerful and efficient tool for surface imaging in different environment. To enhance image quality and more precise prediction of Micro-cantilever (MC) behaviour, accuracy in the MC modeling and simulati أکثرIn recent years, Atomic Force Microscopy (AFM) has been known as a powerful and efficient tool for surface imaging in different environment. To enhance image quality and more precise prediction of Micro-cantilever (MC) behaviour, accuracy in the MC modeling and simulation and detecting the MC sensitivity to geometric parameters has great importance. To model the vibration motion of the AFM non-uniform piezoelectric MC, Timoshenko beam theory is used in order to consider the effect of shear effect in air and liquid environment. In addition, the effect of the forces imposed by the ambient and sample surface is considered. Frequency response has been studied in the air and different liquid environments and the obtained results have been compared with experiential results as well as with results obtained from Euler-Bernoulli beam theory that is reflective of higher precision exercised in the modeling in respect to Euler-Bernoulli beam theory. Efast statistical method, which is found efficient and quick in the survey of linear and nonlinear models and takes the inter-parameter coupling effect into consideration besides calculating the sensitivities unique to each of the factors, has been applied in order to analyse the geometrical parameters’ effects on the MC natural frequencies in the air and water environments. تفاصيل المقالة -
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8 - Stress and Displacement Analysis of First Molar Hollow Tooth during Dental Filling Operation using Three-Dimensional Finite Element Method
M. R. Karamooz-Ravari B. Shahriari E. Seyfalithe amount of rotten tooth that is come out of teeth is an important issue in dental filling because of its effects on strength of teeth. The main goal of this study is to determine a criterion for the amount of rotten tooth which can be brought out. To do so, first, a أکثرthe amount of rotten tooth that is come out of teeth is an important issue in dental filling because of its effects on strength of teeth. The main goal of this study is to determine a criterion for the amount of rotten tooth which can be brought out. To do so, first, a three-dimensional finite element model of the complex shape of Right First Molar Mandibular has been established. Then, cylindrical holes with different values of height and diameter (diameter of holes from 3 mm to 8 mm and height of 3 mm to 5.9 mm) is created on the cusp of the tooth. A uniform pressure (from 10 Pa to 10 kPa) is applied around the tooth resembling the belt which is utilized in reality. According to the obtained displacement and stress contours, the diameter of tooth hole can be increased up to 7 mm for pressures under 10 Pa while for higher pressures, the diameter of tooth hole can just be increased up to 6 mm. In addition, due to sudden increase in stress at a pressure of 10 kPa, increasing the value of pressure to higher values is not recommended. تفاصيل المقالة -
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9 - Optimization of the Forging Process of a Gas Turbine Blade using the Finite Element Analysis and Response Surface Method
V. Alimirzaloo F. R. BiglariForging of gas turbine blades needs a close control of the process parameters. These parameters require a suitable optimization method to achieve the best process conditions. This paper presents a hybrid method for the optimization of the forging process of an aerofoil أکثرForging of gas turbine blades needs a close control of the process parameters. These parameters require a suitable optimization method to achieve the best process conditions. This paper presents a hybrid method for the optimization of the forging process of an aerofoil blade. Forging process of the aerofoil blade was simulated using 3-dimentional finite element method. Preform shape and die parting-line angle are optimized in order to minimize the volume of the unfilled die cavity, material waste, and forging forces. The overall optimization scheme used in this research work includes a multi-objective approach that is a combination of response surface and finite element methods. The results show that the proposed optimization approach accrued to decrease the flash volume and the forging force of the aerofoil forging process. Therefore the proposed algorithm is a suitable method for the optimization of the gas turbine blade forging processes. تفاصيل المقالة -
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10 - Numerical Simulation of Fluid-Structure Interaction and its Application in Impact of Low-Velocity Projectiles with Water Surface
N. Khazraiyan N. Dashtian Gerami M. DamircheliIn this article, finite element method and ALE formulation were used to numerically simulate impact of low-velocity specific projectiles with water surface. For the simulation, Ls-Dyna finite element code was used. Material models which were used to express behavior of أکثرIn this article, finite element method and ALE formulation were used to numerically simulate impact of low-velocity specific projectiles with water surface. For the simulation, Ls-Dyna finite element code was used. Material models which were used to express behavior of air and water included Null material model. For the projectile, plastic-kinematics material model was applied. Mie-Gruneisen equation of state was also attributed to air and water. First, the results were validated by analyzing the impact of metallic cylinder with water surface and then impact of a mine as a low-velocity projectile was simulated. Among major outputs were force and pressure applied to the projectile, velocity and acceleration variations upon entering water, stress-strain variations and variations of water surface in various steps of analysis. The results showed that impact of structure with fluid can be modeled using finite element model with high accuracy in terms of quality and quantity. تفاصيل المقالة -
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11 - Experimental and Numerical Analysis of Titanium/HA FGM for Dental Implantation
Sina Sazesh Aazam Ghassemi Reza Ebrahimi Mohammad KhodaeiFGM dental implants are a very good alternative with respect to homogenous implants. In this study by focusing on mechanical property as one of the most important factors in implant design, the static behaviour of Ti/Nanostructure HA (hydroxyapatite) FGM dental implant أکثرFGM dental implants are a very good alternative with respect to homogenous implants. In this study by focusing on mechanical property as one of the most important factors in implant design, the static behaviour of Ti/Nanostructure HA (hydroxyapatite) FGM dental implant has been fabricated and investigated experimentally and numerically. At the first step, the nanostructure hydroxyapatite powders were synthesized by natural origin. At the second step, the initial powders were cold compacted in order to fabricate Ti/HA FGM samples for 4 different volume fraction exponents (N=1/3, 2/3, 1, 2). Then the compacted powders have been sintered using a vacuum furnace, in which compressive strength of each particular sample was finally assessed. A three-dimensional geometrical model of FGM dental implant system and surrounding bone was created by using the macro programming language in ANSYS software and then finite element analysis under static forces was performed. Finally the experimental results strength tests were compared with numerical solutions. According to the results, the FGM dental implants made of Ti/HA under static forces were sufficiently safe. As a result, FGM sample with volume fraction exponent of N=2/3 was chosen as the best sample. تفاصيل المقالة -
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12 - Behavior Analysis of Cold Expanded-Bolt Clamped AL2024-T3 Plate
M. Sayah Badkhor A. R. Naddaf Oskouei* H. Mohammadi Hooyeh F. ShirbakhtFor making rivet and bolt connections, making a hole is necessary. While basic S-N graph can be extracted from design documents, analysis of stress can be used for two different approaches. The first approach is the theoretical derivation of analytical relations with si أکثرFor making rivet and bolt connections, making a hole is necessary. While basic S-N graph can be extracted from design documents, analysis of stress can be used for two different approaches. The first approach is the theoretical derivation of analytical relations with simplified assumptions like planar stress or uniform bolt load distribution. The other one is the numerical simulation using robust codes like Abaqus software. By using these two approaches, residual stress distribution around the hole can be extracted in various conditions. In this experiment, an aluminium 2024-T3 plate with 3.2 mm thickness is considered. The stress analysis results and basic S-N graph were combined and discursive S-N graphs were obtained for different cold-expanded bolted holes. These graphs were compared with experimental data in several steps. First, the bolt fastening was considered. In the second step, cold expansion was considered and in the final step, the effects of fastening bolts and nuts and cold expansion was considered simultaneously. At last, a comparison between various steps was drawn. The results of this study showed that this new analytical method on distribution of residual stresses around cold expansion holes is as effectiveness as old methods. تفاصيل المقالة -
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13 - Process Parameters Optimization in Gas Blow Forming of Pin-type Metal Bipolar Plates using Taguchi and Finite Element Methods
M. Moradian A. Doniavi V. Modanloo V. AlimirzalooMetal bipolar plates are the most important parts of the fuel cells and recently these plates are used instead of graphite ones.In the present study, gas blow forming of a pin-type aluminum 5083 bipolar plate has been studied. After the simulation of the process, the FE أکثرMetal bipolar plates are the most important parts of the fuel cells and recently these plates are used instead of graphite ones.In the present study, gas blow forming of a pin-type aluminum 5083 bipolar plate has been studied. After the simulation of the process, the FE model has been validated using experimental results. Then, the effects of parameters including maximum pressure of the gas, pressurization profile and corner radius of the pin on thinning ratio and forming depth of final part have been investigated. Nine experiments were designed using the Taguchi L9 orthogonal array and the experiments were performed using the FE model. The signal to noise (S/N) ratio and the analysis of variance (ANOVA) techniques were carried out to determine the effective parameters and the contribution of each parameter. The maximum pressure of 1.2 MPa, SP2 pressurization profile and corner radius of 0.2 mm lead to the minimum thinning ratio. Also, it was found that to maximize the forming depth, the maximum pressure of 2 MPa, SP1 pressurization profile and corner radius of 0.3 mm should be selected. Also, ANOVA analysis showed that the most significant parameters on thinning ratio and forming depth are corner radius and maximum pressure, respectively. تفاصيل المقالة -
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14 - Multi layered finite element analysis of graded coatings in frictional rolling contact
R. Jahedi S. AdibnazariA plain strain analysis of frictional rolling contact on an elastic graded coating is presented in this paper. Finite element method is applied to gain an understanding of the stresses and contact zone properties caused during rolling contact. The effects of friction, m أکثرA plain strain analysis of frictional rolling contact on an elastic graded coating is presented in this paper. Finite element method is applied to gain an understanding of the stresses and contact zone properties caused during rolling contact. The effects of friction, material stiffness ratio and coating thickness on stresses in contact zone and coating/substrate interface are studied. Shear modulus of softening and stiffening graded coatings change with exponential, power law and linear functions. The substrate is homogenous and the rigid cylindrical roller moves in a steady state condition with constant velocity. The coating is modeled in multi layers and a 2-D hard contact of rolling surfaces is considered. The analytical results verify the present method and show a good agreement. It is shown that thinner thicknesses have more effects on stresses and energy density, but these effects are not seen for thicknesses larger than a specific limit. تفاصيل المقالة -
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15 - A study on the numerical simulation of thermo-mechanical behavior of the novel functionally graded thermal barrier coating under thermal shock
N. Nayebpashaee H. Vafaeenezhad S. M. M. Hadavi S. H. Seyedein M. R. Aboutalebi H. SarpoolakyAn attempt was made to investigate the thermal and residual stress distribution in a novel three layer (La2Zr2O7/8YSZ/NiCrAlY) during a real-like heating regime which includes heating, service time and final cooling. For achieving maximum accuracy and consistency in cal أکثرAn attempt was made to investigate the thermal and residual stress distribution in a novel three layer (La2Zr2O7/8YSZ/NiCrAlY) during a real-like heating regime which includes heating, service time and final cooling. For achieving maximum accuracy and consistency in calculation of thermal and mechanical properties of hybrid coating system, all related and required properties were introduced to the software in temperature-dependent mode. Element modification approaches like mass scaling leads to a considerable reduction in running time while satisfying and not violating accuracy and converging criteria and constrains. Applying adaptive hybrid meshing techniques which applies both mesh–part dependency and independency during numerical iterative solution avoids element distortion and diverging in coupled problem. Heat flux and nodal temperature contours indicated that, most of damaging and harmful thermal load and residual stresses concentrate on ceramic top coats and this may lead less harm and life time reduction in the substrate. تفاصيل المقالة -
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16 - Developing a control strategy for AFM nano- micro manipulation
H. RaeisiFard A. K. HoshiarNowadays, with the growing use of AFM (Atomic Force Microscope) nanorobots in the fabrication of nanostructures, research in this area has been proliferated. The major limiting of manipulation process is the lack of real-time observation. Computer simulations have been أکثرNowadays, with the growing use of AFM (Atomic Force Microscope) nanorobots in the fabrication of nanostructures, research in this area has been proliferated. The major limiting of manipulation process is the lack of real-time observation. Computer simulations have been widely applied to improve the feasibility of the process. The existing 2D strategies are incapable of presenting the feasibility of the process. Therefore, 3D simulations of effective forces during the manipulation process and the control mechanism of the process have been presented in this research, where the effective parameters are investigated. To evaluate the validity of the presented results, a FEM simulation is proposed. It is observed that the two sets of results (the analytical method and the finite element approach) have adequate correlation, while the discrepancy which is in an acceptable range, is due to the different solving technique of the finite element method. By applying the presented models, it is now possible to accurately predict the effective forces for fabricating the nanostructures. تفاصيل المقالة -
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17 - Characterization of Stress Concentration in Thin Cylindrical Shells with Rectangular Cutout Under Axial Pressure
O. Sam Daliri M. FarahaniIn this paper, stress concentration in the thin cylindrical shell with rectangular cutout subjected to uniform axial pressure was investigated using a parametric finite element model. Design of experiments techniques and statistical analysis was used to provide a model أکثرIn this paper, stress concentration in the thin cylindrical shell with rectangular cutout subjected to uniform axial pressure was investigated using a parametric finite element model. Design of experiments techniques and statistical analysis was used to provide a model for characterizing the critical stress in these components. The influences of the geometrical parameters and their combinations were studied in detail. It was observed that the length to width ratio of the cutout, the length and the radius to thickness ratio of the cylinder were significant parameters for describing the stress concentration around the cutout, respectively. By increasing the length to width ratio as a main effective geometrical factor in the stress concentration, the stress around the cutout was increased significantly. Based on the statistical analysis conducted in this study, a formula was derived which can predict the stress concentration around the cutout of the cylinder with the accuracy more than 84% (R2 = 88.7%, R2pred = 84.6%, R2adj= 86.7%). تفاصيل المقالة -
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18 - Investigation on Stress Distribution of Functionally Graded Nanocomposite Cylinders Reinforced by Carbon Nanotubes in Thermal Environment
Mohammad morad Sheikhi Hamidreza Shamsolhoseinian Rasool Moradi dastjerdiIn this paper, stress and displacement fields of functionally graded (FG) nanocomposite cylinders reinforced by carbon nanotubes (CNTs) subjected to internal pressure and in thermal environment are investigated by finite element method. The nanocomposite cylinders are c أکثرIn this paper, stress and displacement fields of functionally graded (FG) nanocomposite cylinders reinforced by carbon nanotubes (CNTs) subjected to internal pressure and in thermal environment are investigated by finite element method. The nanocomposite cylinders are combinations of single-walled carbon nanotubes (SWCNTs) and isotropic matrix. Material properties are estimated by a micro mechanical model (Rule of mixture), using some effective parameters. In this simulation, an axisymmetric model is used; uniform and four kinds of linear functionally graded (FG) distributions of CNTs along the radial direction is assumed, in order to study the stress distributions. Effects of the kind of distribution and volume fraction of CNT and also, thermal environment, and geometry dimension of cylinder are investigated on the stress and displacement distributions of the FG nanocomposite cylinders. It is shown that, CNTs distribution and environment temperature are important factors on the stresses distribution of the nanocomposite cylinders. تفاصيل المقالة -
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19 - Numerical Analysis of Circular Pre-notched U-Channel Section Distortions in Cold Roll-Forming Process
S. Sattar S. Mazdak E. SharifiCold roll forming is a process in which a metal sheet gets a desired section form by passing through a series of rotating rollers. Predicting the amount of the distortion in pre-notched cold formed sections still remains challenging in cold roll forming industry, depend أکثرCold roll forming is a process in which a metal sheet gets a desired section form by passing through a series of rotating rollers. Predicting the amount of the distortion in pre-notched cold formed sections still remains challenging in cold roll forming industry, depending on the shape and position of the holes. This study investigates the influence of variation of the design parameters on the defects of the U-channel sections produced by cold roll forming process with circular pre-notches. To analyze the important parameters in deforming the circular holes during the cold roll forming of U-channel sections, a three-dimensional finite element model has been taken into account. A range of variation for design factors in forming the U-channel sections with pre-notches is set, including radius of circular holes, distance between the holes and the flange edge, hole spacing, sheet thickness, and type of material. Furthermore, using the response surface methodology, a set of tests are designed and modeled employing Finite Element analysis. Afterward, a set of output parameters such as edge buckling, the wave of the holes, the change in hole size, hole spacing, and the distance between the holes and the edge of the flange, are considered. Utilizing Analyses Of Variance (ANOVA), the accuracy of the linear regression models was conducted in this study. The accuracy of the simulated models is examined by comparing the analysis results with the experimental results. Finally, the effect of the important parameters on the defects of the product has been extracted in both the statistical form as well as mathematical functions applying response surface methodology. The results show that as the radius of the hole increases, edge buckling increases. The increase of the hole radius increases the edge wave on the holes. The hole width of the product is bigger and the hole length is smaller than the nominal measuring. تفاصيل المقالة -
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20 - Experimental and Numerical Investigation of the Arms Displacement in a New Electrothermal MEMS Actuator
M. Kolahdoozan A. Rouhani Esfahani M. HassaniMicrogrippers can be effectively applied for handling, positioning and assembling of the micro components. In the present study, a new design of a U-shape electrothermal microgripper was fabricated and developed with the voltages correspond between 1 to 10 volts. The mi أکثرMicrogrippers can be effectively applied for handling, positioning and assembling of the micro components. In the present study, a new design of a U-shape electrothermal microgripper was fabricated and developed with the voltages correspond between 1 to 10 volts. The microgripper was made of silicone with thickness of 25 microns, and pieces between 460 to 480 microns. The proposed microgripper has a simpler design and more facile fabrication comparing to most reported electrothermal microgripper. The behavior of the microgripper was simulated in COMSOL software to measure the displacement of the arms which hold and heat generations during the voltage changes. The present microgripper has more thermal and voltage tolerance comparing to other electrothermal microgripper. Furthermore, the obtained amount of tip displacement for voltage changes is acceptable. Another simulation method based on a three layer artificial neural network model (ANN) was carried out. Feed forward back propagation algorithm was employed as training algorithm to predict the displacement. The obtained results from both models proved that ANN model had better estimation due to the mean absolute percentage error of 1.024% and determination coefficient of 0.9995. Moreover, they confirm higher capability and accuracy of ANN in prediction of arms displacement compared to FEM. تفاصيل المقالة -
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21 - Experimental Study and Finite Element Simulation of Residual Stress in Welded Sections of Steel P91 Pipes with Multi-pass Welding
Davood Azadi Nosratollah Solhjoei SayedAli MousaviAll the producing and assembling processes exert residual stress on the pieces that may lead to structural failure. Therefore, calculating the residual stress in such structures has been common in recent years. In this article, distribution of temperature and residual s أکثرAll the producing and assembling processes exert residual stress on the pieces that may lead to structural failure. Therefore, calculating the residual stress in such structures has been common in recent years. In this article, distribution of temperature and residual stress resulting from arc welding in three-pass butt joint in P91 austenitic stainless steel pipes is calculated and estimated using the finite element method and experimental data. Simulating the welding process has been carried out three- dimensionally using Abaqus software. Distribution of the arc thermal flux has been identified based on the Goldak two-elliptical model using DFLUX subprogram in Abaqus software. The numerical method has been employed by doing thermoelastoplastic analysis and the technique of birth and death of the elements to model the welding passes and the melted elements. Then, using central hole drilling method, residual stress gradient of the thickness at distance 3mm from the welding line on the pipe is measured. Finally, the maximum percentage of error, through the results obtained from experimental measurements and finite element method, was reported 27% which is scientifically reasonable. The results show that the residual environmental stress in the internal surface of the pipe from the welding central line to 8.7mm varies with the gradient of 610MPa from 296MPa to -314MPa. Such a drastic stress distribution leads to genesising some cracks on the welded pipes. تفاصيل المقالة -
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22 - Application of Topology Optimization in Design of Stem Profile in Hip Implants Using Finite Element Method
Mohammad Reza Niroomand Farzad BoroomandAppropriate design of stem shape is an important factor in total hip replacement. It affects the attachment of the implant to the bone and the stability of the implant. Using topology optimization, this study has been an attempt to propose an optimized model of the stem أکثرAppropriate design of stem shape is an important factor in total hip replacement. It affects the attachment of the implant to the bone and the stability of the implant. Using topology optimization, this study has been an attempt to propose an optimized model of the stem profile of the hip implants. In this regard, a three-dimensional finite element model of the implant has been combined with a stiffness-based topology optimization algorithm to reduce the relative motion between the implant and the bone. The objective function in the optimization problem is the compliance of the structure which should be minimized. Also, a constraint on usable volume is applied to the structure. Then smoothing process has been done on the optimal model to prevent its geometric complexities. Results show that the final model has a smaller weight, less displacement, and more uniform stress distribution. In addition, using conventional production methods, this model can be easily produced. تفاصيل المقالة -
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23 - Steady State Creep Characteristics of a Ferritic Steel at Elevated Temperature: An Experimental and Numerical Study
Roozbeh Alipour Ali Farokhi Nejad Hamid Nilsaz DezfouliPrediction of creep life for a ferritic steel plate is significant in the context of its application as an element of steam generating systems. In this paper, the issue of elevated temperature creep in 2.25Cr–1Mo steel was investigated in detail, including the mec أکثرPrediction of creep life for a ferritic steel plate is significant in the context of its application as an element of steam generating systems. In this paper, the issue of elevated temperature creep in 2.25Cr–1Mo steel was investigated in detail, including the mechanism and the compatibility of hyperbolic sine modeling methodology for the description of steady state creep behavior of this alloy. Creep rupture tests were conducted on the thin foil samples at an elevated temperature ranging from 973 to 1073 K at various stresses between 90 to 210 MPa. A hyperbolic sine model is then used to fit the experimental creep data and the corresponding best fit parameters are provided. Using these parameters, a finite element analysis employing ABAQUS was carried and the reliability of the hyperbolic sine model was investigated in relation to the creep curve and creep life in the steady state creep area. The main outcome of the current study is creep characterisation of 2.25Cr–1Mo steel foils at extreme elevated temperature and to propose a finite element model for simulating this condition which is not reported so far. The results of experimental, constitutive analysis and finite element simulation were compared to each other and it was shown that they are in a good agreement. تفاصيل المقالة -
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24 - Multi-Objective Optimization of Loading Paths for Double-Layered Tube Hydroforming using Finite Element Analysis
Hamed Ebrahimi Keshmarzi Ramin Hashemi Reza MadoliatOne of the most important studies in tube hydroforming process is optimization of loading paths. The primary purpose of this research is to maximize formability by detecting the optimal forming parameters. The most significant settings in the prosperity of tube hydrofor أکثرOne of the most important studies in tube hydroforming process is optimization of loading paths. The primary purpose of this research is to maximize formability by detecting the optimal forming parameters. The most significant settings in the prosperity of tube hydroforming process, are internal pressure and end axial feed (i.e., load path). In this paper, a finite element analysis was performed for a double-layered tube hydroforming process using the ABAQUS/Explicit software. Then, the finite element model has been verified with published experimental data. Using design of experiments (DOE) working with the Taguchi method, 32 loading paths are designed for optimization. All 32 loading paths are modelled using the finite element method in ABAQUS/Explicit and the magnitudes of bulge height and the total thickness of tubes at the branch tip are obtained in each loading path. The regression analysis is carried out to estimate the tubes formability and obtain objective functions that are bulge height and the total thickness of tubes at the protrusion peak as functions of loading parameters (internal pressure and axial feed). For solving the multi-objective optimization problem, the non-dominated sorting genetic algorithm II (NSGA-II) is utilized and the optimum results were obtained from the Pareto optimal front. Finally, the optimized loading path was applied to the finite element model and better formability (3.4% increase in the bulge height) has been achieved in the results. تفاصيل المقالة -
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25 - Numerical simulation of multilayer cellular scaffolds with 3D and 1D elements
Hamid Reza khanaki Sadegh Rahmati Mohammad Nikkhoo Mohammad Haghpanahi Javad AkbariIn this paper, an attempt has been made to provide a numerical method for investigating the mechanical properties of multilayer scaffolding. These scaffolds can be used as implants in bone fractures. For this purpose two numerical simulation methods are introduced to pr أکثرIn this paper, an attempt has been made to provide a numerical method for investigating the mechanical properties of multilayer scaffolding. These scaffolds can be used as implants in bone fractures. For this purpose two numerical simulation methods are introduced to predict the elastic properties of multilayer cell scaffolds. These simulations are based on two models: a 3D model with a volumetric element, and a 1D model with a linear element. To compare the results of these models, three types of two- and three-layer titanium alloy scaffolds have been simulated by the two methods. Also, Young's modulus of the scaffolds has been compared with the experimental conclusions of earlier studies. The results confirm that simulations with 1D models are more cost-effective compared to 3D ones. Additionally, because of the more reliable agreement of Young's modulus results of numerical modeling with the linear element (1.8 to 5 times) compared to the volumetric element (11 to 23 times) compared to the experimental findings, the numerical method with the linear elements can be a reliable tool for studying multilayer scaffoldings. تفاصيل المقالة -
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26 - Numerical Simulation of Ultrasonic Assisted Indentation Tube Forming
Saeid Dashti Masih Paknejad Amir Abdullah Abbas PakIndentation forming is an internal tube forming process in which a mandrel with a diameter slightly larger than that of the tube is pressed inside the tube and in so doing, creates the internal profile. Forming forces have a significant effect on the spring back, residu أکثرIndentation forming is an internal tube forming process in which a mandrel with a diameter slightly larger than that of the tube is pressed inside the tube and in so doing, creates the internal profile. Forming forces have a significant effect on the spring back, residual stress, quality of the inner surface, quality of tube dimensions, and tool wear. In this study, the forming process of CK45 steel tube by carbide tungsten tool in the presence of ultrasonic vibration has been simulated and the effect of ultrasonic on the forming mechanism has been investigated by introducing two regimes according to the forming conditions. The effects of tool feed-speed and amplitude of vibration on forming force reduction have been investigated. According to the simulation results, the main reason for the force reduction in the presence of longitudinal tube ultrasonic vibration is the intermittent phenomenon which is the continuous or impulsive regime. The critical amplitude which determines the borderline of continuous and impulsive regimes is obtained 38µm by the simulation of the process. The maximum force reduction obtained in continuous regime is 64.2% at the critical amplitude. The simulation results are consistent well with the previous experimental data. تفاصيل المقالة -
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27 - The Numerical Modeling to Study the Multi-Pass Friction Stir Processing on Magnesium Casting Alloy AZ91
hoda agha amini fashami Mohammad Hoseinpour Gollo Nasrollah Bani Mostafa Arab Bahram NamiIn this research, the multi-pass friction stir processing on AZ91 alloy has been simulated with the three-dimensional numerical modeling based on the ABAQUS/ Explicit. This simulation involves the Johnson-Cook models for defining the material behavior during this intens أکثرIn this research, the multi-pass friction stir processing on AZ91 alloy has been simulated with the three-dimensional numerical modeling based on the ABAQUS/ Explicit. This simulation involves the Johnson-Cook models for defining the material behavior during this intense plastic deformation and investing the fracture criterion. Friction stir processing is a complex process that includes several issues such as high strain rate deformation, microstructure evolution, the asymmetric flow of material, and heat. Therefore, the modeling of this process is challenging. This model simulates the tool plunging and stirring phases in the two-pass process. In this paper, to prevent too much damage in the elements during processing, the Arbitrary Lagrangian-Eulerian technique for automatically remeshing of distorted elements has been used. This work shows that the numerical modeling can be an efficient method to study the effect of process parameters on the thermal evolution and the stress distribution. The thermal model was calibrated using the experimental results from the previous works. This model can predict the transient temperature distribution and residual stress field during FSP on AZ91. The results show that the maximum temperature in the advancing side is more than that in the retreating side. In addition, numerical results show that at the end-position of the process, the tool during the lift-up leaves the keyhole region in a compressive stress state. تفاصيل المقالة -
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28 - Micro-Finite Element Model to Investigate the Mechanical Stimuli in Scaffolds Fabricated via Space Holder Technique for Cancellous Bone
Sayed Alireza Hashemi Saeid Esmaeili Mazyar Ghadirinejad Saeed Saber-Samandari Erfan Sheikhbahaei Alireza Kordjamshidi Amirsalar KhandanIn Osteoporosis, bone mechanical strength decreases and as a result, the risk of bone fracture increases. Osteoporosis is also referred as a "silent illness" since it usually develops asymptomatic until it breaks a long bone, like the femur. In recent years, porous scaf أکثرIn Osteoporosis, bone mechanical strength decreases and as a result, the risk of bone fracture increases. Osteoporosis is also referred as a "silent illness" since it usually develops asymptomatic until it breaks a long bone, like the femur. In recent years, porous scaffolds have been utilized to repair damaged bone tissue. For bone tissue engineering, synthetic scaffolds should have acceptable mechanical properties, in addition to the required biological properties. In this regard, the finite element simulation is used to predict the mechanical properties of porous bone scaffolds as one of the most common methods for reducing the experimental tests, because the acquisition of mechanical properties of such scaffolds is very time-consuming and expensive. Due to the widespread use of hydroxyapatite (HA) in the manufacture of bone scaffold composites, the mechanical properties of HA-wollastonite scaffold composites are obtained by laboratory tests and finite element methods. Comparison of the simulation of finite element analysis (FEA) and the experimental results indicate the success of the FEA simulation. In conclusion, new finding satisfied expectations as being suitable for mechanical and biomaterial aspect of a porous scaffold which is proven by laboratory tests and FEA simulations. Due to that fact, the result of this study can be employed to obtain scaffolds well-suited for bone implementations. تفاصيل المقالة -
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29 - Influences of Blank Holder Force in The Multi-Step Deep Drawing Process of Aluminum Sheets
Sajad Bakhtiari Seyed Jalal Hashemi Amir Hossein RoohiIn recent decades, the use of aluminium alloys is developed in the automotive industry with regard to the need for lightweight and anti-corrosion components, one of which is AA7075 Al alloy. In this study, the multi-step deep drawing process of AA7075 aluminium sheets u أکثرIn recent decades, the use of aluminium alloys is developed in the automotive industry with regard to the need for lightweight and anti-corrosion components, one of which is AA7075 Al alloy. In this study, the multi-step deep drawing process of AA7075 aluminium sheets under various blank holder forces is investigated through a numerical simulation and is then validated with experimental results. Simulations were conducted by ABAQUS finite element software, and the influences of the blank holder force on the wrinkling height, rupture occurrence and thickness distribution of the sheet were studied. The optimum amount of blank holder force at each drawing step is determined so that the height of wrinkling, and the thinning percentage do not exceed the permissible value. Based on the results, the blank holder force magnitude should be considered descending during the four successive steps to achieve more uniform thickness distribution, and also the wrinkling height could be reduced by increasing the blank holder force in the analysed force range. The optimum amount of blank holder force in the four drawing steps was 28000, 2500, 1500 and 600 N, respectively. In general, the minimum thickness was created in the corner of the punch. The results also showed that an excessive increase in the blank holder force in order to eliminate the wrinkling caused the thinning percentage to increase. Finally, a good accordance between the experimental and numerical results was observed. تفاصيل المقالة -
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30 - Investigation on Failure Loads and Failure Modes for Two Parallel Pin-Loaded Holes Made from Unidirectional Glass-Epoxy Nanoclay Laminates
sajjad dehghanpour keivan hosseini safari Farzan Barati Mohammadmahdi AttarPurpose of this study is to obtain failure modes and failure loads of two Parallel pin loaded holes in unidirectional glass fibre/epoxy by adding nanoclay in the absence of nanoclay composite laminates using finite element analysis; the results are validated through exp أکثرPurpose of this study is to obtain failure modes and failure loads of two Parallel pin loaded holes in unidirectional glass fibre/epoxy by adding nanoclay in the absence of nanoclay composite laminates using finite element analysis; the results are validated through experiment. The geometrical parameters studies in this survey include the distance between the diameter of the hole (e/d) and the free edge of specimen, the distance between two holes-to-hole diameter (M/d). The samples were exposed to constant speed tensile loading. The results showed that by adding nanoclay, failure load increases and failure modes varies from shear out to bearing failure. Furthermore, increasing distance from the free edge of the pin centre’s increases load bearing capacity of two type of composite materials and changes the failure mode from shear to the bear, it increases and decreases the distance from canter’s of pin in layers with and without nanoclay particles, respectively and changes failure mode from shear to bear mode. In order to find morphology of specimens and dispersion quality, Scanning Electron Microscope (SEM) was used. For predicting failure load and differentiating failure modes, Tsai-hill failure criteria associated with material property degradation is used. Experimental and FEM results indicate importance of considering the impact of e/d and M/d ratios in the design of two Parallel pin joints. ANSYS was used to carry out numerical simulation and the results denote a good agreement between numerical and experimental results. In this study, by designing an experimental and numerical procedure to estimate the effect of nanoclay, on failure mode and failure load of typical composite material, glass-epoxy, we could illustrate that adding nanoclay brought with it improvement of shear and tensional strength of glass-epoxy about 10 %. تفاصيل المقالة -
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31 - Dynamic Analysis of Carbon Nanotube-Reinforced Multilayer Composite Plates
Jamshid Ebrahimi Jafar Eskandari Jam Reza Azarafza Mohsen Heydari Beni Majid Eskandari ShahrakiThe paper studied the analysis of vibrations of rectangular carbon nanotube-reinforced composite plates. To this end, a three-layer nanocomposite plate - two layers with the targeted distribution of carbon nanotubes as FG-X at the top and bottom and a layer without an a أکثرThe paper studied the analysis of vibrations of rectangular carbon nanotube-reinforced composite plates. To this end, a three-layer nanocomposite plate - two layers with the targeted distribution of carbon nanotubes as FG-X at the top and bottom and a layer without an amplifier in the middle of the plate - were analyzed. The governing equations for this problem are based on First-order Shear Deformation Theory (FSDT). The distribution of nanotubes on these plates is as targeted FG-X. The effect of various types of SWCNTs distributions in the direction of thickness on the vibrational behavior of nanocomposite plates was examined. The effective properties of nanocomposite materials Functionally Graded Carbon Nanotube-Reinforced Composite (FG-CNTRC) were estimated using the rule of mixtures. Detailed parametric studies were performed to determine the effects of the volume fraction of carbon nanotubes and the thickness-to-length ratio of the plate on the natural frequency responses and the shape of the plate mode. The equations obtained in this problem were coded in MATLAB software, the nanocomposite plate was modelled in ABAQUS software, and the comparison of the results obtained from the numerical solution with ABAQUS software showed relatively right consistency with the results obtained from the analytical solution. تفاصيل المقالة -
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32 - Analytical and Numerical Study of Pre-Stress Effect in Piezoelectric Sandwich Type Ultrasonic Transducer
Hamidreza Nadri Mahdi Shaban Abbas PakIn this paper, the effect of pre-stress condition on the resonance frequency of the transducer is studied by using numerical and analytical methods. To compare the obtained results, two sandwich-type transducers with nominal frequency of 25 kHz and 30 kHz are considered أکثرIn this paper, the effect of pre-stress condition on the resonance frequency of the transducer is studied by using numerical and analytical methods. To compare the obtained results, two sandwich-type transducers with nominal frequency of 25 kHz and 30 kHz are considered. Experimental determination of pre-stress value in transducer is described and measured. Then resonance frequency of transducers in the presence of pre-stress is determined by impedance analyser. Numerical analysis is conducted by modelling three-dimensional transducer in details at ABAQUS software. The resonance frequency is determined with and without pre-stress. The FE results show that by applying pre-stress on the transducers, the resonance frequency of transducers decreased. Furthermore, the FE results are very close to experimental results. Furthermore, a systematic analytical solution is presented based on one-dimensional wave propagation. The resultant displacement for each sub-section of the transducer is calculated and then all of them are assembled and solved by considering the continuity conditions of displacement and force components. It is found that pre-load condition that is produced by central bolt reduces resonance frequency of the transducer. The obtained analytical results provide fast and reliable model for predicting resonance frequency of transducer. تفاصيل المقالة -
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33 - Weld Distortion and Residual Stresses in Aluminum Hollow Section T-Joint
Asghar Mahdian Arash Babamiri Behrooz ShahriariWelding is known as one of the most popular attaching methods for different hollow section components. However, local concentrated heating, distortion, and residual stresses at welded joints are unavoidable. In this article, the welding simulation for rectangular hollow أکثرWelding is known as one of the most popular attaching methods for different hollow section components. However, local concentrated heating, distortion, and residual stresses at welded joints are unavoidable. In this article, the welding simulation for rectangular hollow (RHS) sections for the front axle carrier of the new BMW series-7 is discussed and weld distortion and residual stresses in its aluminum T-joint for one proposed sequence are investigated. Comparisons of the results of this paper for this recommended sequence with experimental results in some references show good agreement and indicate that characteristics of the welding distortions are fully forecasted. In the following of this paper, the Finite Element Method (FEM) is used to offer a better sequence with smaller weld distortion and residual stresses. Weld distortion and residual stresses are highly influenced by welding strategy. In the proposed strategy, the needed time to perform the welding process decreased, and the total weld distortion and residual stresses decreased by 24% and 4%, respectively. تفاصيل المقالة -
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34 - Numerical and Experimental Static Bending Analysis of Composite Sandwich Panels with Grid-Stiffened Cores Before and After Transverse Impact Loading
Ali Asghar Davoodabadi Ali Davar Mohsen Heydari Beni Jafar Eskandari JamNowadays grid structures are considered as one of the most useful composites because of their various applications. Since grid structures are vulnerable to impact loads, they should be investigated under such loadings. The present paper studies the low-velocity impact l أکثرNowadays grid structures are considered as one of the most useful composites because of their various applications. Since grid structures are vulnerable to impact loads, they should be investigated under such loadings. The present paper studies the low-velocity impact loading of sandwich panels with grid-stiffened cores using both experimental and numerical simulations. In addition to the impact behaviour and the resultant damage of the sandwich panels, the behaviour of these structures under three-point bending was studied before and after the impact loading. The results were provided for impact and bending loadings separately. Then the effect of impact loadings on bending strength was investigated and it was found that the impact loading decreases the bending strength. A consistency between numerical and experimental results was also observed, which confirms the applicability of the Finite Element Method (FEM) in simulating the behaviour of such structures under impact and bending loads, while saving lots of time, efforts and costs. تفاصيل المقالة -
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35 - Investigation of In-Situ Compressive Strength of Fiber-Reinforced Mortar and the Effect of Fibers on the Adhesion of Mortar/Steel
Ali Saberi Varzaneh Mahmood NaderiThe proper connection between mortar and steel is one of the crucial issues in civil engineering. This paper has investigated the effect of polypropylene fibbers on the bond between cement mortar and steel, using “Twist-off” and “pull-off” tests. أکثرThe proper connection between mortar and steel is one of the crucial issues in civil engineering. This paper has investigated the effect of polypropylene fibbers on the bond between cement mortar and steel, using “Twist-off” and “pull-off” tests. Moreover, in order to assess the in-situ mechanical properties of fibre-reinforced mortars, the correlation of records obtained from semi-destructive methods of “Twist-off” and “pull-off” with those of laboratory tests was determined, and calibration curves were provided, using the regression analyses. The mentioned tests were modelled with the ABAQUS software to evaluate the distribution of stresses and cracks developed during the semi-destructive tests. The results show that the addition of polypropylene fibbers reduces the shrinkage of mortars by about 13% and this has a direct effect on the bond between the mortar and steel. So that the shear and tensile bond of fibre-reinforced mortars at 90 days is 75% and 94% higher than conventional mortars, respectively. The reason for this is the effect of fibbers on the process of hydration of mortars and also to prevent excessive opening of cracks, which is shown by SEM. According to the results, instead of using an expensive and imported pull-off device, a cheap and internal twist-off device can be used to measure adhesion. Also, to evaluate the compressive strength of mortars, twist-off and pull-off tests can be used by placing the readings obtained in the equations y = 0.156x + 0.329 and y = 0.055x-0.001 instead of x, respectively, to evaluate the compressive strength of mortars. تفاصيل المقالة -
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36 - Simulation and Dynamic-Thermal Analysis of Ceramic Disc and Brake Pad for Optimization by Finite Element Method
Navvab Gholami Ahmad Afsari Seyed Mohammad Reza Nazemosadat Mohammad Javad AfsariThe braking system in cars is directly deals with the issue of safety, and as a result, it is essential to pay attention to this matter. One of the materials used to make disc and brake pads in disc brakes is a ceramic material. This research aims to simulate and analyz أکثرThe braking system in cars is directly deals with the issue of safety, and as a result, it is essential to pay attention to this matter. One of the materials used to make disc and brake pads in disc brakes is a ceramic material. This research aims to simulate and analyze the dynamic-thermal ceramic brake disc during the braking operation using the finite element method. Currently, the conventional brake disc is used in the Peugeot 206 car (domestic production), which has low efficiency in terms of life, wear, etc. Therefore, in this research, considering the significant production of Peugeot 206 car in the country, the disc and brake pads of this car have been selected, which were first modeled by Catia software, and after transferring the model to Abacus software and defining the types of ceramics and Cast iron was analyzed by finite element method. Compared the results of the Peugeot 206 ceramic brake disc and pad analysis were with the results of the standard (cast iron) discs in this car. The results showed that the maximum von Mises stress in the ceramic disc was 260.7 MPa, while the maximum von Mises stress in the cast iron disc was 293.3 MPa. The amount of heat produced in the ceramic disc during the braking action in 4 seconds was almost 84% less than the cast iron disc in the same period. Also, the results showed that the ceramic disc has a higher safety factor (1.98) than the cast iron disc (1.45). تفاصيل المقالة -
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37 - Different Geometry Design Structures of Tissue Scaffolds for Additive Manufacturing
amirhossein Ehsani sadegh rahmati Mohammad Nikkhoo Shahram Etemadi Haghighi Mohammad HaghpanahiThe design and manufacturing cubic porous scaffolds are a considerable notion in tissue engineering (TE). From Additive manufacturing (AM) perspective, it has attained high appeal in the string of TE during the past decade. In the view of TE, the feasibility of manufact أکثرThe design and manufacturing cubic porous scaffolds are a considerable notion in tissue engineering (TE). From Additive manufacturing (AM) perspective, it has attained high appeal in the string of TE during the past decade. In the view of TE, the feasibility of manufacturing intricate porous scaffolds with high accuracy contrast to prominent producing methods has caused AM the outstanding option for manufacturing scaffold. From design perspective, porous scaffold structures play a crucial task in TE as scaffold design with an adequate geometries provide a route to required strength and porosity. The target of this paper is achieve of best geometry to become an optimum mechanical strength and porosity of TE scaffolds. Hence, the cubic geometry has been chosen for scaffold and Cube, Cylinder and Hexagonal prism geometries have been selected for pore of structures. In addition, for noticing the porosity effects, pore size has been chosen in three size, and a whole of nine scaffolds have been designed. Designed scaffolds were generated using Fused Deposition Modeling (FDM) 3D Printer and dimensional specifications of scaffolds were evaluated by comparing the designed scaffolds with Scanning Electron Microscope (SEM). The samples were subjected to mechanical compression test and the results were verified with the Finite Element Analysis (FEA). The results showed that firstly, as the porosity increases, the compressive strength and modulus of elasticity obviously decreased in all geometry pore scaffolds. Secondly, as the geometry changes in similar porosity, cubic pore scaffold achieved higher compressive strength and modulus of elasticity than cylinder and hexagonal prime. Experimental and FEM validated results proposed a privileged feasible pore geometry of cubic scaffold to be used in design and manufacturing of TE scaffolds. تفاصيل المقالة -
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38 - Numerical Simulation of Hot Forging Process of KIA Car Brake’s Output Shaft
saeid Hashemian Peyman Mashhadi Keshtiban Abuzar Es'haghi OskuiThe present study investigates the production process by closed die forging method of one of the sensitive and safe parts of KIA car brake, which is affected by various mechanical and thermal stresses in its operating conditions; therefore, in the present research, the أکثرThe present study investigates the production process by closed die forging method of one of the sensitive and safe parts of KIA car brake, which is affected by various mechanical and thermal stresses in its operating conditions; therefore, in the present research, the application of this forming method in the Iranian automotive industry has been discussed. In this study, an attempt was made using finite element analysis in ABAQUS software to determine the maximum force required for forging this part. In addition, the influence of various parameters such as the temperature of the part during the forming process, the coefficient of friction between the part and the die, as well as the strain rate have been investigated. The results indicated that the friction coefficient has a significant effect on the maximum required force, and the maximum values of the load increase with increasing the friction coefficient; but the remarkable result is that the effect of this coefficient is negligible from a value onwards. This point is consistent with the observations in practice. Besides, a strong dependence of the results on the loading speed was observed, and the required force has increased with increasing loading speed for reasons such as the strain hardening phenomenon. Also, the force required for forging has decreased with increasing the temperature, which is due to reduced material strength. This reduction from 900°C to 1000°C is less than 2%, while it is approximately 40% from 1000°C to 1100°C, which is consistent with the experimental reports. تفاصيل المقالة -
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39 - Evaluation of Critical Buckling Load in FG Plate using Analytical and Finite Elements Methods
Hossein Ahmadi Rashid AMIR GHIASVAND Maziar Mahdipour Jalilian Mahdi KazemiIn this paper, analytical and finite element solutions of mechanical buckling of a thick Functionally Graded (FG) plate have been investigated. Boundary conditions have been assumed as simply supported at all edges and three different loadings have been applied. In anal أکثرIn this paper, analytical and finite element solutions of mechanical buckling of a thick Functionally Graded (FG) plate have been investigated. Boundary conditions have been assumed as simply supported at all edges and three different loadings have been applied. In analytical section the procedure of developing the critical buckling force by third order shear theory has been presented and then the stability Equations have been reduced from 5 to 2. In continue, the problem has been solved using numerical simulation by ABAQUS. To validate the FEM, results have been compared and validated with analytical solution. The results show that the bi-axial compression loading case with the loading ratio of R to one and R to zero are the most possible and most unlikely case in buckling occurrence, respectively. تفاصيل المقالة -
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40 - Numerical and Experimental Investigation of Natural Frequency and Damping Coefficient of Flexible Cellular Lattice Structures
Amir Hosein Samimi M. R. Karamooz-Ravari Reza DehghaniCellular lattice structures encompass a class of metamaterials characterized by the arrangement of interconnected struts and/or plates, offering an adaptable microstructure that enables a broad range of property control. These structures have garnered significant attent أکثرCellular lattice structures encompass a class of metamaterials characterized by the arrangement of interconnected struts and/or plates, offering an adaptable microstructure that enables a broad range of property control. These structures have garnered significant attention for their distinctive properties and have found widespread application across industries such as aerospace, medical, pharmaceutical, automotive, defense and safety. This study seeks to explore the impact of geometric parameters on the natural frequency and damping coefficient of cellular lattice structures. Samples featuring BCC and OCTET architectures with varying porosities were initially produced using fused deposition modeling (FDM). Subsequently, both experimental and numerical analyses were conducted to assess the first natural frequency and damping coefficient of these materials. Comparison of the numerically obtained results with experimental data revealed a strong agreement. The findings indicate that, for both BCC and OCTET lattices, an increase in porosity is associated with a decrease in both natural frequency and damping coefficient. تفاصيل المقالة -
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41 - Finite Element Analysis of the Impact Behavior of Sandwich Panels with Nanocomposite Face sheet (Epoxy/ Fiberglass/Nanosilica)
Arash Azadi Mahdi Karami Khorramabadi Maziar Mahdipour JalilianIn this research, the impact behavior of nanocomposite sandwich panels with epoxy/fiberglass/nanosilica face sheet were assessed by the finite element method. In the first step, the mechanical properties of the nanoparticle-containing composite should be obtained. A uni أکثرIn this research, the impact behavior of nanocomposite sandwich panels with epoxy/fiberglass/nanosilica face sheet were assessed by the finite element method. In the first step, the mechanical properties of the nanoparticle-containing composite should be obtained. A unit cell of fabric was designed in Catia software and placed within the designed polymeric matrix. The mechanical properties of this unit cell were defined as a new matrix and the nanoparticles were randomly dispersed in the new matrix using a Python code. The elastic properties of the modeled nanocomposite were obtained using Abaqus software via applying periodic boundary conditions based on the mean volumetric stress. In the next step, the sandwich structure was subjected to impact loads at various speeds and contact force-time diagrams were plotted using Abaqus software. The modeled results were compared with the known experimental data which showed a high accuracy in predicting the mechanical properties and impact behavior of the nanocomposite sandwich structures. تفاصيل المقالة -
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42 - The Investigating and Simulating the Corona Phenomenon in The Power Transmission Lines of Power Networks Using the Finite Element Method
noushin dadashzadeh Elnaz poorreza Vahide MohadesiIn this article, the simulation of the physical phenomenon of coaxial corona discharge in air, in DC mode using the finite element method is discussed. Basically, to optimize the production process of ionized gas and any other physical phenomenon, we model and simulate أکثرIn this article, the simulation of the physical phenomenon of coaxial corona discharge in air, in DC mode using the finite element method is discussed. Basically, to optimize the production process of ionized gas and any other physical phenomenon, we model and simulate the phenomenon. To simulate this phenomenon, from two cylindrical electrodes, one inside (cathode) and the other outside (anode), the radius of the inner electrode is 100 microns and the distance between the electrodes is 10 cm. A constant voltage of 50 kV is applied to the inner electrode. The outer electrode is considered the ground. Our emphasis is on the formation of charged particles and their behavior in the resulting electric field. In order to avoid the complexity of the problem and save the simulation time, we model in a one-dimensional way and in the results extract the above phenomenon in a two-dimensional way. The gas temperature is 640 K and the air density is considered constant. تفاصيل المقالة -
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43 - تعیین توزیع حرارتی در پستهای کمپکت
میثم بهاروندترانسفورماتورها یکی از اجزاء مهم پست های کمپکت هستند و مطالعه رفتار مغناطیسی و حرارتی آنها در داخل پست های کمپکت، دارای اهمیت بسزائی می باشد. تعیین توزیع حرارتی در داخل ترانسفورماتورها بعلت پیچیدگی هندسی ساختمان ترانسفورماتور، وابسته بودن خواص مواد بکار رفته با درجه حرا أکثرترانسفورماتورها یکی از اجزاء مهم پست های کمپکت هستند و مطالعه رفتار مغناطیسی و حرارتی آنها در داخل پست های کمپکت، دارای اهمیت بسزائی می باشد. تعیین توزیع حرارتی در داخل ترانسفورماتورها بعلت پیچیدگی هندسی ساختمان ترانسفورماتور، وابسته بودن خواص مواد بکار رفته با درجه حرارت و غیرخطی بودن رفتار مغناطیسی آنها معمولا مشکل می باشد و پیچیده است. در این بین استفاده از روش های عددی همانند اجزاء محدود یک روش کارآمد برای تعیین توزیع حرارتی داخل ترانسفورمر و نیز تعیین حداکثر دمای سیم پیچی های ترانسفورمر می باشد. در این پایان نامه با استفاده از تحلیل های مغناطیسی و حرارتی دو بعدی اجزاء محدود توسط نرم افزار انسیس توزیع حرارتی سیم پیچی های ترانسفورمر در شرایط نرمال بهره برداری در فضای باز و نیز در شرایطی که ترانسفورمر در داخل پست کمپکت قرار دارد تعیین می شود و با توجه به اختلاف دمای حداکثر دمای سیم پیچ ها در دو شرایط، کلاس حرارتی پست کمپکت تعیین می شود. تفاصيل المقالة -
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44 - Numerical and Experimental Investigation on the Effect of Geometric Discontinuity on Frequency Response of Composite Lattice Conical Structures
M. R Zamani M ZaretabarComposite structures are increasingly being used in various engineering structures such as automotive, aerospace, and civil structures due to their superior properties, namely, high strength-to-weight ratio, impact resistance, and durability. For the purpose of accessib أکثرComposite structures are increasingly being used in various engineering structures such as automotive, aerospace, and civil structures due to their superior properties, namely, high strength-to-weight ratio, impact resistance, and durability. For the purpose of accessibility to other components and possibility of installation, aerospace structures encounters geometrical discontinuities which can lead to a complex structural analysis due to non-isotropic behavior. This paper aims to study the frequency response behavior of a composite lattice conical structure considering the effect of geometric discontinuity stiffened by a circular ring. The lattice structures are made of glass fiber reinforced polymers (GFRP) fabricated using filament winding method and cured in an autoclave. Numerical analysis and experimental modal testing was performed to obtain frequency response of the structures considering geometrical discontinuities. The results showed that the natural frequency values of structures with cutout in free-free boundary conditions are lower than those without cutout. Furthermore, comparing the mode shapes of structures indicated that these shapes were similar to each other and only some slight differences in discontinuity area were observed in some modes. Finally, the highest difference of numerical analysis results in structures with or without cutout was 2.61% while the highest difference of experimental analysis results in the structures was 3.73%. The greatest difference in the numerical and experimental analysis results is pertinent to the second mode in the structure without cutout is 15.64% and in the structure with cutout is 12.48%. تفاصيل المقالة -
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45 - Investigating the Effect of Joint Geometry of the Gas Tungsten Arc Welding Process on the Residual Stress and Distortion using the Finite Element Method
A Shiri A HeidariAlthough a few models have been proposed for 3D simulation of different welding processes, 2D models are still more effective in design goals, thus more popular due to the short-time analysis. In this research, replacing "time" by the "third dimension of place", the gas أکثرAlthough a few models have been proposed for 3D simulation of different welding processes, 2D models are still more effective in design goals, thus more popular due to the short-time analysis. In this research, replacing "time" by the "third dimension of place", the gas tungsten arc welding process was simulated by the finite element method in two dimensions and in a short time with acceptable accuracy in two steps (non-coupled thermal and mechanical analysis). A new method was proposed for applying initial conditions using temperature values calculated in the preceding step of the solution; this trick reduces nonlinear effects of birth of elements and considerably reduces analysis time. A new parameter was defined for determining thermal boundary conditions to determine the contribution of the imposed surface and volumetric thermal loads. The effect of weld joint geometry on residual stresses and distortion was studied based on a validated simulation program. Results suggest that changing the joint geometry from V-into X-groove, the maximum values of residual stress and distortion are reduced by 20% and 15%, respectively. تفاصيل المقالة -
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46 - Stress Concentration Factor of Single-Layered Graphene Sheets Containing Elliptical Vacancies
S.K Jalali M.J BeigrezaeeIn the present study, potential of finite element based molecular structural mechanics (MSM) for evaluating stress concentration factor of single-layered graphene sheets (SLGSs) with elliptical vacancies is successfully addressed. The MSM approach mimics the interatomic أکثرIn the present study, potential of finite element based molecular structural mechanics (MSM) for evaluating stress concentration factor of single-layered graphene sheets (SLGSs) with elliptical vacancies is successfully addressed. The MSM approach mimics the interatomic forces of the nanostructure by defining an equivalent frame structure containing beam elements. To obtain the mechanical and cross sectional properties of the equivalent beam, the potential energies of chemical bonds between carbon atoms in the hexagonal lattice of SLGSs are equaled to the strain energies of the beams. This novel proposed approach accurately predicts the stress concentration in graphene sheets with significantly less computational effort in comparison to computational physics methods. Both armchair and zigzag configurations are considered. Furthermore, a comparison between the results obtained by presented MSM approach and theory of elasticity for thin infinite panels having elliptical holes is presented. Influence of chirality, and geometry of elliptical vacancies are investigated in details. Results reveal that MSM approach can successfully predicts stress concentration factor phenomena in nano structures, especially SLGSs. It is seen that chirality has a significant effect on the stress concentration factor so that armchair SLGSs show a larger value of stress concentration. تفاصيل المقالة -
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47 - Studying the Mechanical and Thermal Properties of Polymer Nanocomposites Reinforced with Montmorillonite Nanoparticles Using Micromechanics Method
M.H Yas H Shahrani Korani F Zare JouneghaniIn this study, the mechanical and thermal behavior of the nano-reinforced polymer composite reinforced by Montmorillonite (MMT) nanoparticles is investigated. Due to low cost of computations, the 3D representative volume elements (RVE) method is utilized using ABAQUS fi أکثرIn this study, the mechanical and thermal behavior of the nano-reinforced polymer composite reinforced by Montmorillonite (MMT) nanoparticles is investigated. Due to low cost of computations, the 3D representative volume elements (RVE) method is utilized using ABAQUS finite element commercial software. Low density poly ethylene (LDPE) and MMT are used as matrix and nanoparticle material, respectively. By using various geometric shapes and weight fractions of nanoparticle, the mechanical and thermal properties such as Young’s modulus, shear modulus, heat expansion coefficient and heat transfer coefficient are studied. Due to addressing the properties of interfacial zone between the matrix and nanoparticle, finite element modeling is conducted in two ways, namely, perfect bonding and cohesive zone. The results are validated by comparing with experimental results reported in literature and a reasonable agreement was observed. The prediction function for Young’s modulus is presented by employing Genetic Algorithm (GA) method. Also, Kerner and Paul approaches as theoretical models are used to calculate the Young’s modulus. It was finally concluded that the magnitude of the Young’s and shear modules increase by adding MMT nanoparticles. Furthermore, increment of MMT nanoparticles to polymer matrix nanocomposite decrease the heat expansion and heat transfer coefficients. تفاصيل المقالة -
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48 - Influence of Addendum Modification Factor on Root Stresses in Normal Contact Ratio Asymmetric Spur Gears
R Prabhu Sekar R RavivarmanTooth root crack is considered as one of the crucial causes of failure in the gearing system and it occurs at the tooth root due to an excessive bending stress developed in the root region. The modern power transmission gear drives demand high bending load capacity, inc أکثرTooth root crack is considered as one of the crucial causes of failure in the gearing system and it occurs at the tooth root due to an excessive bending stress developed in the root region. The modern power transmission gear drives demand high bending load capacity, increased contact load capacity, low weight, reduced noise and longer life. These subsequent conditions are satisfied by the aid of precisely designed asymmetric tooth profile which turns out to be a suitable alternate for symmetric spur gears in applications like aerospace, automotive, gear pump and wind turbine industries. In all step up and step down gear drives (gear ratio > 1), the pinion (smaller in size) is treated as a vulnerable one than gear (larger in size) which is primarily due to the development of maximum root stress in the pinion tooth. This paper presents an idea to improve the bending load capacity of asymmetric spur gear drive system by achieving the same stresses between the asymmetric pinion and gear fillet regions which can be accomplished by providing an appropriate addendum modification. For this modified addendum the pinion and gear teeth proportion equations have been derived. In addition, the addendum modification factors required for a balanced maximum fillet stress condition has been determined through FEM for different parameters like drive side pressure angle, number of teeth and gear ratio. The bending load capacity of the simulated addendum modified asymmetric spur gear drives were observed to be prevalent (very nearly 7%) to that of uncorrected asymmetric gear drives. تفاصيل المقالة -
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49 - The Effects of Forming Parameters on the Single Point Incremental Forming of 1050 Aluminum Alloy Sheet
R SafdarianThe single point incremental forming (SPIF) is one of the dieless forming processes which is widely used in the sheet metal forming. The correct selection of the SPIF parameters influences the formability and quality of the product. In the present study, the Gurson-Tver أکثرThe single point incremental forming (SPIF) is one of the dieless forming processes which is widely used in the sheet metal forming. The correct selection of the SPIF parameters influences the formability and quality of the product. In the present study, the Gurson-Tvergaard Needleman (GTN) damage model was used for the fracture prediction in the numerical simulation of the SPIF process of aluminum alloy 1050. The GTN parameters of AA 1050 sheet were firstly identified by the numerical simulation of tensile test and comparison of the experimental and numerical stress-strain curves. The identified parameters of the GTN damage model were used for fracture prediction in the SPIF process. The numerical results of the fracture position, thickness variation across the sample and forming height were compared with the experimental results. The numerical results had good agreement with the experimental ones. The effect of SPIF main parameters was investigated on the formability of samples by the verified numerical model. These parameters were tool rotation speed, tool feed rate, tool diameter, wall angle of the sample, vertical pitch, and friction between the tool and the blank. تفاصيل المقالة -
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50 - Noise Effects on Modal Parameters Extraction of Horizontal Tailplane by Singular Value Decomposition Method Based on Output Only Modal Analysis
P Jalali S Varahram R Hassannejad M.H SadeghiAccording to the great importance of safety in aerospace industries, identification of dynamic parameters of related equipment by experimental tests in operating conditions has been in focus. Due to the existence of noise sources in these conditions the probability of f أکثرAccording to the great importance of safety in aerospace industries, identification of dynamic parameters of related equipment by experimental tests in operating conditions has been in focus. Due to the existence of noise sources in these conditions the probability of fault occurrence may increases. This study investigates the effects of noise in the process of modal parameters identification by Output only Modal Analysis (OMA) method using Singular Value Decomposition (SVD) algorithm. The study case is the horizontal tailplane of the aircraft; therefore, at first, the modal parameters of the tailplane are obtained numerically. Then a cantilever beam is used to perform experimental tests with regard to the high aspect ratio of the modeled tailplane. The modal parameters of the beam are obtained nonparametrically by Experimental Modal Analysis (EMA) and OMA. In order to investigate the effects of noise in a controlled manner, the artificial excitation namely the shaker with the random force is used. Then, the effects of noisy measurements on the specifications of the system in EMA and OMA methods are investigated. The results indicate that: 1. The OMA method has more resistance against the noise for extracting natural frequencies. 2. The results of the Modal Assurance Criterion (MAC) values by EMA method, in the condition of noise existence in output data, are worse than the noise existence in input data. 3. The average of MAC values in general condition of EMA method by noisy input & output data is worse than the OMA method. تفاصيل المقالة -
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51 - An Efficient Finite Element Formulation Based on Deformation Approach for Bending of Functionally Graded Beams
H Ziou M Himeur H Guenfoud M GuenfoudFinite element formulations based generally on classical beam theories such as Euler-Bernoulli or Timoshenko. Sometimes, these two formulations could be problematic expressed in terms of restrictions of Euler-Bernoulli beam theory, in case of thicker beams due to non-co أکثرFinite element formulations based generally on classical beam theories such as Euler-Bernoulli or Timoshenko. Sometimes, these two formulations could be problematic expressed in terms of restrictions of Euler-Bernoulli beam theory, in case of thicker beams due to non-consideration of transverse shear; phenomenon that is known as shear locking characterized the Timoshenko beam theory, in case of thin beams; problem of slow of convergence in regards to the element of Timoshenko beam. In responding to this problematic, a new beam finite element model is developed to study the static bending of functionally graded beams. The originality of this model lies in the use of a deformation approach with the consideration of a central node positioned in the middle of the beam. The degrees of freedom of this node are subsequently eliminated by the method of static condensation. In addition, this model is suitable for all linear structures regardless of L/h ratio. Functionally graded material beams have a smooth variation of material properties due to continuous change in micro structural details. The mechanical properties of the beam are assumed to vary continuously in the thickness direction by a simple power-law distribution in terms of the volume fractions of the constituents. A simply supported beam subjected to uniform load for different length-to-thickness ratio has been chosen in the analysis. Finite element solutions obtained with the new finite element model are presented, and the obtained results are evaluated with the existing solutions to verify the validity of the present model. تفاصيل المقالة -
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52 - Fatigue Crack Growth in Plastically Compressible Solids: Role of Negative Stress Ratio, Plastic Compressibility and Strain Softening
Y Mittal D Khan S Pandey G.Chand GuptaThe effect of cyclic loading on fatigue crack growth in plastically compressible solids is investigated at negative stress ratio under plane strain and small scale yielding conditions. The material is characterized by a finite strain elastic viscoplastic constitutive mo أکثرThe effect of cyclic loading on fatigue crack growth in plastically compressible solids is investigated at negative stress ratio under plane strain and small scale yielding conditions. The material is characterized by a finite strain elastic viscoplastic constitutive model with hardening and hardening-softening-hardening hardness functions. Displacements corresponding to the isotropic linear elastic mode I crack field are prescribed on a remote boundary. The plastic crack growth, crack tip opening displacement (CTOD) and near crack tip stress fields are presented using finite element method. Material hardening/ softening has a major relevance on crack growth, CTOD and the evolution of stress distribution. It is revealed here that the negative stress ratio can significantly influence the loading conditions at the crack tip and thereby increase the crack growth for tension–compression loading for hardening material whereas the fatigue crack growth of plastically compressible hardening-softening-hardening material is only slightly affected by the negative stress ratio albeit it is accepted in literature that compressive loads contribute to fatigue crack growth significantly. In the present studies, the CTOD variation with applied load and the near stress distribution are also very unusual in nature. تفاصيل المقالة -
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53 - A New Numerical Study Method of Thermal Stress Distribution and Tortuosity Effectiveness in an Anode Porous Electrode for a Planar Solid Oxide Fuel Cell
I.E Fahs M GhasemiA fuel cell is an electro-chemical tool capable of converting chemical energy into electricity. High operating temperature of solid oxide fuel cell, between 700oC to 1000oC, causes thermal stress. Thermal stress causes gas escape, structure variability and cease operati أکثرA fuel cell is an electro-chemical tool capable of converting chemical energy into electricity. High operating temperature of solid oxide fuel cell, between 700oC to 1000oC, causes thermal stress. Thermal stress causes gas escape, structure variability and cease operation of the SOFC before its lifetime.The purpose of the current paper is to present a method that predicts the thermal stress distribution in an anisotropic porous anode of planar SOFC. The coupled governing non-linear differential equations, heat transfer, fluid flow, mass transfer, mass continuity, and momentum are solved numerically. A code based oncomputational fluid dynamics (CFD), computational structural mechanics and finite element method (FEM) is developed and utilized. The code uses the generated data inside the porous anode in order to detect the temperature and the stress distribution using the Darcy’s law and the Navier-Stokes equations. The numerical results used to govern the areas of high values of stresses were higher than the yield strength of materials. The results show that a highest thermal stress occurs at lower corners of the anode. The concentrated temperature occurs at the middle of the electrolyte-anode whereas the maximum pressure occurs at the middle of the upper and lower section of the anode. تفاصيل المقالة -
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54 - Vibration of Timoshenko Beam-Soil Foundation Interaction by Using the Spectral Element Method
S Hamioud S Khalfallah S BoudaaThis article presents an analysis of free vibration of elastically supported Timoshenko beams by using the spectral element method. The governing partial differential equation is elaborated to formulate the spectral stiffness matrix. Effectively, the non classical end b أکثرThis article presents an analysis of free vibration of elastically supported Timoshenko beams by using the spectral element method. The governing partial differential equation is elaborated to formulate the spectral stiffness matrix. Effectively, the non classical end boundary conditions of the beam are the primordial task to calibrate the phenomenon of the Timoshenko beam-soil foundation interaction. Non-dimensional natural frequencies and shape modes are obtained by solving the partial differential equations, numerically. Upon solving the eigenvalue problem, non-dimensional frequencies are computed for the first three modes of vibration. Obtained results of this study are intended to describe multiple objects, such as: (1) the establishment of the modal analysis with and without elastic springs, (2) the quantification of the influence of the beam soil foundation interaction, (3) the influence of soil foundation stiffness’ on free vibration characteristics of Timoshenko beam. For this propose, the first three eigenvalues of Timoshenko beam are calculated and plotted for various stiffness of translational and rotational springs. تفاصيل المقالة -
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55 - On Validity of Analytical Method in Cracked Column Post-Buckling Analysis Using Empirical and Numerical Investigations
K Salmalian A Alijani H Ramezannejad AzarboniThe three analytical, finite element and experimental methods are applied to study the nonlinear buckling of cracked columns. The original aim of this research is to investigate the validity of the common analytical method in an analogy with the experimental method and أکثرThe three analytical, finite element and experimental methods are applied to study the nonlinear buckling of cracked columns. The original aim of this research is to investigate the validity of the common analytical method in an analogy with the experimental method and the finite element method of MATLAB programming-based. The literature review shows that papers applied this analytical method without considering its drawbacks to determine the post-buckling results. Results in the linear part of the analytical method are in close accordance with the two others, while a clear difference in the nonlinear part of the analytical method is observed with the actual results obtained from the experimental tests and numerical results of the finite element method. An in-depth discussion is represented to find out the main reasons of this difference. The conversion matrix technique in the finite element method and dividing the column into two segments in the analytical method are used to include the crack parameters in relations according to the continuity conditions in the crack tip. An investigation is performed to study the effect of the crack depth and position on the critical buckling load and the post-buckling path. تفاصيل المقالة -
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56 - Static Analysis and Fatigue of DHS Implants to Treatment Femoral and Intertrochanteric Neck Fractures Using Ti6Al4V and SS316 Alloys, A Finite Element Analysis
A Shokrgozar Navi S Etemadi Haghighi M Haghpanahi A MomeniThe neck fractures and the femurs intertrochanteric are common complications that are recovered by a multicomponent implant called dynamic hip screw (DHS). In the present study, a standard four-hole DHS with Ti6Al4V (Ti6) and SS316l (SS) alloys for static mode (slow wal أکثرThe neck fractures and the femurs intertrochanteric are common complications that are recovered by a multicomponent implant called dynamic hip screw (DHS). In the present study, a standard four-hole DHS with Ti6Al4V (Ti6) and SS316l (SS) alloys for static mode (slow walking) and fatigue mode like normal walking (NW), descending stairs (DS), and falling (FA) by finite elements analysis (FEA) have been evaluated (ANSYS software). The results have been confirmed by similar studies in static mode and maximum Von Mises stress and strain are obtained for Ti6 about 145MPa and 0.191%, and SS about 196 MPa and 0.121%. Most critical stress points occur in cortical screws, plate holes, compression screws, and lag screws, respectively. DHS components with Ti6 alloy have infinite life in NW and DS, also in FA, they have a finite life (107-108 cycle) with alternating Von Mises stress () ~ 425 MPa, while for SS they have finite life in all activities, which NW ~107 cycle, DS~106 cycle,and even in FA cortical screw life of failure reaches to 98 cycles and . The critical regions are the same as the failure regions common in biomechanical and clinical studies. These regions are mainly concentration stress points that lead to DHS failure as the crack grows. تفاصيل المقالة -
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57 - Fatigue Life Assessment for an Aluminum Alloy Piston Using Stress Gradient Approach Described in the FKM Method
H AshouriEngine piston is one of the most complex components among all automotive. The engine can be called the heart of a car and the piston may be considered the most important part of an engine. In fact, piston has to endure thermo-mechanical cyclic loadings in a wide range o أکثرEngine piston is one of the most complex components among all automotive. The engine can be called the heart of a car and the piston may be considered the most important part of an engine. In fact, piston has to endure thermo-mechanical cyclic loadings in a wide range of operating conditions. This paper presents high cycle fatigue (HCF) life prediction for an aluminum alloy piston using stress gradient approach described in the Forschungskuratorium Maschinenbau (FKM) method. For this purpose, first Solidworks software was used to model the piston. Then Ansys Workbench software was used to determine temperature and stress distribution of the piston. Finally, in order to study the fatigue life of the piston based on HCF approach, the results were fed into the nCode Design Life software. The numerical results showed that the temperature maximum occurred at the piston crown center. The results of finite element analysis (FEA) indicated that the stress and number of cycles to failure have the most critical values at the upper portion of piston pin and piston compression grooves. To evaluate properly of results, stress analysis and HCF results is compared with real samples of damaged piston and it has been shown that critical identified areas, match well with areas of failure in the real samples. The lifetime of this part can be determined through FEA instead of experimental tests. تفاصيل المقالة -
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58 - Fatigue Life Analysis of the Propeller Shafting System of a VLCC Ship Powertrain System Using Finite Element or Distributed-Lumped Methods
A Gholami S. A Jazayeri Q EsmailiIn this study, the dynamic behavior of the propulsion system of a VLCC (Very Large Crude oil Carrier) ship is investigated using a multi-input multi-output model. In this system the engine ordered speed and the number of active cylinders are assumed as inputs and the dy أکثرIn this study, the dynamic behavior of the propulsion system of a VLCC (Very Large Crude oil Carrier) ship is investigated using a multi-input multi-output model. In this system the engine ordered speed and the number of active cylinders are assumed as inputs and the dynamic parameters of the engine such as torque and speed are considered as outputs. In this research, the effects of sea wave and wind on the system dynamic behavior have been investigated. In addition, the ship powertrain system is investigated in which the intermediate shaft and propeller shaft are analyzed using lumped parameter method, finite element method, distributed-lumped method and the results of these modeling techniques are compared to the modeling results in which the connecting shafts were considered as rigid body. Comparison of the results shows that there are significant differences between the results of rigid body method and other three types of system modeling. On the other hand, the time required to run the distributed-lumped model is much shorter compared to other methods that are considered in the study for the dynamic behavior of the ship's powertrain systems. On the other hand, the fatigue analysis of the ship power transmission shafts shows that the fatigue life assessment of these shafts is of great importance and should be considered in the design phase. تفاصيل المقالة -
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59 - New Two 20-Node High-Order Finite Elements Based on the SFR Concept for Analyzing 3D Elasticity Problems
H Djahara K Meftah L Sedira A AyadiThis paper proposes conforming and nonconforming 20-node hexahedral finite elements. The elements’ formulation stems from the so-called Space Fiber Rotation (SFR) concept, allowing a spatial rotation of three-dimensional virtual fiber within the elements. Adding r أکثرThis paper proposes conforming and nonconforming 20-node hexahedral finite elements. The elements’ formulation stems from the so-called Space Fiber Rotation (SFR) concept, allowing a spatial rotation of three-dimensional virtual fiber within the elements. Adding rotational degrees of freedom results in six degrees of freedom per node (three rotations and three translations) which enhances the approximation of the classical displacement field. The incompatible modes approach has been adopted in the nonconforming element formulation in order to avoid numerical deficiencies associated with the Poisson’s ratio locking phenomenon. The accuracy of the proposed elements is examined through a series of three-dimensions linear elastic benchmarks including beam, plates, and shell structures. The proposed elements were shown to give better results than the standard 20-node hexahedron especially when mesh distortion is applied. This confirms that the two proposed elements are less sensitive to mesh distortion. The elements also show good performance when compared with analytical and numerical solutions from the literature. تفاصيل المقالة -
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60 - Mixed-Mode Stress Intensity Factors for Surface Cracks in Functionally Graded Materials Using Enriched Finite Elements
J Sheikhi M Poorjamshidian S PeymanThree-dimensional enriched finite elements are used to compute mixed-mode stress intensity factors (SIFs) for three-dimensional cracks in elastic functionally graded materials (FGMs) that are subject to general mixed-mode loading. The method, which advantageously does n أکثرThree-dimensional enriched finite elements are used to compute mixed-mode stress intensity factors (SIFs) for three-dimensional cracks in elastic functionally graded materials (FGMs) that are subject to general mixed-mode loading. The method, which advantageously does not require special mesh configuration/modifications and post-processing of finite element results, is an enhancement of previous developments applied so far on isotropic homogeneous and isotropic interface cracks. The spatial variation of FGM material properties is taken into account at the level of element integration points. To validate the developed method, two- and three-dimensional mixed-mode fracture problems are selected from the literature for comparison. Two-dimensional cases include: inclined central crack in a large FGM medium under uniform tensile strain loading and an edge crack in a finite-size plate under shear traction load. The three-dimensional example models a deflected surface crack in a finite-size FGM plate under uniform tensile stress loading. Comparisons between current results and those from analytical and other numerical methods yield good agreement. Thus, it is concluded that the developed three-dimensional enriched finite elements are capable of accurately computing mixed-mode fracture parameters for cracks in FGMs. تفاصيل المقالة -
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61 - Multiscale Analysis of Transverse Cracking in Cross-Ply Laminated Beams Using the Layerwise Theory
W Jin Na J.N ReddyA finite element model based on the layerwise theory is developed for the analysis of transverse cracking in cross-ply laminated beams. The numerical model is developed using the layerwise theory of Reddy, and the von Kármán type nonlinear strain field is أکثرA finite element model based on the layerwise theory is developed for the analysis of transverse cracking in cross-ply laminated beams. The numerical model is developed using the layerwise theory of Reddy, and the von Kármán type nonlinear strain field is adopted to accommodate the moderately large rotations of the beam. The finite element beam model is verified by comparing the present numerical solutions with the elasticity solutions available in the literature; an excellent agreement is found. The layerwise beam model is then used to investigate the influence of transverse cracks on material properties and the response in cross-ply laminates using a multiscale approach. The multiscale analysis consists of numerical simulations at two different length scales. In the first scale, a mesoscale, a systematic procedure to quantify the stiffness reduction in the cracked ply is proposed exploiting the laminate theory. In the second scale, a macroscale, continuum damage mechanics approach is used to compute homogenized material properties for a unit cell, and the effective material properties of the cracked ply are extracted by the laminate theory. In the macroscale analysis, a beam structure under a bending load is simulated using the homogenized material properties in the layerwise finite element beam model. The stress redistribution in the beam according to the multiplication of transverse cracks is taken into account and a prediction of sequential matrix cracking is presented. تفاصيل المقالة -
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62 - Thermal Vibration of Composites and Sandwich Laminates Using Refined Higher Order Zigzag Theory
A Chakrabarti S.K Singh A.H SheikhVibration of laminated composite and sandwich plate under thermal loading is studied in this paper. A refined higher order theory has been used for the purpose. In order to avoid stress oscillations observed in the implementation of a displacement based finite element, أکثرVibration of laminated composite and sandwich plate under thermal loading is studied in this paper. A refined higher order theory has been used for the purpose. In order to avoid stress oscillations observed in the implementation of a displacement based finite element, the stress field derived from temperature (initial strains) have been made consistent with total strain field. So far no study has been reported in literature on the thermal vibration problem based on the refined higher order theory using a FE model. Numerical results are presented for thermal vibration problems to study the influence of boundary conditions, ply orientation and plate geometry on the natural frequencies of these structures. تفاصيل المقالة -
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63 - Buckling Analysis of Rectangular Functionally Graded Plates with an Elliptic Hole Under Thermal Loads
R Rezae A.R Shaterzadeh S AbolghasemiThis paper presents thermal buckling analysis of rectangular functionally graded plates (FG plates) with an eccentrically located elliptic cutout. The plate governing equations derived by the first order shear deformation theory (FSDT) and finite element formulation is أکثرThis paper presents thermal buckling analysis of rectangular functionally graded plates (FG plates) with an eccentrically located elliptic cutout. The plate governing equations derived by the first order shear deformation theory (FSDT) and finite element formulation is developed to analyze the plate behavior subjected to a uniform temperature rise across plate thickness. It is assumed that the non-homogenous material properties vary through the plate thickness according to a power function. The developed finite element (FE) code with an extended mesh pattern is written in MATLAB software. The effects of aspect ratio of the plate, ellipse radii ratio, position and orientation of the cutout, boundary conditions (BCs) and volume fraction exponent are investigated in details. The results of present code are compared with those available in the literature and some useful design-orientated conclusions are achieved. تفاصيل المقالة -
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64 - Creep Life Forecasting of Weldment
J Jelwan M Chowdhry G PearceOne of the yet unresolved engineering problems is forecasting the creep lives of weldment in a pragmatic way with sufficient accuracy. There are number of obstacles to circumvent including: complex material behavior, lack of accurate knowledge about the creep material b أکثرOne of the yet unresolved engineering problems is forecasting the creep lives of weldment in a pragmatic way with sufficient accuracy. There are number of obstacles to circumvent including: complex material behavior, lack of accurate knowledge about the creep material behavior specially about the heat affected zones (HAZ),accurate and multi-axial creep damage models, etc. In general, creep life forecasting may be categorized into two groups, viz., those that are based on microscopic modeling and others that are based on macroscopic (phemenological) concepts. Many different micro-structural processes may cause creep damage .The micro-structural processes highlight the fact that the creep damages can be due to cavity nucleation and growth. Dislocation creep is another mechanism with micro-structural features such as sub-grain formation and growth, new phase formation, such as the Z phase, coarsening leading to the dissolution of the MX phase. This leads to the removal of pinning precipitates, which allow local heterogeneous sub-grain growth, weakening due to this growth and also to the dissolution of the MX. These features normally lead to the earlier formation of tertiary creep and reduced life. Considering welded joints ,the development of models for practical yet sufficiently accurate creep life forecasting based on micro-structural modeling becomes even more complicated due to variation of material in the base, weld and heat-affected-zone (HAZ) and variation of the micro-structure within HAZ and their interactions. So far, and until this date, none of the micro-structural models can forecast the creep life of industrial components with sufficient accuracy in an economic manner. There are several macroscopic (phemenological) models for creep life forecasting, including: time-fraction rule, strain-fraction rule, the reference stress and skeletal stress method, continuum damage model, etc. Each of which has their own limitations .This paper gauges to a multi-axial yet pragmatic and simple model for creep life forecasting weldment operating at high temperature and subjected to an elastic-plastic-creep deformation. تفاصيل المقالة -
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65 - Analytical and Numerical Investigation of FGM Pressure Vessel Reinforced by Laminated Composite Materials
A.R Ghasemi A Kazemian M MoradiIn this research, the analytical and numerical investigation of a cylindrical shell made of functionally graded materials (FGMs) reinforced by laminated composite subjected to internal pressure is presented. Using the infinitesimal theory of elasticity, the analytical s أکثرIn this research, the analytical and numerical investigation of a cylindrical shell made of functionally graded materials (FGMs) reinforced by laminated composite subjected to internal pressure is presented. Using the infinitesimal theory of elasticity, the analytical solution of stress and strain in vessels made of FGMs is studied first. It is assumed that the elasticity modulus follows a power law distribution in the thickness direction and Poisson's ratio considered to be constant for simplicity. The results of the finite element method using ABAQUS software for in-homogeneity constant in the range of -2 to 2 have been compared with the analytical results. The comparison represents good coincidence between analytical and numerical results and confirms the accuracy of stress and strain solutions presented for vessel made of FGMs. The stress and strain solutions in laminated composite vessels are then investigated. Finally, modeling of FGM vessel reinforced by composite laminates with different lay-up is taken into consideration. The obtained results demonstrate that in the cylindrical shell reinforced by laminated composites, the maximum stress is considerably less than the maximum stress in the pressure vessels made of just composites or FGMs. تفاصيل المقالة -
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66 - Hygrothermal Analysis of Laminated Composite Plates by Using Efficient Higher Order Shear Deformation Theory
S.K Singh A ChakrabartiHygrothermal analysis of laminated composite plates has been done by using an efficient higher order shear deformation theory. The stress field derived from hygrothermal fields must be consistent with total strain field in this type of analysis. In the present formulati أکثرHygrothermal analysis of laminated composite plates has been done by using an efficient higher order shear deformation theory. The stress field derived from hygrothermal fields must be consistent with total strain field in this type of analysis. In the present formulation, the plate model has been implemented with a computationally efficient C0 finite element developed by using consistent strain field. Special steps are introduced to circumvent the requirement of C1coninuity in the original plate formulation and C0 continuity of the present element has been compensated in stiffness matrix calculations. The accuracy of the proposed C0 element is established by comparing the results with those obtained by three dimensional elasticity solutions and other finite element analysis. تفاصيل المقالة -
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67 - Nonlinear Finite Element Analysis of Bending of Straight Beams Using hp-Spectral Approximations
R RanjanDisplacement finite element models of various beam theories have been developed using traditional finite element interpolations (i.e., Hermite cubic or equi-spaced Lagrange functions). Various finite element models of beams differ from each other in the choice of the in أکثرDisplacement finite element models of various beam theories have been developed using traditional finite element interpolations (i.e., Hermite cubic or equi-spaced Lagrange functions). Various finite element models of beams differ from each other in the choice of the interpolation functions used for the transverse deflection w, total rotation φ and/or shear strain γxz, or in the integral form used (e.g., weak form or least-squares) to develop the finite element model. The present study is concerned with the development of alternative beam finite elements using hp-spectral nodal expansions to eliminate shear and membrane locking. Both linear and non-linear analysis are carried out using both displacement and mixed finite element models of the beam theories studied. Results obtained are compared with both analytical (series) solutions and non-linear finite element solutions from literature, and excellent agreement is found for all cases. تفاصيل المقالة -
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68 - A Comparative Study of Least-Squares and the Weak-Form Galerkin Finite Element Models for the Nonlinear Analysis of Timoshenko Beams
W Kim J.N ReddyIn this paper, a comparison of weak-form Galerkin and least-squares finite element models of Timoshenko beam theory with the von Kármán strains is presented. Computational characteristics of the two models and the influence of the polynomial orders used on أکثرIn this paper, a comparison of weak-form Galerkin and least-squares finite element models of Timoshenko beam theory with the von Kármán strains is presented. Computational characteristics of the two models and the influence of the polynomial orders used on the relative accuracies of the two models are discussed. The degree of approximation functions used varied from linear to the 5th order. In the linear analysis, numerical results of beam bending under different types of boundary conditions are presented along with exact solutions to investigate the degree of shear locking in the newly developed mixed finite element models. In the nonlinear analysis, convergences of nonlinear finite element solutions of newly developed mixed finite element models are presented along with those of existing traditional model to compare the performance. تفاصيل المقالة -
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69 - An Experimental and Numerical Study of Forming Limit Diagram of Low Carbon Steel Sheets
M Kadkhodayan H AleyasinThe forming limit diagram (FLD) is probably the most common representation of sheet metal formability and can be defined as the locus of the principal planar strains where failure is most likely to occur. Low carbon steel sheets have many applications in industries, esp أکثرThe forming limit diagram (FLD) is probably the most common representation of sheet metal formability and can be defined as the locus of the principal planar strains where failure is most likely to occur. Low carbon steel sheets have many applications in industries, especially in automotive parts, therefore it is necessary to study the formability of these steel sheets. In this paper, FLDs, were determined experimentally for two grades of low carbon steel sheets using out-of-plane (dome) formability test. The effect of different parameters such as work hardening exponent (n), anisotropy (r) and thickness on these diagrams were studied. In addition, the out-of-plane stretching test with hemispherical punch was simulated by finite element software Abaqus. The limit strains occurred with localized necking were specified by tracing the thickness strain and its first and second derivatives versus time at the thinnest element. Good agreement was achieved between the predicted data and the experimental data. تفاصيل المقالة -
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70 - Nonlinear Finite Element Eccentric Low-Velocity Impact Analysis of Rectangular Laminated Composite Plates Subjected to In-phase/Anti-phase Biaxial Preloads
M Shariyat M Moradi S SamaeeAll impact analyses performed so far for the composite plates, have treated central impacts. Furthermore, investigations on influences of the in-plane biaxial compression, tension, or tension-compression preloads on various responses of the low-velocity impact, especial أکثرAll impact analyses performed so far for the composite plates, have treated central impacts. Furthermore, investigations on influences of the in-plane biaxial compression, tension, or tension-compression preloads on various responses of the low-velocity impact, especially the indentation, have not been performed so far. In the present research, a finite element formulation is presented for response prediction of a low-velocity eccentric impact between a rigid spherical indenter and a laminated composite rectangular plate with asymmetric lamination scheme. Different contact laws are considered for the loading and unloading phases. A parametric study is performed to investigate influence of the specifications of the plates and the indenter, the eccentric value, and the in-plane preloads on the indentation and force time histories. Results show that the compressive and tensile in-plane preloads reduce and increase the contact force (and consequently, the indentation values), respectively. Therefore, the extensive tensile preloads may lead to higher damages. تفاصيل المقالة -
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71 - A New Eight Nodes Brick Finite Element Based on the Strain Approach
Kh Guerraiche L Belounar L BouzidiIn this paper, a new three dimensional brick finite element based on the strain approach is presented with the purpose of identifying the most effective to analyze linear thick and thin plate bending problems. The developed element which has the three essential external أکثرIn this paper, a new three dimensional brick finite element based on the strain approach is presented with the purpose of identifying the most effective to analyze linear thick and thin plate bending problems. The developed element which has the three essential external degrees of freedom (U, V and W) at each of the eight corner nodes, is used with a modified elasticity matrix in order to satisfy the basic hypotheses of the theory of plates. The displacements field of the developed element is based on assumed functions for the various strains satisfying the compatibility and the equilibrium equations. New and efficient formulations of this element is discussed in detail, and the results of several examples related to thick and thin plate bending in linear analysis are used to demonstrate the effectiveness of the proposed element. The linear analyses using this developed element exhibit an excellent performance over a set of problems. تفاصيل المقالة -
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72 - Dynamic Fracture Analysis Using an Uncoupled Arbitrary Lagrangian Eulerian Finite Element Formulation
A.R Shahani M.R AminiThis paper deals with the implementation of an efficient Arbitrary Lagrangian Eulerian (ALE) formulation for the three dimensional finite element modeling of mode I self-similar dynamic fracture process. Contrary to the remeshing technique, the presented algorithm can c أکثرThis paper deals with the implementation of an efficient Arbitrary Lagrangian Eulerian (ALE) formulation for the three dimensional finite element modeling of mode I self-similar dynamic fracture process. Contrary to the remeshing technique, the presented algorithm can continuously advance the crack with the one mesh topology. The uncoupled approach is employed to treat the equations. So, each time step is split into two phases: an updated Lagrangian phase followed by an Eulerian phase. The implicit time integration method is applied for solving the transient problem in Lagrangian phase with no convective effects. A mesh motion scheme, in which the related equations need not to be solved at every time step, is proposed in Eulerian phase. The critical dynamic stress intensity factor criterion is used to determine the crack velocity. The variation of dynamic stress intensity factor along the crack front is also studied based on the interaction integral method. The proposed algorithm is applied to investigate the dynamic crack propagation in the DCB specimen subjected to fixed displacement. The predicted results are compared with the experimental study cited in the literature and a good agreement is shown. The proposed algorithm leads to the accurate and efficient analysis of dynamic crack propagation process. تفاصيل المقالة -
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73 - Finite Element Modeling of Crack Initiation Angle Under Mixed Mode (I/II) Fracture
S.S Bhadauria K.K Pathak M.S HoraPresent study deals with the prediction of crack initiation angle for mixed mode (I/II) fracture using finite element techniques and J-Integral based approach. The FE code ANSYS is used to estimate the stress intensity factor numerically. The estimated values of SIF wer أکثرPresent study deals with the prediction of crack initiation angle for mixed mode (I/II) fracture using finite element techniques and J-Integral based approach. The FE code ANSYS is used to estimate the stress intensity factor numerically. The estimated values of SIF were incorporated into six different crack initiation angle criteria to predict the crack initiation angle. Single edge crack specimens of Araldite-Hardener were used for the present analysis. Load was applied up to critical limit of the specimens containing crack at different angles of inclination. The crack initiation angle obtained using stress intensity factor and J-integral based approach were found close to each other and also found to be in good agreement with the available experimental results in literature. It is also investigated that as crack inclination angle increases material was found to behave in a brittle manner. تفاصيل المقالة -
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74 - hp-Spectral Finite Element Analysis of Shear Deformable Beams and Plates
R Ranjan J.N ReddyThere are different finite element models in place for predicting the bending behavior of shear deformable beams and plates. Mostly, the literature abounds with traditional equi-spaced Langrange based low order finite element approximations using displacement formulatio أکثرThere are different finite element models in place for predicting the bending behavior of shear deformable beams and plates. Mostly, the literature abounds with traditional equi-spaced Langrange based low order finite element approximations using displacement formulations. However, the finite element models of Timoshenko beams and Mindlin plates with linear interpolation of all generalized displacements have suffered from shear locking, which has been alleviated with the help of primarily reduced/selective integration techniques to obtain acceptable solutions [1-4]. These kinds of 'fixes' have come into existence because the element stiffness matrix becomes excessively stiff with low-order interpolation functions. In this study we propose an alternative spectrally accurate hp/spectral method to model the Timoshenko beam theory and first order shear deformation theory of plates (FSDT) to eliminate shear and membrane locking. Beams and isotropic and orthotropic plates with clamped and simply supported boundary conditions are analyzed to illustrate the accuracy and robustness of the developed elements. Full integration scheme is employed for all cases. The results are found to be in excellent agreement with those published in literature. تفاصيل المقالة -
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75 - Dynamics Analysis of the Steady and Transient States of a Nonlinear Piezoelectric Beam by a Finite Element Method
M Jabbari M Ghayour H.R MirdamadiThis paper presents a finite element formulation for the dynamics analysis of the steady and transient states of a nonlinear piezoelectric beam. A piezoelectric beam with damping is studied under harmonic excitation. A numerical method is used for this analysis. In the أکثرThis paper presents a finite element formulation for the dynamics analysis of the steady and transient states of a nonlinear piezoelectric beam. A piezoelectric beam with damping is studied under harmonic excitation. A numerical method is used for this analysis. In the paper, the central difference formula of four order is used and compared with the central difference formula of two order in the time response of the structure. The NPBDA program is developed with Matlab software. In this program, the Newmark technique for dynamic analysis is used, the Newton-Raphson iterative and Simpson methods are used for the nonlinear solution. To verify the NPBDA results, the experimental results of Malatkar are used for the nonlinear vibration analysis of a beam without piezoelectric properties. Then, the piezoelectric effect on the frequency mode values and the time response are obtained. Afterwards, the modulation frequency in the nonlinear beam and the piezoelectric effect in this parameter are verified. تفاصيل المقالة -
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76 - Investigation of Vacancy Defects on the Young’s Modulus of Carbon Nanotube Reinforced Composites in Axial Direction via a Multiscale Modeling Approach
M.R Davoudabadi S.D FarahaniIn this article, the influence of various vacancy defects on the Young’s modulus of carbon nanotube (CNT) - reinforcement polymer composite in the axial direction is investigated via a structural model in ANSYS software. Their high strength can be affected by the أکثرIn this article, the influence of various vacancy defects on the Young’s modulus of carbon nanotube (CNT) - reinforcement polymer composite in the axial direction is investigated via a structural model in ANSYS software. Their high strength can be affected by the presence of defects in the nanotubes used as reinforcements in practical nanocomposites. Molecular structural mechanics (MSM)/finite element (FE) Multiscale modeling of carbon nanotube/polymer composites with linear elastic polymer matrix is used to study the effect of CNT vacancy defects on the mechanical properties. The nanotube is modeled at the atomistic scale using MSM, where as the interface we assumed to be bonded by Vander Waals interactions based on the Lennar-Jonze potential at the interface and polymer matrix. A nonlinear spring is used for modeling of interactions. It is studied for zigzag and armchair Nanotubes with various aspect ratios (Length/Diameter). Finally, results of the present structural model show good agreement between our model and the experimental work. تفاصيل المقالة -
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77 - Prediction of Crack Initiation Direction for Inclined Crack Under Biaxial Loading by Finite Element Method
P.C Gope S.P Sharma A.K SrivastavaThis paper presents a simple method based on strain energy density criterion to study the crack initiation angle by finite element method under biaxial loading condition. The crack surface relative displacement method is used to eliminate the calculation of the stress i أکثرThis paper presents a simple method based on strain energy density criterion to study the crack initiation angle by finite element method under biaxial loading condition. The crack surface relative displacement method is used to eliminate the calculation of the stress intensity factors which are normally required. The analysis is performed using higher order four node quadrilateral element. The results by finite element method are compared with DET (determinant of stress tensor criterion) and strain energy density criteria. Finite element results are in well agreement with the experimental and analytical results. تفاصيل المقالة -
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78 - A New Finite Element Formulation for Buckling and Free Vibration Analysis of Timoshenko Beams on Variable Elastic Foundation
A Mirzabeigy M Haghpanahi R MadoliatIn this study, the buckling and free vibration of Timoshenko beams resting on variable elastic foundation analyzed by means of a new finite element formulation. The Winkler model has been applied for elastic foundation. A two-node element with four degrees of freedom is أکثرIn this study, the buckling and free vibration of Timoshenko beams resting on variable elastic foundation analyzed by means of a new finite element formulation. The Winkler model has been applied for elastic foundation. A two-node element with four degrees of freedom is suggested for finite element formulation. Displacement and rotational fields are approximated by cubic and quadratic polynomial interpolation functions, respectively. The length of the element is assumed to be so small, so that linear variation could be considered for elastic foundation through the length of the element. By these assumptions and using energy method, stiffness matrix, mass matrix and geometric stiffness matrix of the proposed beam element are obtained and applied to buckling and free vibration analysis. Accuracy of obtained formulation is approved by comparison with the special cases of present problem in other studies. Present formulation shows faster convergence in comparison with conventional finite element formulation. The effects of different parameters on the stability and free vibration of Timoshenko beams investigated and results are completely new. تفاصيل المقالة -
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79 - Bending Analysis of Composite Sandwich Plates with Laminated Face Sheets: New Finite Element Formulation
M.O Belarbi A TatiThe bending behavior of composites sandwich plates with multi-layered laminated face sheets has been investigated, using a new four-nodded rectangular finite element formulation based on a layer-wise theory. Both, first order and higher-order shear deformation; theories أکثرThe bending behavior of composites sandwich plates with multi-layered laminated face sheets has been investigated, using a new four-nodded rectangular finite element formulation based on a layer-wise theory. Both, first order and higher-order shear deformation; theories are used in order to model the face sheets and the core, respectively. Unlike any other layer-wise theory, the number of degrees of freedom in this present model is independent of the number of layers. The compatibility conditions as well as the displacement continuity at the interface ‘face sheets–core’ are satisfied. In the proposed model, the three translation components are common for the all sandwich layers, and are located at the mid-plane of the sandwich plate. The obtained results show that the developed model is able to give accurate transverse shear stresses directly from the constitutive equations. Moreover, a parametric study was also conducted to investigate the effect of certain characteristic parameters (core thickness to total thickness ratio, side-to-thickness ratio, boundary conditions, plate aspect ratio, core-to-face sheet anisotropy ratio, core shear modulus to the flexural modulus ratio and degree of orthotropy of the face sheet) on the transverse displacement variation. The numerical results obtained by our model are compared favorably with those obtained via analytical solution and numerical/experimental, results obtained by other models. The results obtained from this investigation will be useful for a more comprehensive understanding of the behavior of sandwich laminates. تفاصيل المقالة -
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80 - A Rapidly Convergent Nonlinear Transfinite Element Procedure for Transient Thermoelastic Analysis of Temperature-Dependent Functionally Graded Cylinders
M ShariyatIn the present paper, the nonlinear transfinite element procedure recently published by the author is improved by introducing an enhanced convergence criterion to significantly reduce the computational run-times. It is known that transformation techniques have been deve أکثرIn the present paper, the nonlinear transfinite element procedure recently published by the author is improved by introducing an enhanced convergence criterion to significantly reduce the computational run-times. It is known that transformation techniques have been developed mainly for linear systems, only. Due to using a huge number of time steps, employing the conventional time integration methods requires quite huge computational time and leads to remarkable error accumulation, numerical instability, or numerical damping, especially for long investigation times. The present method specially may be extended to problems where the required time steps are of the order of the round-off errors (e.g., coupled thermoelasticty problems). The present procedure is employed for transient thermoelastic analysis of thick-walled functionally graded cylinders with temperature-dependent material properties, as an example. To reduce the effect of the artificial local heat and stress shock source generation at the mutual boundaries of the elements, second order elements are used. Influences of various parameters on the temperature and stress distributions are investigated. Furthermore, results of the proposed transfinite element technique are compared with the results obtained by other references to verify the validity, accuracy, and efficiency of the proposed method. تفاصيل المقالة -
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81 - On the Analysis of FGM Beams: FEM with Innovative Element
M Zakeri A Modarakar Haghighi R AttarnejadThis paper aims at presenting a new efficient element for free vibration and instability analysis of Axially Functionally Graded Materials (FGMs) non-prismatic beams using Finite Element Method (FEM). Using concept of Basic Displacement Functions (BDFs), two- node eleme أکثرThis paper aims at presenting a new efficient element for free vibration and instability analysis of Axially Functionally Graded Materials (FGMs) non-prismatic beams using Finite Element Method (FEM). Using concept of Basic Displacement Functions (BDFs), two- node element extends to three-node element for obtaining much more exact results using FEM. First, BDFs are introduced and computed using energy method such as unit-dummy load method. Afterward, new efficient shape functions are developed in terms of BDFs during the procedure based on the mechanical behavior of the element in which presented shape functions benefit generality and accuracy from stiffness and force method, respectively. Finally, deriving structural matrices of the beam with respect to new shape functions; free vibration and instability analysis of the FGM beam are studied using finite element method for all types of AFGM beams and the convergence of FEM has been studied. The results from both free vibration and instability analysis are in perfect agreement with those of previously published. تفاصيل المقالة -
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82 - Finite Element Instability Analysis of the Steel Joist of Continuous Composite Beams with Flexible Shear Connectors
H Bakhshi H.R RonaghComposite steel/concrete beams may buckle in hogging bending regions. As the top flange of I-beam in that arrangement is restricted from any translational deformation and twist, the web will distort during buckling presenting a phenomenon often described as restricted d أکثرComposite steel/concrete beams may buckle in hogging bending regions. As the top flange of I-beam in that arrangement is restricted from any translational deformation and twist, the web will distort during buckling presenting a phenomenon often described as restricted distortional buckling. There are limited studies available in the literature of restricted distortional buckling of composite steel/concrete I-beams subjected to negative or hogging bending. There is none however that includes the effect of partial shear interaction. In this paper, finite element models for in-plane analysis and out-of-plane buckling of continuous composite I-beams including the effects of partial shear interaction are presented. تفاصيل المقالة -
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83 - Analysis of Laminated Soft Core Sandwich Plate Having Interfacial Imperfections by an Efficient C0 FE Model
R.P Khandelwal A Chakrabarti P BhargavaAn efficient C0 continuous two dimensional (2D) finite element (FE) model is developed based on a refined higher order shear deformation theory (RHSDT) for the static analysis of soft core sandwich plate having imperfections at the layer interfaces. In this (RHSDT) theo أکثرAn efficient C0 continuous two dimensional (2D) finite element (FE) model is developed based on a refined higher order shear deformation theory (RHSDT) for the static analysis of soft core sandwich plate having imperfections at the layer interfaces. In this (RHSDT) theory, the in-plane displacement field for the face sheets and the core is obtained by superposing a globally varying cubic displacement field on a zig-zag linearly varying displacement field. The transverse displacement is assumed to have a quadratic variation within the core and it remains constant in the faces beyond the core. In this theory, the interfacial imperfection is represented by a liner spring-layer model. The proposed model satisfies the condition of transverse shear stress continuity at the layer interfaces and the zero transverse shear stress condition at the top and bottom of the sandwich plate. The nodal field variables are chosen in an efficient manner to circumvent the problem of C1 continuity requirement of the transverse displacements associated with the RHSDT. The proposed model is implemented to analyze the laminated composites and sandwich plates having interfacial imperfection. Many new results are also presented which should be useful for the future research. تفاصيل المقالة -
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84 - A Cohesive Zone Model for Crack Growth Simulation in AISI 304 Steel
F Javidrad M MashayekhyStable ductile crack growth in 3 mm thick AISI 304 stainless steel specimens has been investigated experimentally and numerically. Multi-linear Isotropic Hardening method coupled with the Von-Mises yield criterion was adopted for modeling elasto-plastic behavior of the أکثرStable ductile crack growth in 3 mm thick AISI 304 stainless steel specimens has been investigated experimentally and numerically. Multi-linear Isotropic Hardening method coupled with the Von-Mises yield criterion was adopted for modeling elasto-plastic behavior of the material. Mode-I CT fracture specimens have been tested to generate experimental load-displacement-crack growth data during stable crack growth. The critical fracture energy (JIc) was then determined using the finite elements results in conjunction with the experimental data. The effect of in-plane constraints on the numerical-experimental JIc calculation was then investigated. The results of finite element solution were used to tailor an exponential CZM model for simulation of mode-I stable crack growth in CT specimens. It is found that the adopted CZM is generally insensitive to the applied constraints to the crack tip stress state and thus it can effectively be used for simulating crack growth in this material. تفاصيل المقالة -
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85 - Wave Propagation in Sandwich Panel with Auxetic Core
D Qing-Tian Y Zhi-ChunAuxetic cellular solids in the forms of honeycombs and foams have great potential in a diverse range of applications, including as core material in curved sandwich panel composite components, radome applications, directional pass band filters, adaptive and deployable st أکثرAuxetic cellular solids in the forms of honeycombs and foams have great potential in a diverse range of applications, including as core material in curved sandwich panel composite components, radome applications, directional pass band filters, adaptive and deployable structures, filters and sieves, seat cushion material, energy absorption components, viscoelastic damping materials and fastening devices etc.In this paper, the characteristic of wave propagation in sandwich panel with auxetic core is analyzed. A three-layer sandwich panel is considered which is discretized in the thickness direction by using semi-analytical finite element method. Wave propagation equations are obtained through some algebraic manipulation and applying standard finite element assembling procedures. The mechanical properties of auxetic core can be described by the geometric parameters of the unit cell and mechanical properties of the virgin core material. The characteristics of wave propagation in sandwich panel with conventional hexagonal honeycomb core and re-entrant auxetic core are discussed, and effects of panel thickness, geometric properties of unit cell on dispersive curves are also discussed. Variations of Poisson’s ratio and core density with inclined angle are presented. تفاصيل المقالة -
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86 - The Prediction of Forming Limit Diagram of Low Carbon Steel Sheets Using Adaptive Fuzzy Inference System Identifier
H AleyasinThe paper deals with devising the combination of fuzzy inference systems (FIS) and neural networks called the adaptive network fuzzy inference system (ANFIS) to determine the forming limit diagram (FLD). In this paper, FLDs are determined experimentally for two grades o أکثرThe paper deals with devising the combination of fuzzy inference systems (FIS) and neural networks called the adaptive network fuzzy inference system (ANFIS) to determine the forming limit diagram (FLD). In this paper, FLDs are determined experimentally for two grades of low carbon steel sheets using out-of-plane (dome) formability test. The effect of different parameters such as work hardening exponent (n), anisotropy (r) and thickness on these diagrams were studied. The out-of-plane stretching test with hemispherical punch was simulated by finite element software Abaqus. The limit strains occurred with localized necking were specified by tracing the thickness strain and its first and second derivatives versus time at the thinnest element. In addition, to investigate the effect of different parameters such as work hardening exponent (n), anisotropy (r) and thickness on these diagrams, a machine learning algorithm is used to simulate a predictive framework. The method of learning algorithm uses the rudiments of neural computing through layering the FIS and using hybrid-learning optimization algorithm. In other words, for building the training database of ANFIS, the experimental work and finite element software Abaqus are used to obtain limit strains. Good agreement was achieved between the predicted data and the experimental results. تفاصيل المقالة -
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87 - Mechanical Buckling Analysis of Composite Annular Sector Plate with Bean-Shaped Cut-Out using Three Dimensional Finite Element Method
H Behzad A.R Shaterzadeh M ShariyatIn this paper, mechanical buckling analysis of composite annular sector plates with bean shape cut out is studied. Composite material sector plate made of Glass-Epoxy and Graphite-Epoxy with eight layers with same thickness but different fiber angles for each layer. Mec أکثرIn this paper, mechanical buckling analysis of composite annular sector plates with bean shape cut out is studied. Composite material sector plate made of Glass-Epoxy and Graphite-Epoxy with eight layers with same thickness but different fiber angles for each layer. Mechanical loading to form of uniform pressure loading in radial, environmental and biaxial directions is assumed. The method used in this analysis is three dimensional (3D) finite elements based on the elasticity relations. With zero first and second variation of potential energy of the entire annular sector plate, we find stability equation. Green non-linear displacement strain relations to obtain geometric stiffness matrix is used. Unlike many studies, in present work three dimensional finite elements method has been used with an eight node element and meshing in the thickness direction is done, too. The bean shaped cut out in the sector has increased the complexity of the analysis. The continuing, effect of different parameters including cut out dimensions, fiber angles of layers, loading direction and dimensions of the annular sector plate on the mechanical buckling load has been investigated and interesting results have been obtained. تفاصيل المقالة -
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88 - Spectral Finite Element Method for Free Vibration of Axially Moving Plates Based on First-Order Shear Deformation Theory
M.R Bahrami S HatamiIn this paper, the free vibration analysis of moderately thick rectangular plates axially moving with constant velocity and subjected to uniform in-plane loads is investigated by the spectral finite element method. Two parallel edges of the plate are assumed to be simpl أکثرIn this paper, the free vibration analysis of moderately thick rectangular plates axially moving with constant velocity and subjected to uniform in-plane loads is investigated by the spectral finite element method. Two parallel edges of the plate are assumed to be simply supported and the remaining edges have any arbitrary boundary conditions. Using Hamilton’s principle, three equations of motion for the plate are developed based on first-order shear deformation theory. The equations are transformed from the time domain into the frequency domain by assuming harmonic solutions. Then, the frequency-dependent dynamic shape functions obtained from the exact solution of the governing differential equations is used to develop the spectral stiffness matrix. By solving a non-standard eigenvalue problem, the natural frequencies and the critical speeds of the moving plates are obtained. The exactness and validity of the results are verified by comparing them with the results in previous studies. By the developed method some examples for vibration of stationary and moving moderately thick plates with different boundary conditions are presented. The effects of some parameters such as the axially speed of plate motion, the in-plane forces, aspect ratio and length to thickness ratio on the natural frequencies and the critical speeds of the moving plate are investigated. These results can be used as a benchmark for comparing the accuracy and precision of the other analytical and numerical methods. تفاصيل المقالة -
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89 - An Investigation into Resonant Frequency of Triangular V-Shaped Cantilever Piezoelectric Vibration Energy Harvester
R Hosseini M HamediPower supply is a bottle-neck problem of wireless micro-sensors, especially where the replacement of batteries is impossible or inconvenient. Now piezoelectric material is being used to harvest vibration energy for self-powered sensors. However, the geometry of a piezoe أکثرPower supply is a bottle-neck problem of wireless micro-sensors, especially where the replacement of batteries is impossible or inconvenient. Now piezoelectric material is being used to harvest vibration energy for self-powered sensors. However, the geometry of a piezoelectric cantilever beam will greatly affect its vibration energy harvesting ability. This paper deduces a remarkably precise analytical formula for calculating the fundamental resonant frequency of V-shaped cantilevers using Rayleigh-Ritz method. This analytical formula, which is very convenient for mechanical energy harvester design based on Piezoelectric effect, is then validated by ABAQUS simulation. This formula raises a new perspective that, among all the V-shaped cantilevers and in comparison with rectangular one, the simplest tapered cantilever can lead to maximum resonant frequency and highest sensitivity. تفاصيل المقالة -
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90 - Predicting Depth and Path of Subsurface Crack Propagation at Gear Tooth Flank under Cyclic Contact Loading
H Heirani Kh FarhangdoostIn this paper, a two-dimensional computational model is proposed for predicting the initiation position and propagation path of subsurface crack of spur gear tooth flank. In order to simulate the contact of teeth, an equivalent model of two contacting cylinders is used. أکثرIn this paper, a two-dimensional computational model is proposed for predicting the initiation position and propagation path of subsurface crack of spur gear tooth flank. In order to simulate the contact of teeth, an equivalent model of two contacting cylinders is used. The problem is assumed to be under linear elastic fracture mechanic conditions and finite element method is used for numerical study. An initial subsurface crack is considered in the model at different depths. For each position of the initial crack, moving contact loading is applied to the part and value of ∆KII is obtained for the crack tips. The position of maximum ∆KII is selected as the location of crack initiation. It is shown that the subsurface crack appears at the maximum shear stress point. The maximum tangential stress criterion is used to determine the crack growth angle. The crack is incrementally propagated until the crack tip reaches the part surface and a cavity is formed on the tooth surface. Analyzing the stress field and stress intensity factors are performed in ABAQUS software. The obtained results for the depth and shape of the spall are in good agreement with the experimental results reported in literature. تفاصيل المقالة -
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91 - Analytical and Numerical Modelling of the Axisymmetric Bending of Circular Sandwich Plates with the Nonlinear Elastic Core Material
A Kudin S Choporov Yu Tamurov M.A.V Al OmariHerein paper compares the analytical model with the FEM based numerical model of the axisymmetric bending of circular sandwich plates. Also, the paper describes equations of the circular symmetrical sandwich plates bending with isotropic face sheets and the nonlinear el أکثرHerein paper compares the analytical model with the FEM based numerical model of the axisymmetric bending of circular sandwich plates. Also, the paper describes equations of the circular symmetrical sandwich plates bending with isotropic face sheets and the nonlinear elastic core material. The method of constructing an analytical solution of nonlinear differential equations has been described. The perturbation method for differential equations with small parameters is used to represent nonlinear differential equations as a sequence of linear equations. Linear differential equations are reduced to Bessel’s equation. It is compared results of analytical model with results of other researches using two problems: 1) the problem of axisymmetric transverse bending of a circular sandwich plate, 2) the problem of axisymmetric transverse bending of an annular sandwich plate. The effect of accounting nonlinear elastic core material on the strain state of the sandwich plate is described. تفاصيل المقالة -
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92 - A New Approach to Buckling Analysis of Lattice Composite Structures
S.A Galehdari A.H Hashemian J.E Jam A AtrianBuckling strength of composite latticed cylindrical shells is one of the important parameters for studying the failure of these structures. In this paper, new governing differential equations are derived for latticed cylindrical shells and their critical buckling axial أکثرBuckling strength of composite latticed cylindrical shells is one of the important parameters for studying the failure of these structures. In this paper, new governing differential equations are derived for latticed cylindrical shells and their critical buckling axial loads. The nested structure under compressive axial buckling load was analyzed. Finite Element Method (FEM) was applied to model the structure in order to verify the analytical results. The obtained results were validated based upon the results of previous case studies in literature. For the squared type of lattice composite shells, a new formula for the buckling load was developed and its value was compared to the critical load, using FEM with 3D beam elements. The processes were carried out for three different materials of Carbon/Epoxy, Kevlar/Epoxy and EGlass/Epoxy. تفاصيل المقالة -
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93 - Modal Testing and Finite Element Analysis of Crack Effects on Turbine Blades
K.R.P Babu B.R Kumar K.M RaoThe study of vibration response of a turbine blade helps to detect the crack presence in the blade which alters its dynamic characteristics. The change is characterized by changes in the modal parameters associated with natural frequencies. In this paper, study of vibra أکثرThe study of vibration response of a turbine blade helps to detect the crack presence in the blade which alters its dynamic characteristics. The change is characterized by changes in the modal parameters associated with natural frequencies. In this paper, study of vibration response is made for turbine blade in the presence of a crack like defect. Turbine blade is initially assumed as a cantilever beam. Modal testing has been carried out for both the beams with different crack depth and crack location ratios using FFT spectrum analyzer and ANSYS software. From the analysis, it has been observed that the crack depth and its location have noticeable effect on the natural frequencies. Later the same cantilever beam was twisted with different angle of twists to validate the cantilever beam model to turbine blade. تفاصيل المقالة -
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94 - An Efficient Strain Based Cylindrical Shell Finite Element
M BourezaneThe need for compatibility between degrees of freedom of various elements is a major problem encountered in practice during the modeling of complex structures; the problem is generally solved by an additional rotational degree of freedom [1-3]. This present paper invest أکثرThe need for compatibility between degrees of freedom of various elements is a major problem encountered in practice during the modeling of complex structures; the problem is generally solved by an additional rotational degree of freedom [1-3]. This present paper investigates possible improvements to the performances of strain based cylindrical shell finite element [4] by introducing an additional rotational degree of freedom. The resulting element has 24 degrees of freedom, six essential external degrees of freedom at each of the four nodes and thus, avoiding the difficulties associatedwithinternal degrees of freedom (the three translations and three rotations) and the displacement functions of the developed element satisfy the exact representation of the rigid body motion and constant strains (in so far as this allowed by compatibility equations). Numerical experiments analysis have been conducted to assess accuracy and reliability of the present element, this resulting element with the added degree of freedom is found to be numerically more efficient in practical problems than the corresponding Ashwell element [4]. تفاصيل المقالة -
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95 - Free Vibration of Functionally Graded Cylindrical Shell Panel With and Without a Cutout
k.S Sai Ram K Pratyusha P KiranmayiThe free vibration analysis of the functionally graded cylindrical shell panels with and without cutout is carried out using the finite element method based on a higher-order shear deformation theory. A higher-order theory is used to properly account for transverse shea أکثرThe free vibration analysis of the functionally graded cylindrical shell panels with and without cutout is carried out using the finite element method based on a higher-order shear deformation theory. A higher-order theory is used to properly account for transverse shear deformation. An eight noded degenerated isoparametric shell element with nine degrees of freedom at each node is considered. The stiffness and mass matrices are derived based on the principle of minimum potential energy. The stiffness and mass matrices of the element are evaluated by performing numerical integration using the Gaussian quadrature. The effect of volume fraction exponent on the fundamental natural frequency of simply supported and clamped functionally graded cylindrical shell panel without a cutout is studied for various aspect ratios and arc-length to thickness ratios. Results are presented for variation of the fundamental natural frequency of the cylindrical shell panel with cutout size for simply supported and clamped boundary conditions. تفاصيل المقالة -
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96 - Ductile Failure and Safety Optimization of Gas Pipeline
P Zamani A Jaamialahmadi M ShariatiSafety and failure in gas pipelines are very important in gas and petroleum industry. For this reason, it is important to study the effect of different parameters in order to reach the maximum safety in design and application. In this paper, a three dimensional finite e أکثرSafety and failure in gas pipelines are very important in gas and petroleum industry. For this reason, it is important to study the effect of different parameters in order to reach the maximum safety in design and application. In this paper, a three dimensional finite element analysis is carried out to study the effect of crack length, crack depth, crack position, internal pressure and pipe thickness on failure mode and safety of API X65 gas pipe. Four levels are considered for each parameter and finite element simulations are carried out by using design of experiments (DOE). Then, multi-objective Taguchi method is conducted in order to minimize x and y coordinates of Failure Assessment Diagram (FAD). So, desired levels that minimize the coordinates and rises the possibility of safety are derived for each parameter. The variation in FAD coordinates according to the changes in each parameter are also found. Finally, comparisons between the optimum design and all other experiments and simulations have shown a good safety situation. It is also concluded that the more design parameters close to optimum levels, the better safety condition will occur in FAD. A verification study is performed on the safety of longitudinal semi-elliptical crack and the results has shown a good agreement between numerical and experimental results. تفاصيل المقالة -
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97 - Three-Dimensional Finite Element Analysis of Stress Intensity Factors in a Spherical Pressure Vessel with Functionally Graded Coating
H EskandariThis research pertains to the three-dimensional (3D) finite element analysis (FEA) of the stress intensity factors (SIFs) along the crack front in a spherical pressure vessel coated with functionally graded material (FGM). The vessel is subjected to internal pressure an أکثرThis research pertains to the three-dimensional (3D) finite element analysis (FEA) of the stress intensity factors (SIFs) along the crack front in a spherical pressure vessel coated with functionally graded material (FGM). The vessel is subjected to internal pressure and thermal gradient. The exponential function is adopted for property of FGMs. SIFs are obtained for a wide variety of crack shapes and layer thickness. The reported results clearly show that the material gradation of coating and the crack configuration can significantly affect the variation of SIFs along the crack front. The results are given which are applicable for fatigue life assessment and fracture endurance of FGM coating spherical pressure vessel and can be used in design purposes. تفاصيل المقالة -
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98 - Analyzing Frequency of Conical (∆ shaped) Tanks
F SaljughiA finite element analysis is presented for sloshing and impulsive motion of liquid-filled conical tanks during lateral anti-symmetric excitation. The performed analyses led to the development of a number of charts which can be used to identify the natural frequency, the أکثرA finite element analysis is presented for sloshing and impulsive motion of liquid-filled conical tanks during lateral anti-symmetric excitation. The performed analyses led to the development of a number of charts which can be used to identify the natural frequency, the mode shapes of conical tanks for both fundamental and the cos(θ)-modes of vibration. Conical tank geometry was described with several parameters namely, bottom radius( Rb) total height of liquid (h), angle of inclination of the tanks(θi), as variables. Numerical result of the free vibration was obtained for the cases of conical tanks with θi=0 and compared with existing experiments and other predicated results, showing a good agreement between the experiment and numerical results. تفاصيل المقالة -
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99 - Dynamic Simulation and Mechanical Properties of Microtubules
M Motamedi M Mosavi MashhadiThis work is conducted to obtain mechanical properties of microtubule. For this aim, interaction energy in alpha-beta, beta-alpha, alpha-alpha, and beta-beta dimers was calculated using the molecular dynamic simulation. Force-distance diagrams for these dimers were obta أکثرThis work is conducted to obtain mechanical properties of microtubule. For this aim, interaction energy in alpha-beta, beta-alpha, alpha-alpha, and beta-beta dimers was calculated using the molecular dynamic simulation. Force-distance diagrams for these dimers were obtained using the relation between potential energy and force. Afterwards, instead of each tubulin, one sphere with 55 KDa weight connecting to another tubulin with a nonlinear connection such as nonlinear spring could be considered. The mechanical model of microtubule was used to calculate Young’s modulus based on finite element method. Obtained Young’s modulus has good agreement with previous works. Also, natural frequency of microtubules was calculated based on finite element method. تفاصيل المقالة -
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100 - Free and Forced Transverse Vibration Analysis of Moderately Thick Orthotropic Plates Using Spectral Finite Element Method
M.R Bahrami S HatamiIn the present study, a spectral finite element method is developed for free and forced transverse vibration of Levy-type moderately thick rectangular orthotropic plates based on first-order shear deformation theory. Levy solution assumption was used to convert the two- أکثرIn the present study, a spectral finite element method is developed for free and forced transverse vibration of Levy-type moderately thick rectangular orthotropic plates based on first-order shear deformation theory. Levy solution assumption was used to convert the two-dimensional problem into a one-dimensional problem. In the first step, the governing out-of-plane differential equations are transformed from time domain into frequency domain by discrete Fourier transform theory. Then, the spectral stiffness matrix is formulated, using frequency-dependent dynamic shape functions which are obtained from the exact solution of the governing differential equations. An efficient numerical algorithm, using drawing method is used to extract the natural frequencies. The frequency domain dynamic responses are obtained from solution of the spectral element equation. Also, the time domain dynamic responses are derived by using inverse discrete Fourier transform algorithm. The accuracy and excellent performance of the spectral finite element method is then compared with the results obtained from closed form solution methods in previous studies. Finally, comprehensive results for out-of-plane natural frequencies and transverse displacement of the moderately thick rectangular plates with six different combinations of boundary conditions are presented. These results can serve as a benchmark to compare the accuracy and precision of the numerical methods used. تفاصيل المقالة -
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101 - Extended Finite Element Method for Statics and Vibration Analyses on Cracked Bars and Beams
F Mottaghian A Darvizeh A AlijaniIn this paper, the extended finite element method (XFEM) is employed to investigate the statics and vibration problems of cracked isotropic bars and beams. Three kinds of elements namely the standard, the blended and the enriched elements are utilized to discretize the أکثرIn this paper, the extended finite element method (XFEM) is employed to investigate the statics and vibration problems of cracked isotropic bars and beams. Three kinds of elements namely the standard, the blended and the enriched elements are utilized to discretize the structure and model cracks. Two techniques referred as the increase of the number of Gauss integration points and the rectangle sub-grid are applied to refine the integration within the blended and enriched elements of the beam in which the priority of the developed rectangle sub-grid technique is identified. The stiffness and the mass matrices of the beam are extended by considering the Heaviside and the crack tip functions. In a plane stress analysis, the effects of various crack positions and depths, different boundary conditions and other geometric parameters on the displacement and the stress contours are detected. Moreover, in a free vibration analysis, changes of the natural frequencies and the mode shapes due to the aforementioned effects are determined. تفاصيل المقالة -
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102 - Finite Element Modeling of the Vibrational Behavior of Single-Walled Silicon Carbide Nanotube/Polymer Nanocomposites
S Rouhi R Ansari A NikkarThe multi-scale finite element method is used to study the vibrational characteristics of polymer matrix reinforced by single-walled silicon carbide nanotubes. For this purpose, the nanoscale finite element method is employed to simulate the nanotubes at the nanoscale. أکثرThe multi-scale finite element method is used to study the vibrational characteristics of polymer matrix reinforced by single-walled silicon carbide nanotubes. For this purpose, the nanoscale finite element method is employed to simulate the nanotubes at the nanoscale. While, the polymer is considered as a continuum at the larger scale. The polymer nanotube interphase is simulated by spring elements. The natural frequencies of nanocomposites with different nanotube volume percentages are computed. Besides, the influences of nanotube geometrical parameters on the vibrational characteristics of the nanocomposites are evaluated. It is shown that reinforcing polymer matrix by single-walled silicon carbide nanotubes leads to increasing the natural frequency compared to neat resin. Increasing the length of the nanotubes at the same diameter results in increasing the difference between the frequencies of nanocomposite and pure polymer. Besides, it is observed that clamped-free nanocomposites experience a larger increase in the presence of the nanotubes than clamped-clamped nanotube reinforced polymers. تفاصيل المقالة -
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103 - Investigation of Stability in earth dam using Ansys, and Geo –Studio Software
علی دلوری نژاد هوشنگ حسونی زاده امیرعباس کمان بدستAnalysis of seepage and stability is considered as an important case in designing which today, withadvanced numeric software acceptable results will be obtained before and after Construction. In thepresent study, the behavior of earth dam against effective factors was i أکثرAnalysis of seepage and stability is considered as an important case in designing which today, withadvanced numeric software acceptable results will be obtained before and after Construction. In thepresent study, the behavior of earth dam against effective factors was investigated by softwareAnsys12. The studied dam is Maroun soil dam, which is located in 19Km north of Behbehan andconstructed on Maroun River. This dam is soil- gravely dam. It was tried in this research that stabilityof dam be evaluated by finite element method and Ansys software, and then compare by softwareresults like Geo-studio. At first Following, the stability of dam slope was considered and the behaviorof dam was stimulated by several methods and there were relatively same results for the amount ofsafety factor and unstable surface. Safety factor was 4.21 for upstream by bishop method in Ansys and4.71 in Geo-studio and for downstream 1.5, 1.8, respectively. Finally, the maximum and minimumamount of tension was determined by analyzing tension, strain and movement and the areas withdifferent sediments and possible cracking and subside regions were determined. In this part, bothsoftwares provided relatively same results and the maximum amount of movement in dam estimated5-6 meters. However, both softwares are best ones in analyzing and finite method and completelycorrect introducing of current conditions could have acceptable analyses. تفاصيل المقالة -
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104 - Break fill-dam simulation using GeoStudio (case study: Safarood earth dam, Kerman)
حسن زمانپور مهدی فولادی پناهOne of the main reason of earth-dam breaks is inner erosion which is caused by washing fine soil particles and finally lead to seepage inside the dam. Seepage will decrease effective tension in the earth-dam's core and arching phenomena is occurred. More settlement of c أکثرOne of the main reason of earth-dam breaks is inner erosion which is caused by washing fine soil particles and finally lead to seepage inside the dam. Seepage will decrease effective tension in the earth-dam's core and arching phenomena is occurred. More settlement of core than to shell is the consequence of arching and occurrence of cracking. In this paper, GeoStudio software based on finite element scheme was used to simulate numerical modeling of Safarood earth-dam according to two scenarios: (a) after construction; (b) after the first water impounding. Doing calibration and verification processes in SEEP/W and SIGMA/W modules, nonlinear elastic behavior and Mohr-Coulomb's elastic-plastic behavior was determined for core and body of the dam during calibration and verification processes with correlation coefficient of 0.94 and 0.921 between measured and calculated data. In this research, vertical tension distribution, horizontal and vertical displacement, and total tension were calculated and analyzed. After the first water impounding at ratio y/h less than 0.1, hydraulic failure is probable in Safarood earth-dam. تفاصيل المقالة -
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105 - تحلیل المان محدود دندان آسیای کوچک دو ریشه فک بالا به کمک پست و کور ریخته‌گری شده و تاثیر وجود فرول
محمد شیشه ساز رضا امیری مقدم اسدالله احمدزادههدف از انجام این تحقیق، بررسی توزیع تنش در مجموعه‌ی پست و کور، در دندان آسیای کوچک فک بالا با دو ریشه است. در چنین دندانی، پست و کور به صورت یک‌پارچه و دو تکه منظور شده‌اند. برای تهیه‌ی مدل پایه‌ی دندان، از دندان کشیده‌شده‌ی یک بیمار ارتودنسی استفاده گردید. سپس به منظور أکثرهدف از انجام این تحقیق، بررسی توزیع تنش در مجموعه‌ی پست و کور، در دندان آسیای کوچک فک بالا با دو ریشه است. در چنین دندانی، پست و کور به صورت یک‌پارچه و دو تکه منظور شده‌اند. برای تهیه‌ی مدل پایه‌ی دندان، از دندان کشیده‌شده‌ی یک بیمار ارتودنسی استفاده گردید. سپس به منظور تهیه‌ی مدل سه بعدی رایانه‌ای، به کمک دستگاه اسکنر سه‌بعدی، مدل پایه‌ی دندان تهیه گردید. پس از آن در نرم‌افزارهای مدلسازی مهندسی سالیدورک، مدل رایانه‌ای تکمیل و سپس برای تحلیل تنش در تحلیل‌گر انسیس، تحت دو بار محوری و مورب 45 درجه با اندازه‌ی 400 نیوتن قرار گرفت. جنس انتخاب شده برای پست و کور در هردو حالت یک‌پارچه و دوتکه، آلیاژ نیکل-کروم منظور شد. نتایج نشان می-دهند که استفاده از فرول در تمامی حالات، باعث کاهش تنش در ریشه‌ها می‌شود؛ همچنین مشاهده گردید که استفاده از فرول، لزوماً باعث کاهش تنش در پست و کور نمی‌گردد. بیشینه تنش معادل فون-مایزز در ریشه‌ها، مستقل از بار وارده، در حالت پست و کور دوتکه کمتر از حالت پست و کور یک‌پارچه بود. علاوه بر آن، مشخص شد که تحت بار مورب، تنش بیشتری در اجزای مجموعه‌ی پست و کور ایجاد می‌شود. تفاصيل المقالة -
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106 - تحلیل و شبیه سازی توزیع دما بر پیکره غلتک در طی فرآیند نورد گرم
امیرحشمت خدمتی بازکیائی علی سوزنگرصنعت نورد، متداولترین و پر رونق ترین روش تولید فرآورده های فلزی است. نخستین هدف فرآیند نورد، کاهش سطح مقطع و یا ضخامت قطعه کار است، این عمل به دو صورت نورد گرم و سرد انجام می پذیرد، فلز از بین دو غلتک عبور نموده تا شکل شیار ( کالیبر ) غلتک را بگیرد، بدین جهت غلتک‌های نو أکثرصنعت نورد، متداولترین و پر رونق ترین روش تولید فرآورده های فلزی است. نخستین هدف فرآیند نورد، کاهش سطح مقطع و یا ضخامت قطعه کار است، این عمل به دو صورت نورد گرم و سرد انجام می پذیرد، فلز از بین دو غلتک عبور نموده تا شکل شیار ( کالیبر ) غلتک را بگیرد، بدین جهت غلتک‌های نورد اجزاء مهمی در کارخانجات نوردی می‌باشند. هدف از انجام این پژوهش تحلیل انتقال حرارت در شرایط کارکرد نورد گرم و یافتن توزیع حرارت در غلتک‌های نورد با استفاده از شبیه سازی اجزاء محدود میباشد، شبیه سازی به صورت غیر خطی بوده و فرض گردیده که غلتک همگن، همسانگرد، بدون ترک و کرنش حرارتی و دمای محیط برابر دمای اتاق در نظر گرفته شده است. توزیع حرارت در غلتک در این پژوهش به دو صورت با استفاده از سیستم خنک‌کاری پاششی و بدون استفاده از این سیستم بدست آمده و پس از آن نتایج بدست آمده از شبیه سازی اجزاء محدود را با داده‌های آزمایشگاهی استخراج شده، مورد صحت سنجی قرار گرفته شده است که بالاترین میزان درصد خطای نسبی در پیشبینی 08/334 درصد بوده که بیانگر تطبیق نتاایج حاصله از حل عددی با داده استخراجی بوده است. تفاصيل المقالة -
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107 - اثر گالری روغن بر تنش‌های ترمومکانیکی پیستون
حجت عاشوری افشین افشاریپیستون قلب یک موتور است که تحت بارگذاری حرارتی و مکانیکی قرار داشته و با توجه به اینکه نوسانات شدید دما و فشار گاز را تحمل می‌کند، قطعه‌ای بسیار بحرانی محسوب می‌شود. هدف این پژوهش ارزیابی اثر گالری روغن بر تنش‌های ترمومکانیکی پیستون موتور XU7JP/L3 است. برای این منظور اب أکثرپیستون قلب یک موتور است که تحت بارگذاری حرارتی و مکانیکی قرار داشته و با توجه به اینکه نوسانات شدید دما و فشار گاز را تحمل می‌کند، قطعه‌ای بسیار بحرانی محسوب می‌شود. هدف این پژوهش ارزیابی اثر گالری روغن بر تنش‌های ترمومکانیکی پیستون موتور XU7JP/L3 است. برای این منظور ابتدا از نرم‌افزار سالیدورکس جهت مدلسازی پیستون موتور استفاده گردید. گالری روغن در قسمت سر پیستون نیز طراحی گردید. سپس از نرم‌افزار انسیس جهت تحلیل تنش‌های ترمومکانیکی پیستون استفاده شد. درنهایت اثر گالری روغن بر توزیع تنش‌های ترمومکانیکی پیستون مورد مطالعه و ارزیابی قرار گرفت. شرایط مرزی در تحلیل حرارتی و مکانیکی از شبیه‌سازی یک بعدی در نرم‌افزارهای جی‌تی پاور و متلب استخراج گردید. نتایج تحلیل حرارتی نشان داد که گالری روغن باعث کاهش دمای پیستون موتور درحدود 12 درجه سانتیگراد می‌شود. نتایج تحلیل مکانیکی نشان داد که تنش وان مایسس در پیستون اصلاح شده درحدود 13 مگاپاسکال کاهش می‌یابد. برای بررسی صحت نتایج تحلیل ترمومکانیکی، نتایج شبیه‌سازی شده با نمونه واقعی پیستون آسیب دیده مقایسه گردید و نشان داده شد که نواحی بحرانی، مطابقت مناسبی با نواحی گسیختگی در نمونه واقعی دارد. تفاصيل المقالة -
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108 - شبیه سازی تنش های حرارتی در فرآیند نورد گرم و تاثیر آن ها بر شکست غلتک
امیرحشمت خدمتی بازکیائی علی سوزنگرفرایند نورد، در واقع شکل دهی فولاد می باشد که در آن از غلتک هایی برای ایجاد تغییر شکل، بهبود خواص مکانیکی مواد و از بین بردن یکنواختی فلز استفاده می گردد. فولاد را می توان در دو فرم گرم و سرد نورد نمود، که هر یک از آنها ویژگی های خاص خود را دارند. هدف از انجام این پژوه أکثرفرایند نورد، در واقع شکل دهی فولاد می باشد که در آن از غلتک هایی برای ایجاد تغییر شکل، بهبود خواص مکانیکی مواد و از بین بردن یکنواختی فلز استفاده می گردد. فولاد را می توان در دو فرم گرم و سرد نورد نمود، که هر یک از آنها ویژگی های خاص خود را دارند. هدف از انجام این پژوهش بررسی تاثیر تنش‌های حرارتی حاصله در حین فرآیند نورد بر شکست غلتک‌ها با استفاده از شبیه سازی اجزاء محدود بوده است. این شبیه سازی به صورت غیر خطی بوده و فرض گرديده كه غلتك همگن، همسانگرد، بدون ترك و كرنش حرارتي و دماي محيط برابر دمای اتاق در نظر گرفته شده است. در این پژوهش تاثیر خنک‌کاری اصولی و دقیق در حین فرآیند نورد نیز مورد بررسی قرار گرفته است. نتایج بدست آمده در شش پاس نورد گرم با توجه به بیشترین دمای غلتک‌ها و میزان تنش فون‌مایزز ایجاده شده در غلتک‌ها نشان داده شده و میزان نقش تنش‌های حرارتی بر شکست غلتک‌ها بیان شده است. تفاصيل المقالة -
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109 - تحلیل خستگی چندمحوره منیفولد دود با درنظر گرفتن تنش ویسکوزیته
حجت عاشوریمنیفولد دود به علت هندسه پیچیده و شرایط بارگذاری يکی از چالش برانگیزترين قطعات موتور است. این قطعه باید نوسانات سیکلی تنش های ترمومکانیکی را در طول عمر خود تحمل کند. بنابراین شبیه سازی و تحلیل ترک های خستگی آن لازم و ضروری است. در این پژوهش، تحلیل عمر خستگی کم چرخه منیف أکثرمنیفولد دود به علت هندسه پیچیده و شرایط بارگذاری يکی از چالش برانگیزترين قطعات موتور است. این قطعه باید نوسانات سیکلی تنش های ترمومکانیکی را در طول عمر خود تحمل کند. بنابراین شبیه سازی و تحلیل ترک های خستگی آن لازم و ضروری است. در این پژوهش، تحلیل عمر خستگی کم چرخه منیفولد دود با استفاده از روش اجزای محدود و نرم افزار آباکوس به منظور پیش بینی دما و تنش و سپس عمر خستگی با استفاده از معیار چندمحوره صفحه بحرانی براون-میلر و نرم افزار MSC-FATIGUE انجام شده است. از ترکیب الگوی سخت شوندگی غیرخطی همگن-سینماتیک چابوچه با قانون تنش ویسکوز به منظور درنظر گرفتن اثر تنش ویسکوزیته استفاده شده است. نتایج تحلیل ترمومکانیکی نشان داد که بیشینه دما و تنش وان-مایسز 7/757 درجه سانتی¬گراد و 2/395 مگاپاسکال است و موقعیت آن در ناحیه همریختگاه است. پس همریختگاه منیفولد دود موتور ناحیه بحرانی است و احتمال ایجاد ترک های خستگی در آن وجود دارد. عمر خستگی منیفولد دود بدون و با در نظرگرفتن اثر تنش ویسکوزیته به ترتیب 9310 و 8850 سیکل محاسبه گردید. به عبارت دیگر درنظر نگرفتن اثر تنش ویسکوزیته در تحلیل عمر خستگی باعث می شود که تعداد سیکل های گسیختگی 460 سیکل یا حدود 2/5 درصد بیشتر از میزان مجاز تخمین زده شود. بنابراین لازم است اثر تنش ویسکوزیته در تحلیل عمر خستگی منیفولد دود درنظر گرفته شود. براي بررسي صحت نتايج تحلیل ترمومکانیکی و عمر خستگی، نتايج شبيه سازي شده با نمونه واقعي منیولد دود آسيب ديده مقايسه گردید و نشان داده شد که نواحي بحراني، مطابقت مناسبی با نواحي گسیختگی در نمونه واقعي دارد. تفاصيل المقالة -
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110 - مدلسازی عددی ضرایب ظرفیت باربری خاک زیر پی تحت بار زلزله
پژمان فاضلی سهیل قرهارزیابی ضرایب ظرفیت باربری خاک زیر پی، تحت بار زلزله از گذشته تا به حال همواره مورد توجه محققین مختلف بوده اسـت. در تمـامیمطالعات و تحلیل های انجام شده، بار زلزله به صورت های مختلفی با عملکرد شبه استاتیک در نظر گرفته شده و موجب بدست آمدن نتایجمتفاوتی شده است. در این تحق أکثرارزیابی ضرایب ظرفیت باربری خاک زیر پی، تحت بار زلزله از گذشته تا به حال همواره مورد توجه محققین مختلف بوده اسـت. در تمـامیمطالعات و تحلیل های انجام شده، بار زلزله به صورت های مختلفی با عملکرد شبه استاتیک در نظر گرفته شده و موجب بدست آمدن نتایجمتفاوتی شده است. در این تحقیق، ارزیابی ضرایب ظرفیت باربری خاک تحت بار زلزله، به کمک نرم افزار اجـزاء محـدود PLAXISانجـامشده و نتایج بدست آمده با نتایج ارائه شده توسط سایر محققین مورد ارزیابی و مقایسه قرار گرفته است. به علاوه تأثیر اینرسی توده خاک زیرپی بر ضرایب ظرفیت باربری خاک در حالت شبه استاتیک مدل سازی عددی گردید، نتایج حاکی از آن است کـه ضـرایب ظرفیـت بـاربریبدست آمده از بار شبه استاتیک در مدل سازی عددی تقریبی خوب و مناسب از نتایج ارائه شده توسط سایر محققین می باشد. از سویی دیگربا در نظر گرفتن اثر اینرسی توده خاک زیر پی، نتایج ارزیابی ضرایب ظرفیت باربری ناشی از بار شبه استاتیک در مدل سازی عددی نسبت بهنتایج به دست آمده از سایر محققین محافظه کارانه تر بوده و در تمامی موارد در جهت اطمینان می باشد. در نهایت با توجه به این که بار شبهاستاتیک به عنوان یک معیار کاملاً ایدهآل جایگزین مناسبی برای تأثیر بار زلزله نمی باشد، اثر توده خاک زیر پی بر چگـونگی و نحـوه انتقـالامواج زلزله تا رسیدن به بستر پی نیز، مورد ارزیابی قرار گرفته است تفاصيل المقالة -
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111 - بررسی تاثیر تغییرات GSIسقف بلاواسطه بر طول گام تخریب دوره ای معادن زغال سنگ با استفاده از روش عددی
اصغر نوروزی کاظم اورعی مهرداد جوادی کامران گشتاسبیروش استخراج جبهه کار طولانی یکی از پرکاربرد ترین روش ها در استخراج معادن زغال سنگ است. از مهمترین پارامترهایی که در ایمنیو موفقیت عملیات استخراجی به روش جبهه کارطولانی موثر می باشد، تخمین طول گام تخریب دوره ای است. چرا که در نظر گرفتنطولی کمتر از مقدار واقعی، می تواند ب أکثرروش استخراج جبهه کار طولانی یکی از پرکاربرد ترین روش ها در استخراج معادن زغال سنگ است. از مهمترین پارامترهایی که در ایمنیو موفقیت عملیات استخراجی به روش جبهه کارطولانی موثر می باشد، تخمین طول گام تخریب دوره ای است. چرا که در نظر گرفتنطولی کمتر از مقدار واقعی، می تواند با انتخاب سیستم نگهداری ناکافی، جان معدنکاران را به خطر اندازد و همچنین در نظر گرفتنطولی بیشتر از مقدار واقعی، هزینه های اضافی را به معدن تحمیل نماید. از طرفی وجود ناپیوستگی های موجود در سقف بلاواسطهتاثیرات منفی در طول گام تخریب معادن زغال سنگ دارد. در این تحقیق براساس مدلسازی های عددی متعدد با مقادیر متفاوت GSIطول گام تخریب برای هر حالت از GSIمحاسبه گردیده و معادله طول گام تخریب بر اساس تغییرات GSIتعیین گردیده است. بهمنظور ارزیابی نتایج مدل ارائه گردیده، نتایج حاصل از بررسی طول گام تخریب دوره ای در یازده پانل از معادن هندوستان با نتایج مدلمذکور، مورد ارزیابی قرار گرفته است. با بررسی انجام شده، ملاحظه گردید که نتایج حاصل از مدل ارائه گردیده و نتایج مقادیر عملی گامتخریب دوره ای معادن هندوستان، به خوبی با هم منطبق می باشند تفاصيل المقالة -
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112 - بررسی پتانسیل وقوع همگرایی و انفجار سنگ و مقایسه آن با روش عددی المان محدود
عارف جابری فواد زمانیارزیابیخطرات زمین شناسی درموردحفریاتزیرزمینیوازآنجملهتونل هادرشرایطمچالهشونده و انفجار سنگ،ازجملهپارامترهایموثردر طراحیاینسازه هااست. احداث سامانه تونل انتقال آب از سد آزاد به دشت دهگلان –قروه به منظور آبرسانی به دشت های دهگلان- قروه می باشد. با توجه به جنس ضعیف ت أکثرارزیابیخطرات زمین شناسی درموردحفریاتزیرزمینیوازآنجملهتونل هادرشرایطمچالهشونده و انفجار سنگ،ازجملهپارامترهایموثردر طراحیاینسازه هااست. احداث سامانه تونل انتقال آب از سد آزاد به دشت دهگلان –قروه به منظور آبرسانی به دشت های دهگلان- قروه می باشد. با توجه به جنس ضعیف تا خیلی ضعیفتوده سنگ مسیر تونل و ضخامت روباره و به دلیل قرار گیری مسیر تونل در زون فعال از لحاظ تکتونیکی امکان وقوع پدیده مچاله شوندگی و انفجار سنگ وجود داشت. در این پژوهش ابتدا با استفاده از برداشت های زمین شناسی و مغزه های حاصل از حفاری گمانه ها، تونل به 5 زون تقسیم بندی شد. در ادامه به بررسی مچاله شوندگی و انفجار سنگ برای هر 5 زون پرداخته شد که براساس این بررسی ها و با توجه به روش تجربی و نیمه تجربی تونل به ترتیب در محدوده بدون مچاله شوندگی و مچاله شوندگی شدید قرار گرفت، همچنین مسیر تونل از لحاظ انفجار سنگ پتانسیلی کمی داشت. در نهایت به منظور تحلیل جابجایی رخ داده در تونل اقدام به مقایسه بین روش هوک و مارینوس و روش کرنش بحرانی با روش عددی المان محدود با نرم افزار phase 2 شد. براساس تحلیل های صورت گرفته مشخص شد که روش کرنش بحرانی بیشترین تطابق را با روش عددی داشت. باتوجهبهتطابق مناسبنتایجعددیبانتایج روشکرنش بحرانیمی توان زون S3 و S5رابهعنوانناپایدارترینزونهامعرفی کرد. تفاصيل المقالة -
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113 - کاربرد روش سطح پاسخ درتحلیل جذب انرژی لوله های مخروطی جدار نازک شیار دار پر شده از فوم پلی اورتان
بتول سرکبیری علی جهان محمد جواد رضوانیچکیده جاذب های انرژی در صنایع مختلف به ویژه در صنایع خودرو سازی به عنوان راه حلی برای کاهش اثر ضربه وارده به سرنشینان و بالا بردن ایمنی خودرو بکار می روند. لوله‌های جدار نازک به عنوان یکی از کارآمدترین سیستمهای جذب انرژی امروزه کاربرد روزافزونی پیدا کرده‌اند. دراین تحقی أکثرچکیده جاذب های انرژی در صنایع مختلف به ویژه در صنایع خودرو سازی به عنوان راه حلی برای کاهش اثر ضربه وارده به سرنشینان و بالا بردن ایمنی خودرو بکار می روند. لوله‌های جدار نازک به عنوان یکی از کارآمدترین سیستمهای جذب انرژی امروزه کاربرد روزافزونی پیدا کرده‌اند. دراین تحقیق، جذب انرژی با بررسی تاثیرات متغیر های طراحی مربوط به لوله های جدار نازک مخروط شیار دار با استفاده از آنالیز المان محدود انجام می شود.اما از آنجائیکه که خروجی اینگونه مطالعات بیشتر به نحوه طراحی آزمایشات محاسباتی وابسته است در این مطالعه از تکنیک طراحی آزمایشات همراه با آنالیز المان محدود استفاده شده است. بدین منظور لوله آلومنیومی مخروطی شکل پر شده از فوم پلی اورتان که شیارها در سطوح داخل و خارج آن و با فواصل مساوی ایجاد شده اند ، تحت بار شبه استاتیک شبیه سازی میگردد.هدف طراحی شامل جذب انرژی ویژه و متغیرهای طراحی شامل زاویه مخروط ،فاصله شیارها،چگالی فوم ،عمق شیار و ضخامت لوله است. روش سطح پاسخ نشان می دهد که ضخامت لوله ، چگالی فوم ،عمق شیار و فاصله بین شیارها به ترتیب ذکر شده و بصورت خطی با میزان جذب انرژی ارتباط دارند. این نتایج میتواند در طراحی لوله های جدار نازک مخروطی با هندسه متفاوت مفید باشد. تفاصيل المقالة -
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114 - بررسی نحوه پخش تنش و مکانیزم شکست در روسازیهای انعطاف پذیر با استفاده از روش المان محدود
علی بابائیاین مقاله به صورت تئوری مکانیزم های احتمالی توزیع تنش در لایه‌های روسازی قیری را با استفاده از روش المان محدود بررسی می‌کند و همچنین تاثیر یکنواخت فشار عمودی و افقی و توزیع تنش اصلی بین تایر و لایه‌های روسازی را مورد آزمایش قرار می دهد. یک روسازی مدل شده از قسمتهای: 1- أکثراین مقاله به صورت تئوری مکانیزم های احتمالی توزیع تنش در لایه‌های روسازی قیری را با استفاده از روش المان محدود بررسی می‌کند و همچنین تاثیر یکنواخت فشار عمودی و افقی و توزیع تنش اصلی بین تایر و لایه‌های روسازی را مورد آزمایش قرار می دهد. یک روسازی مدل شده از قسمتهای: 1- قشر راه 2- لایه اساس 3- لایه زیر اساس دانه‌ای 4- بستر راه تشکیل شده است. چگونگی عملکرد بار به اینصورت است که یک جفت چرخ با فشار استاندارد انتخاب می‌شود. نتایج نشان می‌دهد که تنش‌های فشاری و کشش بین چرخ‌ها به حد قابل توجهی می‌رسد احتمالا خستگی در جایی آغاز می‌شود که بیشترین تنش از بالا تا پایین لایه‌ها رخ می‌دهد. اگر چه تنش عمودی در تمام لایه‌های روسازی تاثیر‌گذار است تنش افقی فقط در قشر راه و لایه اساس موثر است. تفاصيل المقالة -
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115 - شبیه سازی یک فرایند هیدروفرمینگ ورقه ای برای قطعات فنجانی شکل تیتانیمی و اعتبارسنجی
فریبرز فروهندههیدروفرمینگ ورقهای در بین روشهای شکل‌دهی به‌دلیل برتری‌هایی مانند بهتربودن کیفیت سطح محصول، نسبت کشش بیشتر، نیاز کمتر به عملیات دوباره مانند ماشین‌کاری متداول گردیده است. تیتانیم و آلیاژهای آن نه تنها به دلیل نسبت استحکام به وزن بالا بلکه به دلیل توانایی کار در دماهای أکثرهیدروفرمینگ ورقهای در بین روشهای شکل‌دهی به‌دلیل برتری‌هایی مانند بهتربودن کیفیت سطح محصول، نسبت کشش بیشتر، نیاز کمتر به عملیات دوباره مانند ماشین‌کاری متداول گردیده است. تیتانیم و آلیاژهای آن نه تنها به دلیل نسبت استحکام به وزن بالا بلکه به دلیل توانایی کار در دماهای بالا بسیار پرکاربرد می باشد. در این مقاله فرایند هیدروفرمینگ ورقهای به روش المان محدود شبیه‌سازی شده است. پارامترهای مختلف مانند نیروی ورق‌گیر، نرخ کرنش، فشار سیال، توزیع ضخامت و غیره مورد تحلیل قرار گرفته است. یک دستگاه هیدروفرمینگ ورقهای بر مبنای نتایج حاصل از شبیه‌سازی طراحی و ساخته شده است. دستگاه با انواع فلزات و آلیاژها به‌خصوص فلز تیتانیم مورد آزمایش قرار گرفته است. اعتبار مناسبی از مقایسه نتایج شبیه‌سازی و آزمایشگاهی به‌دست آمده است. در نهایت خصوصیات مواد محصولات هیدروفرم شده ارائه شده و برتری روش مذکور نسبت به روشهای سنتی به اثبات رسیده است. تفاصيل المقالة -
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116 - بررسی عددی و تجربی پارامترهای تعداد دور سیم‌پیچ و ولتاژ در شکل‌دهی الکترومغناطیس صفحات آلومینیوم آلیاژ 1050
سجاد نادیان برسیانی احمد کشاورزی امین کلاهدوزبا پیشرفت علم دانشمندان روشهای جدید را جایگزین روشهای قدیمی میکنند. امروزه خودرو سازان جهت کاهش وزن خودرو‌ها از ورق‌هایی با ضخامت پایین استفاده میکنند که جهت شکل‌دهی آنها نیاز به روشهای جدیدی میباشد. شکل‌دهی الکترومغناطیس یک روش شکل‌دهی میباشد که بوسیله آن می‌توا أکثربا پیشرفت علم دانشمندان روشهای جدید را جایگزین روشهای قدیمی میکنند. امروزه خودرو سازان جهت کاهش وزن خودرو‌ها از ورق‌هایی با ضخامت پایین استفاده میکنند که جهت شکل‌دهی آنها نیاز به روشهای جدیدی میباشد. شکل‌دهی الکترومغناطیس یک روش شکل‌دهی میباشد که بوسیله آن میتوان قطعات بسیار نازک را شکل‌دهی نمود. در شکل دهی الکترومغناطیس با تخلیه انرژی الکتریکی در سیم‌پیچ‌های آن میدان مغناطیسی به وجود می‌آید که همانند سنبه ولی بدون اثر گذاری قطعه-کار را به سمت قالب هدایت می‌کند و باعث شکل‌دهی آن می‌شود. این عمل در مدت زمان کمتر از یک میکروثانیه انجام می‌شود و باعث می‌شود تعداد قطعات تولید شده از این روش افزایش یابند. با توجه به اینکه سیم‌پیچ‌ها رابط بین دستگاه و قطعه‌کار می‌باشند، در این پژوهش به بررسی عددی و تجربی تعداد دور سیم‌پیچ و ولتاژ در شکل‌دهی الکترومغناطیس پرداخته می‌شود. جهت انجام آزمایش‌های عملی سیم‌پیچ‌های الکترومغناطیس ساخته شده و با استفاده از دستگاه الکترومغناطیس با قدرت 3 کیلوژول آزمایش‌ها انجام می‌شوند. جهت انجام آزمایش‌های عددی نیز از نرم‌افزار آباکوس و جی‌مگ استفاده شده است که نتایج عددی با نتایج تجربی مطابقت خوبی داشته است. پس از انجام آزمایش‌ها، مشاهده شد که سیم‌پیچ‌ها باید هم مساحت با قطعه‌کار در نظر گرفته شوند و جهت شکل‌دهی مساحت‌های بزرگی از ورق باید شکل‌دهی در چند مرحله با سیم‌پیچ‌های کوچک انجام شود. همچنین جهت افزایش استحکام سیم‌پیچ‌ها در زمان شکل‌دهی باید سیم‌پیچ‌ها در محلول‌های اف کا 20 قرار گیرند. تفاصيل المقالة -
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117 - بررسی عددی و بهینه سازی پارامترهای قالب فرایند فشار در کانال های زاویه دار موازی
امین آرمانیان حسن خادمی زادهامروزه مواد فوق ریز دانه به دلیل خواص کم نظیر خود جایگاه ویژه ای در صنایع مختلف پیدا کرده اند. با کاهش اندازه دانه، سهم اتم‌های موجود در مرز دانه‌ها افزایش‌یافته و زیادشدن مرز دانه ها موجب جلوگیری از حرکت نابه جایی ها و بالا رفتن استحکام می-شود. یکی از روش های تولید موا أکثرامروزه مواد فوق ریز دانه به دلیل خواص کم نظیر خود جایگاه ویژه ای در صنایع مختلف پیدا کرده اند. با کاهش اندازه دانه، سهم اتم‌های موجود در مرز دانه‌ها افزایش‌یافته و زیادشدن مرز دانه ها موجب جلوگیری از حرکت نابه جایی ها و بالا رفتن استحکام می-شود. یکی از روش های تولید مواد فوق ریز دانه، اعمال تغییر شکل پلاستیک شدید می باشد. جهت اعمال تغییر شکل پلاستیک می-توان از روش های بسیاری استفاده نمود که در این پژوهش از کانال های زاویه دار موازی استفاده می شود. جهت بررسی عددی این فرایند از نرم افزار المان محدود آباکوس و جهت بهینه سازی نتایج از روش شبکه عصبی و الگوریتم ژنتیک استفاده شده است. در این پژوهش اثر پارامتر های قالب که شامل زاویه کانال، طول لوله، افزایش اختلاف قطر و ضریب اصطکاک می باشد، بررسی می شود. نتایج نشان داد که ضریب اصطکاک و طول لوله مورد آزمایش هر کدام جداگانه بر همگن شدن توزیع کرنش بسیار نقش داشته است، به طوری که با افزایش مقدار ضریب اصطکاک تعریفی و کاهش میزان طول لوله، توزیع کرنش به سمت همگنی و یکنواختی سوق پیدا خواهد کرد. تفاضل افزایش قطر لوله و زاویه کانال قالب تاثیر چندانی بر بهبود یکنواختی توزیع کرنش نخواهند داشت. از سوی دیگر افزایش ضریب اصطکاک، طول لوله و افزایش قطر لوله هر کدام جداگانه منجر به افزایش نیروی فرایند می شوند درحالی که افزایش زاویه کانال قالب منجر به کاهش نیروی شکل دهی شد. تفاصيل المقالة -
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118 - تحلیل ارتعاشی پوسته جعبه دنده ماشین سنگین با استفاده از روش اجزا محدود
حسام تراب زاده کاشی محسن مردانیدر این این مقاله بررسی تاثیر خواص مواد مختلف بر روی فرکانسهای طبیعی و شکل مود ارتعاشی پوسته دیفرانسیل نوعی ماشین سنگین مورد بررسی قرار گرفته است. خواص مکانیکی مواد مختلف نقش بسزایی در تعیین فرکانسهای خروجی و تغییر شکلهای ارتعاشی در یک سیستم ایفا میکنند. به این منظور در أکثردر این این مقاله بررسی تاثیر خواص مواد مختلف بر روی فرکانسهای طبیعی و شکل مود ارتعاشی پوسته دیفرانسیل نوعی ماشین سنگین مورد بررسی قرار گرفته است. خواص مکانیکی مواد مختلف نقش بسزایی در تعیین فرکانسهای خروجی و تغییر شکلهای ارتعاشی در یک سیستم ایفا میکنند. به این منظور در نرم افزار طراحی CATIA مدل دیفرانسیل ایجاد و به نرم افزار شبیه ساز ABAQUS وارد شده است که قابلیت بالایی در تخمین رفتار دینامیکی سیستمهای مختلف دارد. موادی نظیر چدن خاکستری با قابلیت جذب ارتعاش بالا، فولاد با چگالی و صلبیت زیاد و آلیاژهای آلومینیوم و منیزیم با چگالی پایین برای پوسته دیفرانسیل مورد بررسی قرار گرفته‌اند. نتایج بررسی نشان داد که محدوده فرکانس طبیعی پنج مود اول ارتعاشی در این مواد با یکدیگر متفاوت و انتخاب چدن خاکستری میتواند ضمن کاهش ارتعاش از ایجاد پدیده تشدید جلوگیری نماید. بخش دیگری از شبیه‌سازی عددی به بررسی تاثیر نوع اتصال بین دو قسمت دیفرانسیل بر روی رفتار دینامیکی اختصاص یافته است. به این منظور یکی از پیچ‌های اتصال دو قسمت دیفرانسیل به صورت محکم نشده در نرم افزار وارد شد، عیبی که ممکن است در هنگام تعمیرات توسط اپراتور ایجاد شود. نتایج شبیه‌سازی عددی حاکی از اینست که با محکم نکردن تنها یکی از پیچ‌های اتصال، فرکانسهای طبیعی حدود 3 تا 4 درصد کاهش می‌یابد که این امر میتواند احتمال ایجاد پدیده تشدید را افزایش دهد. تفاصيل المقالة -
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119 - بررسی اثر هندسه پلیسه رو بر جریان مواد و شکل گیری عیوب در فورجینگ سرد آلیاژ آلومینیوم 3003
میلاد بنداد کرمانی مهرداد عضو امینیانهدف از این پژوهش بررسی تاثیر هندسه پلیسه‌رو بر روی جریان داخلی مواد، پیش بینی عیوب و پارامترهای فرایند فورجینگ سرد است. به همین منظور سه شکل هندسی پلیسه رو های ذوزنقه ای، بیضوی و مربعی بر روی یک قطعه ساده مخروطی شکل مورد بررسی قرار گرفت. تاثیر هندسی پلیسه رو ها با استفا أکثرهدف از این پژوهش بررسی تاثیر هندسه پلیسه‌رو بر روی جریان داخلی مواد، پیش بینی عیوب و پارامترهای فرایند فورجینگ سرد است. به همین منظور سه شکل هندسی پلیسه رو های ذوزنقه ای، بیضوی و مربعی بر روی یک قطعه ساده مخروطی شکل مورد بررسی قرار گرفت. تاثیر هندسی پلیسه رو ها با استفاده از نرم افزار المان محدود آباکوس شبیه‌سازی شد و پس از آن قالب با پلیسه رو بهینه، ساخته شد و فرایند فورجینگ جهت راستی آزمایی نتایج شبیه سازی بر روی یک قطعه از جنس آلیاژ آلومینیوم 3003، انجام گرفت. نتایج حاصل نشان داد، شکل پلیسه رو ذوزنقه ای نسبت به دیگر موارد، شرایط مناسبتری برای جریان مواد ایجاد می‌کند. براساس نتایج شبیه سازی، بیشینه مقدار کرنش پلاستیک در اطراف پلیسه رو اتفاق افتاد و مقدار آن در قالب با پلیسه رو ذوزنقه ای نسبت به قالب های بیضوی و مربعی بیشتر بود که ناشی از سیلان بیشتر مواد در پلیسه رو ذوزنقه ای بود. توزیع و اعمال فشار مورد نیاز جهت تولید قطعه نهایی بر روی قطعه کار با پلیسه رو مربعی شکل بیشتر از نمونه های دیگر در شبیه سازی پیش بینی شد. بیشینه فشار اعمال شده توسط قالب بر روی قطعه کار در قسمت پلیسه رو بود که برای پلیسه رو مربعی شکل، بیشترین مقدار خود را داشت و در مورد پلیسه رو ذوزنقه ای کمترین مقدار را دارا بود. تفاصيل المقالة -
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120 - شبیه سازی تاثیر دما و زمان بر میزان برگشت فنری در فرآیند خمکاری لوله
محمدحسین تهرانی مهرداد عضو امینیانفرآیند خمکاری یکی از پرکاربردترین فرآیندها در شکل دهی فلزات می باشد. با توجه به محدود بودن ضریب الاستیسیته مواد ، در پی تغییر شکل پلاستیکی،پس از برداشتن بار همواره یک بازیابی الاستیک وجود دارد. در فرآیند خمکاری لوله، کاهش میزان برگشت فنری و بهینه سازی فرآیند دارای اهمیت أکثرفرآیند خمکاری یکی از پرکاربردترین فرآیندها در شکل دهی فلزات می باشد. با توجه به محدود بودن ضریب الاستیسیته مواد ، در پی تغییر شکل پلاستیکی،پس از برداشتن بار همواره یک بازیابی الاستیک وجود دارد. در فرآیند خمکاری لوله، کاهش میزان برگشت فنری و بهینه سازی فرآیند دارای اهمیت است. در این مقاله اثر پارامترهای دما و زمان بر میزان برگشت فنری برروی خمکاری لوله های زنگ نزن فولادی و آلومینیومی بررسی شده است. برای این منظور به کمک روش المان محدود و با استفاده از نرم افزار شبیه سازی آباکوس فرآیند خمکاری شبیه سازی شده است ، این شبیه سازی برای حالت های مختلف دما و زمان مورد بررسی قرار گرفته است. در نهایت برای صحه گذاری نتایج شبیه سازی یک سری آزمایشات تجربی برای خمکاری این لوله ها انجام شده است. نتایج بدست آمده از هر دو روش مطابقت خوبی باهم دارند. بطوریکه که با افزایش دما میزان برگشت فنری کاهش می یابد و همچنین با گذشت زمان از انجام فرآیند خمکاری، میزان درصد برگشت فنری کاهش می یابد. تفاصيل المقالة -
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121 - طراحی و مدلسازی آزمون فراصوت آرایه فازی و شبیه سازی انتشار دسته پرتو امواج فراصوتی در ورق فلزی به کمک نرم افزار اجزای محدود آباکوس
شهرام یاره ییاز روش های نوین آزمون و ارزیابی های غیرمخـرب فراصـوتی، استفـاده از پروب هـایی با چند المان تحریـک پذیر جهت انتشار امواج در ماده می باشـد. پروب آرایه فازی خطی، نوعی از پروب های آرایه فازی است که چینش المان ها در آن به طور ردیفی در امتداد یک خط می باشد. در این پژوهش، ضمن أکثراز روش های نوین آزمون و ارزیابی های غیرمخـرب فراصـوتی، استفـاده از پروب هـایی با چند المان تحریـک پذیر جهت انتشار امواج در ماده می باشـد. پروب آرایه فازی خطی، نوعی از پروب های آرایه فازی است که چینش المان ها در آن به طور ردیفی در امتداد یک خط می باشد. در این پژوهش، ضمن معرفی آزمون های غیرمخرب فراصوت آرایه فازی، با ارائه ی ملاحضات حل معادله موج به کمک اجزا محدود و با استفاده از نرم افزار آباکوس، آزمون فراصوت آرایه فازی با یک پروب 8 المانی خطی مدلسازی می شود. انتشار دسته پرتو امواج فراصوتی در نمونه به دو صورت مستقیم و مورب شبیه سازی خواهد شد که اساس پایش مستقیم و قطاعی هستند. از مهمترین نکاتی که باید در شبیه سازی انتشار دسته پرتو امواج فراصوت با المان های متعدد لحاظ شود، اعمال تاخیر زمانی تحریک هر المان با توجه به جهت انتشار موج می باشد. در این مقاله به نحوه ی محاسبه ی تاخیرهای زمانی اشاره می شود. جهت راستی آزمایی نتایج آباکوس، بخشی به عنوان صحت سنجی در این مقاله ارائه می شود. استفاده از روش اجزا محدود و نتایج آن علاوه بر بهبود درک مفاهیم آزمون فراصوت آرایه فازی، طراحی آزمون با فرض شرایط مختلف که در نتیجه ی آزمون تاثیر گـذار می باشند، با صرف حداقل هزینه و زمان ممکن می شود. تفاصيل المقالة -
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122 - تشخیص انکیلوز بودن دندان با استفاده از فرکانس طبیعی
زاوش امینی احسان جمشیدی فائزه اسلامی پورچکیده در این مقاله فرکانسهای دندان در حالت طبیعی و انکیلوز(فک جوش) بررسی و مقایسه میگردد. در درمان ارتودنسی اصل درمان بر مبنای جابجایی و چرخش دندانها است عدم تشخیص انکیلوز بودن دندان درمان ارتودنسی را طولانی و کم اثر می‌نماید حال آنکه در عکسهای سی تی اسکن تشخیص انکیلو أکثرچکیده در این مقاله فرکانسهای دندان در حالت طبیعی و انکیلوز(فک جوش) بررسی و مقایسه میگردد. در درمان ارتودنسی اصل درمان بر مبنای جابجایی و چرخش دندانها است عدم تشخیص انکیلوز بودن دندان درمان ارتودنسی را طولانی و کم اثر می‌نماید حال آنکه در عکسهای سی تی اسکن تشخیص انکیلوز بودن دندان با دشواری صورت می-گیرد. در این پژوهش ابتدا عکسهای بدست آمده از سی تی اسکن توسط نرم‌افزار میمیکس به مدل سه بعدی تبدیل گردید سپس در نرم‌افزار ماجیک نقاط اضافی موجود در مدل حذف گردیده و مدل برای تحلیل آماده میگردد مدل دندان به نرم‌افزار سالیدورک انتقال یافته و برای آن لیگامان و فک متناظر با آن ساخته شد سپس مدل به نرم‌افزار آباکوس که از روش المان محدود برای تحلیل استفاده می‌کند وارد گردید، چگالی و مدول یانگ برای هریک از قسمتهای دندان، فک و لیگامان تعریف شد همچنین برهم کنش بین اعضاء مشخص گردید برای فک و دندان بتنهایی فرکانس طبیعی بدست آمد که از فرکانس مجموعه فک، دندان و لیگامنت بالاتر میباشد برای مجموعه فک، دندان و لیگامان در حالت عادی و انکیلوز فرکانس طبیعی بدست آمد که فرکانس طبیعی در حالت انکیلوز بسیار بالاتر از فرکانس طبیعی در حالت عادی میباشد و از این روش میتوان برای تشخیص انکیلوز بودن دندان استفاده نمود. تفاصيل المقالة -
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123 - مطالعه‌ی تجربی و عددی اثرموج انفجار حاصل از ماده منفجره بر روی ورقهای آلومینیومی
شهرام یاره یی مجید گنجیانفجار یک واکنش شیمیایی سریع در ماده است، که ماده‌ای اولیه را به گاز تبدیل می کند. فرآیند انفجار به دو بخش کلی شروع انفجار و فرآیند برهم‌کنش میان محصولات گازی و محیط اطراف تقسیم می شود. شناخت رفتار الاستیک-پلاستیک و پیش بینی فشار پارگی صفحات دایروی مورد استفاده در لوله أکثرانفجار یک واکنش شیمیایی سریع در ماده است، که ماده‌ای اولیه را به گاز تبدیل می کند. فرآیند انفجار به دو بخش کلی شروع انفجار و فرآیند برهم‌کنش میان محصولات گازی و محیط اطراف تقسیم می شود. شناخت رفتار الاستیک-پلاستیک و پیش بینی فشار پارگی صفحات دایروی مورد استفاده در لوله شاک ها و ارتباط آن با پارامترهای هندسی ورق های دایروی لازم است. بنابراین از لوله شاک در تحلیل و ایجاد موج شاک و شبیه سازی بار انفجاری روی صفحات استفاده می شود. در این مقاله با استفاده از آزمایشات تجربی و مدلسازی المان محدود، به بررسی اثر موج انفجار ناشی از ماده منفجره بر روی ورق های آلومینیومی پرداخته می شود. برای شبیه سازی آزمایش ها از نرم افزار هیدروکد اتوداین انسیس استفاده خواهد شد. همچنین به منظور انجام آزمایش تجربی، لوله شاکی با ابعاد مشخص برای بررسی اثر انفجار مواد منفجره بر روی ورق های هدف طراحی و ساخته شد. تفاصيل المقالة -
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124 - بررسی تاثیر جهت گیری هسته لانه زنبوری نسبت به صحفات جانبی بر قابلیت جذب انرژی پنل ساندویچی استفاده شده در چاله آسانسور
امیر قیاسوند حسین احمدی رشید سوان حسنی فردپنل های ساندویچی دارای قابلیت و توان بالا در زمینه جذب انرژی و مستهلک سازی انرژی جنبشی حاصل از برخورد در مواجهه با موج های انفجاری می باشند. در پژوهش حاضر تاثیر جهت گیری هسته لانه زنبوری پنل ساندویچی نسبت به صفحات جانبی و راستای بارگذاری بر قابلیت جذب و مستهلک سازی انرژ أکثرپنل های ساندویچی دارای قابلیت و توان بالا در زمینه جذب انرژی و مستهلک سازی انرژی جنبشی حاصل از برخورد در مواجهه با موج های انفجاری می باشند. در پژوهش حاضر تاثیر جهت گیری هسته لانه زنبوری پنل ساندویچی نسبت به صفحات جانبی و راستای بارگذاری بر قابلیت جذب و مستهلک سازی انرژی ناشی از برخورد کابین آسانسور با پنل ساندویچی تعبیه شده در چاله آسانسور مورد بررسی قرار گرفته است. از شش زاویه 30, 20, 10, 5, 0 و 45 درجه بدین منظور استفاده گردید. مشاهده شد که با افزایش میزان زاویه جهت گیری هسته پنل نسبت به راستای ضربه میزان سختی پنل دچار افت خواهد شد و این افت با افزایش بیشتر زاویه جهت گیری هسته به صورت شدید تری اتفاق خواهد افتاد. با افزایش میزان زاویه هسته لانه زنبوری از حد بهینه، سازه به دلیل کرنش پلاستیک بزرگ فشردگی و مچالگی را تجربه خواهد نمود که این امر موجب افزایش شدید سختی پنل می گردد و پنل به دلیل عدم تراکم پذیری همانند یک جسم صلب عمل می نماید و قابلیت مستهلک سازی انرژی آن به شدت دچار کاهش می گردد. تفاصيل المقالة -
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125 - بررسی تاثیر شکل و عیوب صفحات لانهزنبوری در قابلیت جذب انرژی به روش المان محدود
رامین مشک آبادی بنیامین طهماسپوردر تحقیق حاضر با شبیه‌سازی المان محدود سازه لانهزنبوری و با استفاده از تحلیل‌های شبه استاتیکی، به بررسی تأثیر پارامترهایی مانند ابعاد هندسی عیوب و هندسه‌های مختلف سلولی بر روی میزان جذب انرژی سازه پرداخته شده است. در انجام تحلیل‌ها درصد عیوب مختلف شامل 0، 10 و 20 درصد أکثردر تحقیق حاضر با شبیه‌سازی المان محدود سازه لانهزنبوری و با استفاده از تحلیل‌های شبه استاتیکی، به بررسی تأثیر پارامترهایی مانند ابعاد هندسی عیوب و هندسه‌های مختلف سلولی بر روی میزان جذب انرژی سازه پرداخته شده است. در انجام تحلیل‌ها درصد عیوب مختلف شامل 0، 10 و 20 درصد عیب مورد مطالعه قرار گرفته است. نتایج تحقیق نشان میدهند که در پنل لانهزنبوری با هندسه سلولی نوع A، ساختار به صورت کامل تخریب می‌شود که این امر میتواند در نتیجه عدم تقارن سلول‌های سازه باشد. در دو مدل دیگر، سازه شکل کلی خود را حفظ کرده و با تغییر شکل منظم ایجاد شده در سلول‌ها، این نوع هندسه‌ها توانایی بیشتری در قابلیت جذب انرژی حین برخورد را دارا هستند. همچنین، نتایج نشان میدهند وجود عیب در ساختار پنل‌ها تأثیر قابل ملاحظه‌ای بر قابلیت جذب انرژی در این سازه‌ها دارد و با افزایش میزان عیوب قابلیت جذب انرژی نیز کاهش می‌یابد. بررسی نتایج نشان می‌دهد که تأثیر عیوب بر میزان کاهش قابلیت جذب انرژی سازه‌های لانهزنبوری با ساختار سلول از نوع A، به مراتب بسیار بیشتر از دو نوع دیگر میباشد. تفاصيل المقالة -
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126 - توسعه مدل آیروالاستیسیته پره کامپوزیتی و تحلیل اثر چرخش و افزایش طول بر فرکانسهای طبیعی
رضا اثباتی لواسانی شاهرخ شمسدر این پژوهش معادلات آیروالاستیسیته خطی پره توربین بادی با روش گسسته سازی المان محدود جهت درنظر گرفتن اثر چرخش و افزایش طول بر فرکانسهای طبیعی استخراج شده است. پره یک تیر یکسر گیردار اویلر-برنولی کامپوزیتی در نظر گرفته شده و با روش المان محدود مدل شده است. با بکارگیری أکثردر این پژوهش معادلات آیروالاستیسیته خطی پره توربین بادی با روش گسسته سازی المان محدود جهت درنظر گرفتن اثر چرخش و افزایش طول بر فرکانسهای طبیعی استخراج شده است. پره یک تیر یکسر گیردار اویلر-برنولی کامپوزیتی در نظر گرفته شده و با روش المان محدود مدل شده است. با بکارگیری روش همیلتونین معادلات حرکت را بدست آمده است. ماتریس‌های المان محدود با تعیین جابجایی گره‌ها و فرض رابطه خطی در جابجایی محوری و تابع هرمیشن در جهات عرضی و پیچشی محاسبه می‌شوند. اعتبار سنجی معادلات به صورت عددی بر روی پره با شبیه سازی سیستم معادلات و بررسی فرکانسهای طبیعی و شکل مدها انجام شده است. همچنین اثر افزایش طول پره و چرخش پره در پره کوتاه و بلند کامپوزیتی بررسی شده است. بررسی فرکانسهای طبیعی نشان می‌دهد فرکانسهای اول و دوم پره‌های بلند تحت تاثیر افزایش طول و چرخش هستند. اما در فرکانسهای بالا و همچنین در پره کوتاه اثر افزایش طول و چرخش کمتر از یک درصد است. تفاصيل المقالة -
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127 - بررسی ارتعاشات و دمپینگ صفحات کامپوزیتی ساندویچی تقویت شده با الیاف کولار
عبدالحسین فریدون علی حضرتی نیاریهدف از این مقاله بررسی دمپینگ ارتعاشی صفحات کامپوزیت ساندویچی تقویت شده با استفاده از روش ریتز میباشد. میباشد. دمپینگ یک پارامتر موثر در کنترل میزان ارتعاشات سازه های متحرک میباشد. به دلیل چقرمگی و استحکام بالای مواد کامپوزیتی به نسبت وزن آنها، این مواد در حوزه های مختل أکثرهدف از این مقاله بررسی دمپینگ ارتعاشی صفحات کامپوزیت ساندویچی تقویت شده با استفاده از روش ریتز میباشد. میباشد. دمپینگ یک پارامتر موثر در کنترل میزان ارتعاشات سازه های متحرک میباشد. به دلیل چقرمگی و استحکام بالای مواد کامپوزیتی به نسبت وزن آنها، این مواد در حوزه های مختلفی از جمله صنایع اتومبیل سازی و مهندسی مکانیک مورد استفاده قرار میگیرند. محاسبات تئوری با استفاده از نرم افزار مطلب ورژن 8-7 انجام شده است. در ادامه، دمپینگ با استفاده از نرم افزار تجاری آباکوس (ورژن 5-6) مورد ارزیابی قرار گرفته است. نتایج بدست آمده از روش تئوری با نتایج بدست آمده از روش المان محدود مطابقت خوبی از خود نشان میدهند. تفاصيل المقالة -
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128 - تاثیر عیوب ریخته گری بر پارامترهای مودال بلوک سیلندر خودرو
امیر حسین عموزاده مرتضی محمدظاهری احسان جمشیدیدر این مقاله،به تاثیر عیوب ریخته گری بر فرکانس طبیعی بلوک سیلندر خودرو توجه شده است . لذا برای این منظور بلوک سیلندر خودرو توسط نرم افزارSalid work،مدل سه بعدی شده است و سپس با نرم افزار المان محدود Ansys Workbench مدل المان محدود رسم شده و فرکانس طبیعی بلوک سیلندر در م أکثردر این مقاله،به تاثیر عیوب ریخته گری بر فرکانس طبیعی بلوک سیلندر خودرو توجه شده است . لذا برای این منظور بلوک سیلندر خودرو توسط نرم افزارSalid work،مدل سه بعدی شده است و سپس با نرم افزار المان محدود Ansys Workbench مدل المان محدود رسم شده و فرکانس طبیعی بلوک سیلندر در مدل FEM بدست آمده است. با استفاده از آزمایش مودال، فرکانس طبیعی بلوک سیلندر گرفته شده است. با تایید شدن مدل FEM توسط نتایج آزمایش مودال،شبیه سازی عیوب در مدل FEM به صورت تک به تک صورت گرفته و فرکانس طبیعی بلوک سیلندر برای تک تک عیوب به دست آمده است.با محاسبه اختلاف فرکانس طبیعی مدل سالم با مدل معیوب،تاثیر تک تک عیوب بر فرکانس طبیعی قطعه به طور قابل ملاحظه ای مشاهده شده است. تفاصيل المقالة -
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129 - مدلیزاسیون رفتار مکانیکی یک میراگر مگنتورئولوژیکال دوار
ایمان باقرزاده علی معظمی گودرزیتحلیل و بررسی رفتار مکانیکی یک نمونه میراگر مگنتورئولوژیکال دوار بهینه سازی شده موضوع این مقاله می باشد. میراگر مورد مطالعه تشکیل شده است از یک دیسک دوار که درون یک محفظه استوانه ای بسته، پرشده با سیال مگنتورئولوژیکال، قرار می گیرد و حول محور خود با سرعتی ثابت می چرخد. أکثرتحلیل و بررسی رفتار مکانیکی یک نمونه میراگر مگنتورئولوژیکال دوار بهینه سازی شده موضوع این مقاله می باشد. میراگر مورد مطالعه تشکیل شده است از یک دیسک دوار که درون یک محفظه استوانه ای بسته، پرشده با سیال مگنتورئولوژیکال، قرار می گیرد و حول محور خود با سرعتی ثابت می چرخد. با تغییر جریان الکتریکی گذرنده از سیم پیچی که به دور استوانه پیچیده شده است، میدان مغناطیسی درون استوانه ایجاد می شود که به تغییر ویسکوزیته اسمی در سیال مگنتورئولوژیکال می انجامد و با تغییر آن، گشتاور مقاوم سیال در برابر دوران دیسک تغییر می کند. بر این اساس می توان با تغییر شدت جریان الکتریکی ضریب میرایی را مدیریت نمود. در راستای اهداف این مقاله، پس از تعیین مقادیر بهینه برای پارامتر های هندسی میراگر مانند شعاع و ضخامت دیسک فرومغناطیس با توجه به محدودیت های ابعاد هندسی که در طراحی اولیه لحاظ شده، اثر شدت جریان الکتریکی بر رفتار مکانیکی میراگر مورد بررسی قرار می گیرد. تفاصيل المقالة -
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130 - عیب یابی سر سیلندر خودرو با استفاده از امواج مکانیکی و هوش مصنوعی
مجتبی دوست محمدی مرتضی محمدظاهری احسان جمشیدیایمنی قطعات و ماشین آلات برای کاربران آن ها امری مهم تلقی می شود و عیوب قطعات به عنوان یکی از مهم ترین عوامل تهدید کننده سلامتی قطعات همواره مورد توجه بوده است. در این مقاله روشی نو جهت استفاده از شبکه عصبی مصنوعی بر پایه عیب یابی سرسیلندر خودرو پراید به کمک امواج مکانی أکثرایمنی قطعات و ماشین آلات برای کاربران آن ها امری مهم تلقی می شود و عیوب قطعات به عنوان یکی از مهم ترین عوامل تهدید کننده سلامتی قطعات همواره مورد توجه بوده است. در این مقاله روشی نو جهت استفاده از شبکه عصبی مصنوعی بر پایه عیب یابی سرسیلندر خودرو پراید به کمک امواج مکانیکی ارائه شده است. در ابتدا سرسیلندر خودرو با جزئیات کامل مدلسازی شده است و سپس در نرم افزار اجزاء محدود مدل اجزاء محدود بدست آورده شده است. سپس برای تایید و اعتبار سنجی به مدل اجزاء محدود، قطعه تحت تست مودال قرار گرفته و بعد از تایید مدل شبیه سازی عیب ها بر روی مدل اجزاء محدود انجام شده است. با شبیه سازی اعمال نیرو بر مدل (FEM) سیگنال شتاب – زمان دو مدل سالم و معیوب برای هر عیب محاسبه می شود. و با استفاده از امضای مکانیکی عیوب (اختلاف شتاب بین دو مدل سالم و معیوب) و آموزش آن به یک شبکه عصبی مصنوعی پرسپترون چند لایه (MLP) که اختلاف سیگنال شتاب را به موقیعت عیب ارتباط می دهد. عیب یابی سرسیلندر خودرو (تخمین مکانی عیب) صورت گرفته است. نتایج بدست آمده قابلیت شبکه عصبی طراحی شده در تخمین موقیعت عیب را به خوبی نشان می دهد تفاصيل المقالة -
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131 - اصلاح مدل اجزاء محدود به روش تابع پاسخ (RFM)
محمدرضا آشوری حمید دائیان احسان جمشیدیامروزه بدلیل پیچیده شدن طراحی ها، بررسی رفتار سازه های دینامیکی بکمک اجزاء محدود بسیار مورد توجه قرار گرفته است و با ظهور کامپیوتر های قدرتمند استفاده از این روش ها توسط طراحان با شتاب بیشتری صورت می گیرد. روش دیگر دستیابی به یک مدل دینامیکی برای سازه های مکانیکی، ساختن أکثرامروزه بدلیل پیچیده شدن طراحی ها، بررسی رفتار سازه های دینامیکی بکمک اجزاء محدود بسیار مورد توجه قرار گرفته است و با ظهور کامپیوتر های قدرتمند استفاده از این روش ها توسط طراحان با شتاب بیشتری صورت می گیرد. روش دیگر دستیابی به یک مدل دینامیکی برای سازه های مکانیکی، ساختن مدل آزمایشگاهی برای سازه با انجام تستهای ارتعاشی و تحلیل داده های اندازه گیری شده می باشد. به این فرایند در اصطلاح تست مودال (Modal Testing) می گویند که در طی سه دهه گذشته در تئوری و عمل توسعه بسیاری یافته است. یکی از مهمترین کاربردهای تست مودال، بهبود مدلهای عددی سیستم های دینامیکی با مقایسه پارامترهای مودال حاصل از نتایج تست مودال و مدلهای عددی می باشد. پس از بهبود مدل عددی، می توان با اطمینان از آن در تحلیل های بعدی مانند پیش بینی پاسخ به یک نیروی وارده بر سازه، کوپلینگ سازه ها، تحلیل تنش و غیره استفاده کرد. در این مقاله مزایا، معایب و محدودیتهای یکی از روشهای امروزی بهبود مدل دینامیکی سازه ها بنام روش تابع پاسخ (Response Function Method) مورد بررسی قرار گرفته است. همچنین برای درک بهتر روش یک مدل 5 درجه آزادی جرم و فنر توسط نرم افزار MATLAB مدل گردیده است. تفاصيل المقالة -
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132 - Design and optimization of dc brushless permanent magnet motor
Hassan hatamlu Zahra hatamlu ramin borjali navesiElectric motors that have found wide application in various sectors of industry Have unique features such as high reliability, high efficiency, quick acceleration and have small sizes. Brushless DC motors meet these requirements well. In this study, the design of a brus أکثرElectric motors that have found wide application in various sectors of industry Have unique features such as high reliability, high efficiency, quick acceleration and have small sizes. Brushless DC motors meet these requirements well. In this study, the design of a brushless DC motor speed limits for the particular application at 1800 rpm that can be equivalent to 140 watts output was provided.Aims to increase the power density, efficiency and reduce engine weight by using the finite element method. according to the analysis of the existing motors and parameter extraction, comparing them with software for high electromagnetic torque and low weight , in this article we have focused on the permanent magnet by testing with different types of magnets and comparing the results of finite element analysis. The existing magnets made of ceramics with the lowest density , but the permanent magnet in software method has the highest energy density. تفاصيل المقالة -
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133 - New Design of Mems piezoresistive pressure sensor
Hamsa Kamali Asghar charminThe electromechanical analysis of a piezoresistive pressure microsensor with a square-shaped diaphragm for low-pressure biomedical applications is presented. This analysis is developed through a novel model and a finite element method (FEM) model. A microsensor with a d أکثرThe electromechanical analysis of a piezoresistive pressure microsensor with a square-shaped diaphragm for low-pressure biomedical applications is presented. This analysis is developed through a novel model and a finite element method (FEM) model. A microsensor with a diaphragm 1000 „m length and with thickness=400 µm is studied. The electric response of this microsensor is obtained with applying voltage into senseor in p-type piezoresistors located on the diaphragm surface. The diaphragm that is 10 „m thickexhibits a maximum deflection of 3.74 „m using the designed model, which has a relative difference of 5.14 and 0.92% with respect to the comsol model, respectively. The maximum sensitivity and normal stress calculated using the this model are 1.64 mV/V/kPa and 102.1 MPa, respectively. The results of the polynomial model agree well with the Timoshenko model and FEM model for small deflections. In addition, the designed model can be easily used to predict the deflection, normal stress, electric response and sensitivity of a piezoresistive pressure microsensor with a square-shaped diaphragm under small deflections. تفاصيل المقالة -
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134 - Design and simulation of a fast SAW waveguide with Comsol software
Hadi Amos Majid GhandchiIn this paper, the structure of SAW has been studied. In previous work in SAW, materials such as lithium niobium, lithium tantalite and gallium nitride were used in the structure of SAW, and thus had a low operating frequency and the highest reported operating frequency أکثرIn this paper, the structure of SAW has been studied. In previous work in SAW, materials such as lithium niobium, lithium tantalite and gallium nitride were used in the structure of SAW, and thus had a low operating frequency and the highest reported operating frequency was about 4 GHz. In this paper, aluminum nitride and gallium nitride in the SAW structure are used in combination. The electrodes used in the structure are also made of aluminum. Comsol software was used to simulate the structure, and for the structure, the operating frequency was 7.02 GHz.and this wave guide by this design have a better performance of another structures تفاصيل المقالة -
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135 - Modeling of Iranian crust deformation in 2007 using satellite geodetic observations
Tohid malekzadeh DilmaghaniIn this study, using the data of Iran's permanent geodynamic network in two six-month APECs in 2007, a two-dimensional model of surface deformation of the Earth's crust in Iran will be presented. For this purpose, two methods of numerical solution, one finite element an أکثرIn this study, using the data of Iran's permanent geodynamic network in two six-month APECs in 2007, a two-dimensional model of surface deformation of the Earth's crust in Iran will be presented. For this purpose, two methods of numerical solution, one finite element and the other method of relative distance changes, have been used to calculate the strain tensor. In the finite element method, the results obtained depend on the shape of the element. Of course, this issue should be studied in practice and the results should be compared. This method gives the same answer to the hypothesis that the deformation is homogeneous in the desired element only for homogeneous networks with any type of elementation. The resulting strain for the center of gravity of all the elements was the same size and in the same direction, indicating the homogeneity of the deformation in the lattice. تفاصيل المقالة -
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136 - Reliability Analysis of a Mounted Moldboard Plow Bottom Standard using the FORM Method
Seyed Mohammad Reza Nazemosadat Mojtaba Naderi-Boldaji Davoud Ghanbarian Mohammad Amin NematollahiABSTRACT Using the reliability index to express a system’s safety, reliability theory is applied to study a structure’s failure probability due to the uncertainty (i.e., randomness) of design and production parameters with (a) variability in working conditio أکثرABSTRACT Using the reliability index to express a system’s safety, reliability theory is applied to study a structure’s failure probability due to the uncertainty (i.e., randomness) of design and production parameters with (a) variability in working conditions and the environment and (b) direct interaction with the soil, the conventional approach has been based on deterministic design methods. In contrast, using the concept of reliability as a new and useful approach, we develop the industry of design and manufacture of agricultural machinery. In this study, the first-order reliability method (FORM) was used to analyze the reliability of a plow bottom standard. To perform the reliability analysis, the required forces on the standard were determined by simulating the interaction of the plow with the soil using finite element method by Abaqus software. Random variables were considered as longitudinal and vertical forces on the bottom standard, radius of the standard arc, plastic cross-section modulus, and yield stress. The reliability index (β) as a measure of the system’s safety of was determined using reliability analysis whose value was found to be 2.569 for the bottom's standard. Moreover, the failure probability (Pf) of the bottom's standard was calculated as 0.005. In the final step, the results of FORM reliability analysis were compared with the reliability results of the Monte Carlo simulation of the plow bottom’s standard. The results showed that the bottom standard’s probability of failure in the FORM and Monte Carlo methods for the conditions considered—i.e., very compacted soil, plowing depth of 30 cm, and velocity of 3 m s-1—are low and almost low, respectively. Also due to the lack of lateral force FX in the limit state function, the FORM analysis indicated sufficient uncertainty of the bottom standard design; therefore, strengthening or optimizing this part of the moldboard plow chassis seems necessary. تفاصيل المقالة -
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137 - Dynamic Load Carrying Capacity of Flexible Manipulators Using Finite Element Method and Pontryagin’s Minimum Principle
Moharam Korayem Mostafa Nazemizadeh Hamed Rahimi nahoojiIn this paper, finding Dynamic Load Carrying Capacity (DLCC) of flexible link manipulators in point to-point motion was formulated as an optimal control problem. The finite element method was employed for modelling and deriving the dynamic equations of the system. The s أکثرIn this paper, finding Dynamic Load Carrying Capacity (DLCC) of flexible link manipulators in point to-point motion was formulated as an optimal control problem. The finite element method was employed for modelling and deriving the dynamic equations of the system. The study employed indirect solution of optimal control for system motion planning. Due to offline nature of the method, many difficulties such system nonlinearities and all types of constraints can be catered for and implemented easily. The application of Pontryagin’s minimum principle to this problem was resulted in a standard two-point boundary value problem (TPBVP), solved numerically. Then, the formulation was developed to find the maximum payload and corresponding optimal path. The main advantage of the proposed method is that the various optimal trajectories can be obtained with different characteristics and different maximum payloads. Therefore, the designer can select a suitable path among the numerous optimal paths. In order to verify the effectiveness of the method, a simulation study considering a two-link flexible manipulator was presented in details. تفاصيل المقالة -
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138 - Comparison Study on Neural Networks in DamageDetection of Steel Truss Bridge
Hassan Aghabarati Mohsen TabrizizadehThis paper presents the application of three main Artificial Neural Networks (ANNs) in damage detection of steel bridges. This method has the ability to indicate damage in structural elements due to a localized change of stiffness called damage zone. The changes in stru أکثرThis paper presents the application of three main Artificial Neural Networks (ANNs) in damage detection of steel bridges. This method has the ability to indicate damage in structural elements due to a localized change of stiffness called damage zone. The changes in structural response is used to identify the states of structural damage. To circumvent the difficulty arising from the non-linear nature of the inverse problem, three neural networks, Multi-Layer Perceptron Neural Network (MLPNN), Radial Basis Function Neural Network (RBFNN) and General Regression Neural Network (GRNN) are employed to simulate damage states of steel bridges. It was observed that the performance of all three networks is well and they have good agreement with actual results performed with Finite Element analysis. The efficiency of GRNN in structural identification is so good, although RBFNN has results close to GRNN and MLPNN results are satisfactory. All networks have good results while there is a little damage in structural members. Generally, results would have more error when damages in structural members extend. The engineering importance of the whole exercise can be appreciated once we realize that the measured input at only a few locations in the structure is needed in the identification process using neural networks. تفاصيل المقالة -
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139 - The Effect of Soccer Ball Impulse on Lower Limbs of the Human Body
Leila Shahryari Behtash JavidSharifi JavidSharifi Mohammad Ali SamianifarDespite the fact that soccer is one of the most popular sports in the world, little attention has been paid to this game scientifically which could otherwise provide a broad range of interesting outcomes. Sport equipment has a significant effect on how a game is played. أکثرDespite the fact that soccer is one of the most popular sports in the world, little attention has been paid to this game scientifically which could otherwise provide a broad range of interesting outcomes. Sport equipment has a significant effect on how a game is played. Different features of the soccer ball such as its size, structure, weight and potential incoming pressure also affect the nature and quality of the game. Different models of soccer balls have been developed with the aim of increasing game quality and performance. Many scholars have investigated the displacements during typical soccer games caused by the ball impulse and the feet, but few studies have focused on the interaction between the ball and the feet. The aim of the present study is, thus, to investigate tension development and possible deformations caused by kicking the ball. Players who are well aware of soccer rules and have a little knowledge about soccer-induced injuries easily realize that the impulse of a non-standard ball considering its material, size or weight may severely damage the knees or other body parts. Due to the importance of the issue, to evaluate the impact of the soccer ball on the footballer’s feet, two finite element models of typical soccer balls have been studied with respect to the standard features of the real soccer ball in the three layers of leather, thread and rubber. The first model is proportional to the mass of the standard ball and the second incorporates a mass less than the standard level. Two models of bones are used in the present study: a single layer bone and a two-layer bone with cortical and cancellous tissues. For better understanding of the injuries resulting from the impulse from a non-standard ball, the used finite element software employs mechanic laws of sport biomechanics to provide better understanding of the details using mathematical modeling, computer simulation and experimental measurements. In this regard, this significant point is achieved through modeling the ball impulse to the feet which is quite complex and needs some simplification. As the soccer ball is flexible, most of the force is absorbed by the model’s flexibility. In the other model with a less flexible ball, the force absorbed by the bone is significantly more. تفاصيل المقالة -
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140 - Quasi-static Axial Compression of thin-walled Circular Composite Tubes
Mohammad Mahdi Kheirikhah Sajjad Dehghanpour Mohsen RahmaniAssessing the behavior of composite structures which are subjected to impact loads is one of the important subjects in the field of mechanical sciences. Using thin-walled tubes which collapsed and absorbed the impact energy is a well-known method to prevent damages to t أکثرAssessing the behavior of composite structures which are subjected to impact loads is one of the important subjects in the field of mechanical sciences. Using thin-walled tubes which collapsed and absorbed the impact energy is a well-known method to prevent damages to the other parts of the structures. In this paper, deformations, crushing length, peak load, mean force and energy absorption capacity of thin-walled circular composite tubes are investigated both experimentally and numerically. In order to experimental study, three circular composite tubes were fabricated and subjected to quasi-static axial load. Also, a finite element model was constructed and analyzed under same conditions using FEM27 and LS-DYNA software packages. The results of simulations are in good agreement with the experimental data and show that the section geometry has considerable effect on the energy absorption. The circular composite tube has the most energy absorption capacity and the most average force among all investigated sections. تفاصيل المقالة -
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141 - Post-Tensioned Steel Connections Self-Centering Behavior Using the Finite Element Method
Mahmoudreza Shiravand Ahmadreza TorabipourDue to lack of the proper and well behavior of steel moment-resisting connections subjected to the great and major earthquakes, excessive researches have been conducted to mitigate the damages on the primary elements and connections. Therefore, elimination of residual d أکثرDue to lack of the proper and well behavior of steel moment-resisting connections subjected to the great and major earthquakes, excessive researches have been conducted to mitigate the damages on the primary elements and connections. Therefore, elimination of residual drift and increasing the plastic rotation capacity for the connectors in the panel zone are required. The main purpose of this study is to numerically investigate the behavior of the recent kind of the steel moment connections which are called as steel self-centering post-tensioned connections. The steel post-tensioned connections consisted of some high strength strands for self-centering feature plus energy dissipater angles for adjustment of plastic deformation. This paper studies on the steel self-centering post-tensioned connections using the finite element method. The obtained results are verified based on the experimental study. Accordingly, the energy dissipation, rigidity percentage, and ductility factor of the connections are determined. Results revealed the perfect self-centering with the proper ductility factor. Furthermore, it was observed that the post-tensioned steel connections have a high plastic rotation capacity without any damages to the column and beam. تفاصيل المقالة -
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142 - The effect of discrete lateral and torsional bracings stiffness on the elastic lateral-torsional buckling of mono-symmetric I beam, under the concentrated moment
E. Mohammadi J. Asgari Marnani S. Tavousi M.S. RohanimaneshWhen the out-of-plane stiffness of a beam is remarkably lower than the in-plane stiffness, the lateral-torsional buckling occurs. In this study, the behavior of mono-symmetric I-beams with discrete torsional and lateral bracings under the concentrated moment is investig أکثرWhen the out-of-plane stiffness of a beam is remarkably lower than the in-plane stiffness, the lateral-torsional buckling occurs. In this study, the behavior of mono-symmetric I-beams with discrete torsional and lateral bracings under the concentrated moment is investigated using the finite element analyses. Then, based on the numerical analyses, equation for the stiffness requirement is proposed. The results show that the location and the type of the bracing have an important role on the stiffness requirement and buckling strength. تفاصيل المقالة -
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143 - Finite Element Method for Static Cyclic Behavior of Steel Shear Wall with Corrugated Plates
Mohammad Reza Farhadi Hassan Aghabarati Hadi Niromand JaziThe system of steel shear wall is an initiative resistance system against the lateral load such as an earthquake and the wind that has been researched in the last three decades. Currently, this system is noticed more than other systems because of adequate stiffness, duc أکثرThe system of steel shear wall is an initiative resistance system against the lateral load such as an earthquake and the wind that has been researched in the last three decades. Currently, this system is noticed more than other systems because of adequate stiffness, ductility, and more energy absorption. The system of steel shear wall with corrugated sheets has been offered as an innovative system, since the construction of panels for hard-set steel shear wall is expensive and also it causes the increscent of weight construction. This type of system has been developed using of hard outer plate from geometry of corrugation shape that has better buckling strength than hard-set and flat case in this study. This study is conducted to compare the strength and energy dissipation capacity of three different steel shear walls: unstiffened, trapezoidally vertical corrugated and trapezoidally horizontal corrugated under vibration load of AISC 341-10 instruction with 100mm movement. The results reveal that although the ultimate strength of the unstiffened model is nearly 17% larger compared to that of the corrugated models, energy dissipation capacity of the corrugated models are approximately 52% larger compared to the unstiffened model. تفاصيل المقالة -
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144 - Pillow-Shape Base Isolation System and Its Seismic Behavior
Ali Tayaran Mahmood HosseiniIn this paper a new isolating system is introduced for short to mid-rise buildings. In comparison to conventional systems such as LRB and HRB, the proposed system has the advantage of no need to cutting edge technology and has low manufacturing cost. This system is made أکثرIn this paper a new isolating system is introduced for short to mid-rise buildings. In comparison to conventional systems such as LRB and HRB, the proposed system has the advantage of no need to cutting edge technology and has low manufacturing cost. This system is made up of two orthogonal pairs of pillow-shaped rollers that are located between flat bed and plates. By using this system in two perpendicular directions, building can move in all horizontal directions with respect to its foundation. Due to the pillow shape of the roller, this system has self-centering capability which causes it to return to its original position after the earthquake. The rolling friction force between pillows and their bed creates some damping in the system which prevents it from further oscillation after earthquake excitations diminish. The purpose of this study is to evaluate the proposed isolation system’s performance under different earthquake excitations. First of all general features of the proposed isolators have been introduced followed by the analytical equations of the system. Vertical bearing capacity and the effects of the thickness of pillows has been investigated using ABAQUS software. It has been shown that for a pair of pillows of 58 cm width, 45 cm height and 100 cm length the vertical load bearing capacity of the system is more than 300 tons. The period of system with respect to the height and radius of curvature of the rollers, and seismic response of a building, assumed as a rigid body resting on isolators, has been studied subjected to simultaneous effects of horizontal and vertical excitations. It has been shown that the proposed system can reduce the absolute acceleration in the building around 78% in average, while the building’s maximum displacement is around 1.77 times of the ground in average. تفاصيل المقالة -
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145 - Bending Fatigue Tests and Finite Element Models of Steel Rectangular Hollow Sections [SRHS]
islam Ezz El-Arab W GrayThe Welding in cold formed areas is not only an open question for statically loaded sections (brittle fracture) but also for dynamically loaded structures (fatigue resistance). A lot of structures are subjected to dynamic loadings and unfortunately very little informati أکثرThe Welding in cold formed areas is not only an open question for statically loaded sections (brittle fracture) but also for dynamically loaded structures (fatigue resistance). A lot of structures are subjected to dynamic loadings and unfortunately very little information about the influence of welding in the cold formed areas on fatigue resistance is available. In order to establish the fatigue behavior of welded and non-welded rectangular hollow sections specimens, a large number of 4-point bending tests are performed at the Saud Bin Laden Group SBG with cooperation with Buro Happold UK, Laboratory for Steel. Because these tests are very expensive, and because of the large number of parameters regarding the RHS to be investigated (steel grade, wall thickness, load distribution, boundary conditions), a number of finite element models for these specimens are made. By modeling the specimens with different types of finite elements (shells, solids) and taking into account some types of loading distributions and boundary conditions, the obtained results (stresses, strains, displacements) from a static analysis are compared with those obtained from the real 4-points bending tests. In this way, the obtained conclusions would lead to decrease of the number of the specimens that need to be tested as well as the costs of the project. Furthermore, by using finite element analysis, many factors with direct influence on the fatigue resistance can be considered. تفاصيل المقالة -
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146 - Free vibration analysisof soft-core composite-faced sandwich plates using three-dimensional finite element method
Mohammad Mahdi Kheirikhah Hasan Aghabarati Pooneh KhosraviIn this paper, natural frequencies of the sandwich plates with soft flexible core and composite face sheets are obtained. Three-Dimensional (3D) finite element method (FEM) is used for constructing and analyzing of the sandwich plates to obtain their natural frequencies أکثرIn this paper, natural frequencies of the sandwich plates with soft flexible core and composite face sheets are obtained. Three-Dimensional (3D) finite element method (FEM) is used for constructing and analyzing of the sandwich plates to obtain their natural frequencies. Continuity conditions for transverse shear stresses at the interfaces as well as transverse flexibility and transverse normal strain and stress of the core are considered.The effects of plate dimensions such as aspect ratio and thickness ratio are studied. Also, different boundary conditions such as all edges clamped (CCCC), all edges simply supported (SSSS) and combined boundary conditions including (CFCF)are applied to the sandwich plates. Comparison of the present results in special case with those of the accurate plate theories confirms the accuracy of the proposedmodel. تفاصيل المقالة -
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147 - The Effect of Lower Detachment Zone on Buckle Folds Geometry
O BaraniBuckle folds are common traps for hydrocarbon in several contractional provinces. Buckle folds form where stratified sequences rest a top salt or some other utterly weak rock as a decollemet zone in units with high competency contrasts by a compressive stress which acte أکثرBuckle folds are common traps for hydrocarbon in several contractional provinces. Buckle folds form where stratified sequences rest a top salt or some other utterly weak rock as a decollemet zone in units with high competency contrasts by a compressive stress which acted along the length of the rock layers. An important parameter affecting buckle folding of a competent zone above a mobile decollement is existence of a thick lower decollemet. In this paper the effect of detachment zone on folding of rock layers is studied using finite element method. Large deformation formulation is considered. Mohr-Coulomb plasticity model is used to deal with nonlinearity of material during folding. Two cases of folding are considered. In the first case a symmetric fold with equal detachment thickness beneath two flanks is analyzed. In the second case detachment zone is omitted in one flank. Finally, the effect of detachment zone on folding and deformed shape of buckle fold is studied. تفاصيل المقالة -
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148 - A Case Study of Performance Improvement of Femur Prosthesis
Leila Shahryari Behtash JavidSharifi Mehdi DabaghmaneshNowadays, the placement of artificial prostheses in human skeleton, etc. is common due to different reasons such as fractures or deficiencies. Prostheses are structures that assist the performance of organs by reconstruction of some body parts through different methods أکثرNowadays, the placement of artificial prostheses in human skeleton, etc. is common due to different reasons such as fractures or deficiencies. Prostheses are structures that assist the performance of organs by reconstruction of some body parts through different methods to enable the organ to re-obtain its performance completely or partially and, since the use of external prostheses might lead to issues such as severe traumas, slow recovery and imposition of enormous hospital costs on the patient, therefore, use of internal prostheses can be an effective method for accelerating the process of improvement for the patient. By using CT-scan photos of a 54-year-old man weighing 60 kg and with a femur length of 36 centimeters, and also using a titanium prosthesis with diameters equaling 9 and 13 mm along with screws with diameters of 4 mm whose placement are with angles of ±4, ±4 and ±36 degrees, the geometry of the model has been provided and the model has been analyzed through the finite element method. Results indicated that in case of using the prosthesis with the diameter of 13 mm and screws of 4 mm with angle of +36, the least stress will be imposed on the bone and prosthesis. تفاصيل المقالة -
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149 - Analysis of Masonry Infill Panels Retrofitted with FRP Sheets in R/C Frames
Hosein Parastesh Murat SaatciogluMasonry infill walls are often used as non-structural elements. According to the past structural failure, ignorance of interaction between infill walls and enclosed frame may lead to the different seismic response for non-ductile building frames. The main contribution o أکثرMasonry infill walls are often used as non-structural elements. According to the past structural failure, ignorance of interaction between infill walls and enclosed frame may lead to the different seismic response for non-ductile building frames. The main contribution of this paper is to analytically investigate the behavior of reinforced concrete with masonry infill panels as participating structural. In doing so, a finite element model based on an equivalent strut method is conducted to represent the behavior of masonry panels. The strut model is calibrated using the results of the companion experimental program, which examined the cyclic behavior of infill panels with and without FRP sheets. Accordingly, a nonlinear spring element and a shell element are used to simulate the behavior of masonry strut elements and FRP sheets, respectively. The nonlinear static analysis (Push over analysis) is accomplished using SAP2000 [1] structural analysis software for a 10-story building with FRP sheets subjec تفاصيل المقالة -
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150 - Finite element modeling of a pavement piezoelectric energy harvester
Ehsan Latifi Pakdehi Ali Akbar Pasha ZanoosiOne of the best methods to achieving renewable and clean energy is piezoelectric energy harvesters (PEHs), which convert mechanical and vibration energy into electrical energy. These generators appeared after the special and unique capabilities of piezoelectric and vibr أکثرOne of the best methods to achieving renewable and clean energy is piezoelectric energy harvesters (PEHs), which convert mechanical and vibration energy into electrical energy. These generators appeared after the special and unique capabilities of piezoelectric and vibration to electrical energy can be directly converted. The use of these generators is seen in many fields including the use of roads and bridges to convert vibrations caused by the vehicles in to electrical energy and other thing. In this study a piezoelectric energy harvester with the feature of parallel piezoelectric connections was computer simulated using a finite element method. In a computer simulation unlike laboratory method that can only analyze one form of a system, different states and situations of factors can be simulated. In this study, to achieve an optimal state of power and output voltage of an existing PEH, the effects and behaviors of different parameters such as forces, frequencies, temperatures, housing dimensions, piezoelectric materials and the presence of isolators have been investigated. In addition, to obtain the significance of these factors, using the analysis of variance method, the importance and effectiveness of each of these parameters has been investigated. The results revealed that increasing the amount of force and frequency and decreasing the temperature increases the output voltage of this kind of PEH. Changing the dimensions of the housing if its area is constant, does not change the output result and the use of isolators reduces the output voltage. The effect of these parameters is compared to previous studies and the results are presented. تفاصيل المقالة -
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151 - Effect of flower pattern on the curvature of high-strength steel pipe in roll forming
M. Karimi Firouzjaei H. Moslemi Naeini B. Abbaszadeh M.M. KasaeiThe geometrical characteristic of products is one of the crucial quality indicators in the cold roll forming process. In this process, an appropriate flower pattern for rolls is vital to achieve the desired geometry and quality for high-strength steel pipes. In this pap أکثرThe geometrical characteristic of products is one of the crucial quality indicators in the cold roll forming process. In this process, an appropriate flower pattern for rolls is vital to achieve the desired geometry and quality for high-strength steel pipes. In this paper, four different flower patterns, including circular, edge bending, double radius, and reverse bending are designed for the roll forming process of the high-strength steel pipe. Then, the effect of the flower pattern on the curvature distribution of the deformed strip is investigated using finite element analysis. The accuracy of the finite element model is evaluated by performing experimental tests. The results show that forming the strip with the reverse bending flower pattern leads to a more uniform curvature distribution in its cross-section, especially in the edge portion. Thus, this flower pattern design method is recommended for the roll forming process of the high-strength steel pipes. تفاصيل المقالة -
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152 - Fracture analysis of conical shells containing an internal semi-elliptical crack
C. Burvill M.M. Kheirikhah S. Omidi S. GohariConical shells play a significant role in different branches of engineering such as aerospace and oil industries. The purpose of this paper is to analyze the fracture behavior of metallic conical shells containing an internal semi-elliptical crack. An accurate three-dim أکثرConical shells play a significant role in different branches of engineering such as aerospace and oil industries. The purpose of this paper is to analyze the fracture behavior of metallic conical shells containing an internal semi-elliptical crack. An accurate three-dimensional finite element method is employed to model the conical shell using ANSYS standard code. Special singular elements are used to consider the square-root singularity at the semi-elliptical crack front. Stress intensity factors of the cracks which placed in different positions of the shell is calculated. To confirm the accuracy of the present finite element model, both stress distribution of the structure and stress intensity factor of the crack in special case are compared with published results. The effect of different geometrical parameters on the stress intensity factor of the cracks are investigated. Results show that the crack aspect ratio has a significant effect on the stress intensity factor of the cracks. تفاصيل المقالة -
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153 - Forming limit curves of AA3105 on multiple temperature conditions: numerical investigation and experimental verification
Behzad Hadiyan Ramin Hashemi Habibollah AkbariIn this paper, Forming Limit curves (FLCs) of AA3105 aluminum alloy sheet were obtained at four different temperatures using the Nakazima test. A novel approach based on the Nakazima test was applied to fabricate the experimental setup for determining forming limit diag أکثرIn this paper, Forming Limit curves (FLCs) of AA3105 aluminum alloy sheet were obtained at four different temperatures using the Nakazima test. A novel approach based on the Nakazima test was applied to fabricate the experimental setup for determining forming limit diagrams (FLDs) at elevated temperatures. First, the Nakazima-die-set was manufactured, and a thermal system was prepared for increasing sheet and die’s temperature; then AA3105 samples were tested at four different temperatures experimentally. Moreover, the ABAQUS finite element software was employed. Three different criterions including the 2nd order of derivatives for major strain, equivalent plastic strain, and thickness strain were applied to estimate the onset of localized necking. The numerical results were verified by experiment. Both the experimental and finite element method results illustrated that the level of the forming limit diagram for the aluminum sheets improved by increasing its temperature. The forming limit improvement was not equal in every strain paths. تفاصيل المقالة -
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154 - Finite element simulation of pyroplastic deformation, anisotropic shrinkage and heterogeneous densification for ceramic materials during liquid phase sintering process
Hamed Yaghoubi Esmail Salahi Fateme TaatiPyroplastic deformation is a distortion of the ceramic shape during the sintering process. It occurs because the flow of the vitreous phase at high temperature and the applied stress due to the weight of the product during sintering process. The aim of this paper deals أکثرPyroplastic deformation is a distortion of the ceramic shape during the sintering process. It occurs because the flow of the vitreous phase at high temperature and the applied stress due to the weight of the product during sintering process. The aim of this paper deals with describing a numerical-experimental method to evaluate the pyroplastic deformation, to predict the anisotropic shrinkage and heterogeneous densification for ceramic materials during the liquid phase sintering process, as a function of sintering time. For this purpose, three experimental configurations including midpoint deflection, sinter bending and free sintering test were designed; the finite element method are implemented by the CREEP user subroutine code in ABAQUS. The fair accordance between simulation results and experimental data reveals that the shear and bulk viscosity modulus as well as dynamic viscosity used in the simulation are near the real ones. The anisotropic shrinkage factor K_xy has been proposed to investigate the shrinkage anisotropy. It has been shown that the shrinkage along the normal axis of slip casting is about 1.5 times larger than that of casting direction. The inhomogeneity in Von-Misses, pressure, and principal stress intensifies the density non-uniformity in the samples. تفاصيل المقالة -
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155 - Prediction of forging force and barreling behavior in isothermal hot forging of AlCuMgPb aluminum alloy using artificial neural network
hamidreza Rezaei Ashtiani p shahsavariIn the present investigation, an artificial neural network (ANN) model is developed to predict the isothermal hot forging behavior of AlCuMgPb aluminum alloy. The inputs of the ANN are deformation temperature, frictional factor, ram velocity and displacement whereas the أکثرIn the present investigation, an artificial neural network (ANN) model is developed to predict the isothermal hot forging behavior of AlCuMgPb aluminum alloy. The inputs of the ANN are deformation temperature, frictional factor, ram velocity and displacement whereas the forging force, barreling parameter and final shape are considered as the output variable. The developed feed-forward back-propagation ANN model is trained with Leven berg–Marquardt learning algorithm. Since the finite element (FE) simulation of the process is a time-consuming procedure, the ANN has been designed and the outputs of the FE simulation of the hot forging are used for training the network and then, the network is employed for prediction of the behavior of the output parameters during the isothermal forging process. Experimental data is compared with the FE predictions to verify the model accuracy. The performance of the ANN model is evaluated using a wide variety of standard statistical indices. Results show that the ANN model can efficiently and accurately predict isothermal hot forging behavior of AlCuMgPb alloy. Finally the extrapolation ability and noise sensitivity of the ANN model are also investigated. It is found that the extrapolation ability is very high in the proximity of the training domain, and the noise tolerance ability very robust. تفاصيل المقالة -
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156 - Optimization of the strain distribution in the roll forming process using the desirability function and finite element methods
Siroos Ahmadi Vali Alimirzaloo Meysam Abdollahzade GavganiDefects of the roll forming process are affected by amount and situation of the strains distribution. The effect of the process parameters on the strain distribution in the round cross section roll forming process has been studied. Finite element and response surface me أکثرDefects of the roll forming process are affected by amount and situation of the strains distribution. The effect of the process parameters on the strain distribution in the round cross section roll forming process has been studied. Finite element and response surface method have been used for process modelling. Then desirability functions approach and overlaid counter plots have been employed for optimization of the process. Three factors included roll diameter, distance between the stations and linear speed of the sheet are considered as input parameters. Sum of longitudinal maximum strain and transverse strain distribution uniformity were taken as response functions. Response function model for each function was obtained using the RSM. Finally, optimization of the process has been done using the desirability function approach and overlaid contour plots .Results show that both of the response surface models have good model adequacy. Optimization by desirability functions approach was presented as points which according to the type of the process and production requirements can only be used to start and preliminary design. But the overlaid contour plots have flexibility in output for manufacturing processes. Output overlaid contour plots provide optimum area that there is wide range of values for choices in different condition. تفاصيل المقالة -
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157 - Upper bound and numerical analysis of cyclic expansion extrusion (CEE) process
M. M. Samandari S.H.R. Torabi Ghader FarajiDeformation of the material during cyclic expansion extrusion (CEE) is investigated using upper-bound theorem. The analytical approximation of forming loads agrees very well with the FEM results for different amounts of chamber diameter, friction factor and also for low أکثرDeformation of the material during cyclic expansion extrusion (CEE) is investigated using upper-bound theorem. The analytical approximation of forming loads agrees very well with the FEM results for different amounts of chamber diameter, friction factor and also for lower die angles. However, the difference between analytical and numerical solution increases at higher die angles which are explained by the formation of dead-metal zones at these angles. The results show that the forming load increases at higher friction coefficients, higher chamber diameters and lower amounts of corner fillet radius, but for the die angle there is a maximum value of laod at about 60o. Forming load enhanced by the increase of the die chamber diameter and friction factor. Increasing the die chamber diameter causes to higher strains and, therefore, higher rate of homogenous work. The load decreased slightly by an increase of die corner radius because of the lower and more homogeneous strain distribution in the material. تفاصيل المقالة -
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158 - Simulation of Heat Transfer and Recrystallization in Aluminum Alloy AA 6070 by TIG Welding Method
Mir Javad Mir Najd Gerami Eslam Ranjbarnodeh Mehdi FarajpourAluminum alloys have many applications in transportation industry because of their abundance, ease of production, as well as proper mechanical and physical properties. One of these alloys is obtained by combining aluminum with silicon and magnesium (Al-Mg-Si alloys). Si أکثرAluminum alloys have many applications in transportation industry because of their abundance, ease of production, as well as proper mechanical and physical properties. One of these alloys is obtained by combining aluminum with silicon and magnesium (Al-Mg-Si alloys). Since the plates of this alloy are rolled up, heat transfer and crystallization in the heat-affected zone (HAZ) is an important point in their welding. In this study, we have attempted to investigate welding-induced recrystallization in this alloy using the finite element method. For this purpose, the physics of the problem was defined and simulated using ANSYS software. In the next step, the results of theoretical (simulated) and experimental investigations were compared and the effect of current on the size of weld pool and thermal cycle of different samples was assessed. Then, through microscopic examination of different areas of the welded samples, the size of recrystallized area was measured and compared with the results of mathematical calculations. Finally, the hardness of weld zone and recrystallized area was analyzed. A temperature of 630°C and holding time of about 0.3 seconds is sufficient for recrystallization of this alloy during welding. تفاصيل المقالة -
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159 - Plastic deformation analysis in parallel tubular channel angular pressing (PTCAP)
Ghader Faraji Mahmoud Mousavi MashhadiaParallel tubular channel angular pressing (PTCAP) process is a novel recently developed severe plastic deformation technique for fabrication of ultrafine grained (UFG) metallic tubes. This new process consists of two half cycles and is affected by several parameters suc أکثرParallel tubular channel angular pressing (PTCAP) process is a novel recently developed severe plastic deformation technique for fabrication of ultrafine grained (UFG) metallic tubes. This new process consists of two half cycles and is affected by several parameters such as channel angles, deformation ratio and curvature angles. In this paper, the effects of these parameters on the plastic deformation behavior, imposed strain, strain homogeneity and the process load were investigated using finite element method (FEM). The results indicated that an increase in the channel angle leads to a decrease in the imposed strain at the end of both half cycles of PTCAP process. Investigation on the effects of the curvature angles showed that better strain homogeneity is achieved in lower curvature angles. Also, minimum required process load and the best strain homogeneity could be obtained in the curvature angle equal to zero. Study on the deformation ratio (K) revealed that the best and worse strain homogeneity could be achieved in K values equal to 0.6 and 1 respectively. From the point of view of better strain homogeneity and needing lower process loads, it could be concluded that lower K value (0.6 t0) leads to best strain homogeneity and lowest process load. تفاصيل المقالة -
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160 - Nonlinear bucking analysis of Polystyrene, Polyvinyl chloride, and Polypropylene cylindrical nano-composite shells reinforced by carbon nanotubes based on micro-mechanics and finite element methods
Reza Hosseini-Ara Mohsen AkbariIn this paper, we present nonlinear buckling instability analysis of Polystyrene, Polyvinyl chloride, and Polypropylene nano-composite shell-structures reinforced by carbon nanotubes (CNTs) under uni-axial compressive load to obtain a more conservative buckling response أکثرIn this paper, we present nonlinear buckling instability analysis of Polystyrene, Polyvinyl chloride, and Polypropylene nano-composite shell-structures reinforced by carbon nanotubes (CNTs) under uni-axial compressive load to obtain a more conservative buckling response as compared with linear analysis. For this end, the Mori-Tanaka method is firstly utilized to estimate the effective elastic modulus of composites having aligned oriented straight CNTs. Then, a novel model based on micro-mechanics and finite element method is developed for buckling analysis of a cylindrical nano-composite shell reinforced by CNTs and various effects of different types of polymer matrices (Polystyrene, Polyvinyl chloride, and Polypropylene), CNTs volume fraction, CNTs orientation angle, aspect ratio of cylinder, and different boundary conditions (simply supported and clamped ends) on critical buckling load of cylindrical nano-composite shells are discussed. The proposed model is based on Mori-Tanaka micro-mechanics which is developed in ABAQUS finite element package. Herein, numerical results show different behavior from shell-type buckling to beam-type buckling in L/R =8 due to change of the cylinder’s aspect ratios. Moreover, the developed finite element code and numerical results are compared and validated with Mori-Tanaka analytical model in available literature and shown a good agreement. تفاصيل المقالة -
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161 - A new approach for achieving excellent strain homogeneity in tubular channel angular pressing (TCAP) process
Ghader Faraji F. Reshadi M. BaniasadiaTubular channel angular pressing (TCAP) is a recently invented novel severe plastic deformation technique for producing UFG tubes. Plastic deformation analysis using the finite element method (FEM) was carried out to investigate the effects of trapezoidal channel geomet أکثرTubular channel angular pressing (TCAP) is a recently invented novel severe plastic deformation technique for producing UFG tubes. Plastic deformation analysis using the finite element method (FEM) was carried out to investigate the effects of trapezoidal channel geometry on strain inhomogeneity index (SII), strain level and required load compared to previously used channel geometries. The results showed that SII is decreased to 0.003 in the case of trapezoidal channel while they are 0.13 and 0.24 in the cases of semicircular and triangular channel types, respectively. It means that excellent strain homogeneity is achieved in TCAP processing using trapezoidal channel geometry. The required load for the trapezoidal channel was 41% lower than that for the triangular channel but it is almost the same for semicircular channel. From the point of view of better strain homogeneity and needing lower process load, TCAP processing using trapezoidal channel is an excellent technique for producing UFG tubes. تفاصيل المقالة -
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162 - 3D finite element study of temperature variations during equal channel angular pressing
Mehdi Shaban Ghazani A. vajd B. MosadegEqual channel angular pressing is the most promising method of severe plastic deformation with the capability of producing ultrafine grained materials. These materials exhibit improved mechanical and physical properties compared with their coarse grained counter parts.T أکثرEqual channel angular pressing is the most promising method of severe plastic deformation with the capability of producing ultrafine grained materials. These materials exhibit improved mechanical and physical properties compared with their coarse grained counter parts.The temperature variation in the sample during ECA-pressing is a key factor determining the final microstructure and mechanical properties of processed material. Therefore, in the present study, temperature rise and temperature distribution in the sample was studied with the aid of finite element simulation. In this regard, the effect of friction, ram speed and material type on the amount of temperature rise and also the temperature profile in the sample was investigated. Results of FEM simulations showed good consistency with the temperature data acquired in the experimental work. In addition, it was shown that the sample temperature AND THE AMOUNT OF TEMPERATURE RISE increases with the increase of friction; ram speed and work hardening coefficient of the material. تفاصيل المقالة -
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163 - Effect of Material Gradient on Stresses of Thick FGM Spherical Pressure Vessels with Exponentially-Varying Properties
Mohammad Nejad Mahboobeh GharibiUsing the Frobenius series method (FSM), an analytical solution is developed to obtain mechanical stresses of thick spherical pressure vessels made of functionally graded materials (FGMs). The cylinder pressure vessel is subjected to uniform internal pressure. The modul أکثرUsing the Frobenius series method (FSM), an analytical solution is developed to obtain mechanical stresses of thick spherical pressure vessels made of functionally graded materials (FGMs). The cylinder pressure vessel is subjected to uniform internal pressure. The modulus of elasticity is graded along the radial direction according to power functions of the radial direction. It is assumed that Poisson’s ratio is constant across the cylinder thickness. Primarily, displacements and stresses is obtained as closed-form solutions. Next, the profiles are plotted for different values of inhomogeneity constant along the radial direction. Finally, the problem was solved, using the finite element method (FEM). The obtained results of finite element method were compared with those of the analytical method. The analytical solutions and the solutions carried out through the FEM show good agreement. The values used in this study are arbitrary chosen to demonstrate the effect of inhomogeneity on displacements, and stresses distributions. تفاصيل المقالة -
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164 - Plastic deformation of 7075 Aluminum Alloy using Integrated Extrusion-Equal Channel Angular Pressing
mehdi shaban sahel gozalzadeh beitallah eghbaliGrain refinement improves the mechanical properties and formability of metals and alloys. So far, several different grain refinement methods have been proposed and studied. Severe plastic deformation is one of the most promising and efficient methods. Therefore, in the أکثرGrain refinement improves the mechanical properties and formability of metals and alloys. So far, several different grain refinement methods have been proposed and studied. Severe plastic deformation is one of the most promising and efficient methods. Therefore, in the present study the possibility of imposing a two-step severe plastic deformation (Extrusion and Equal channel angular pressing) on AA7075 alloy using a special designed die is investigated. Using this method, a very coarse grained microstructure with grain size of 94µm is refined to grain size of 7.5µm. Also, microstructural developments during severe deformation with and without preheating are investigated. Plastic strain distribution and temperature variation inside deformed samples are predicted by the use of thermal coupled displacement 3D finite element method. Results of FEM simulations clearly showes that the plastic strain distribution and temperature is non-uniform in sample and this introduces inhomogeneity in the resultant microstructure of sample at different regions. تفاصيل المقالة -
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165 - Finite Element Modeling of Strain Rate and Grain Size Dependency in Nanocrystalline Materials
Minoo TabanfardNanocrystalline materials show a higher strain-rate sensitivity in contrast to the conventional coarse-grained materials and a different grain size dependency. To explain these phenomenon, a finite element model is constructed that considers both grain interior and grai أکثرNanocrystalline materials show a higher strain-rate sensitivity in contrast to the conventional coarse-grained materials and a different grain size dependency. To explain these phenomenon, a finite element model is constructed that considers both grain interior and grain boundary deformation of nanocrystalline materials. The model consist of several crystalline cores with different orientations and grain boundary phase. The nonlinear behavior of the nanocrystalline core is implemented by a grain size dependent crystal plasticity. The boundary phase is assumed to have the mechanical properties of quasi-amorphous material. The constitutive equations for both grains interior and boundary phase are implemented into the finite-element software Abaqus. A calibration procedure was used to tune some parameters of the model with the previously published experimental data on the nanocrystalline copper. Then the model is used to predict the material behavior in various strain rates and grain sizes. The stresses obtained from these simulations match well with the experimental data for nanocrystalline copper at different strains and strain rates. Deviation from the Hall-Petch law and inverse Hall-Petch effect are also well illustrated by the model. تفاصيل المقالة -
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166 - Optimization of ECMAP parameters in production of ultra-fine grained Al1050 strips using Grey relational analysis
Peyman Keshtiban Mohammad Zadshakouyan Ghader FarajiProduction of lightweight metals with a higher strength to weight ratio is always the main goal of researchers. In this article, equal channel multi angular pressing (ECMAP) process as one of the most appealing severe plastic deformation (SPD) methods on production of u أکثرProduction of lightweight metals with a higher strength to weight ratio is always the main goal of researchers. In this article, equal channel multi angular pressing (ECMAP) process as one of the most appealing severe plastic deformation (SPD) methods on production of ultra-fine grained (UFG) materials studied. Two main routes A and C investigated by FEM and compared with each other from different aspects of view. ABAQUS commercial software used to evaluate the maximum strain, maximum required force and strain inhomogeneity index in both routes and obtained results of FEM verified by both theoretical calculations and experimental tests. It is inferred that although equivalent plastic strain (PEEQ) in route A is higher than that in route C, the strain homogeneity as a quality factor for route C is higher. So, route C selected for more investigation and optimization. Grey relational analysis used as the optimization method. Geometrical parameters taken as input variables and both inhomogeneity index and maximum required load taken as objectives. Then, the suggested tests by full factorial method were simulated by FEM. After optimization, it was concluded that the best set up belongs to experiment number 20 which the values of Φ1, ψ1 and ψ2 are 165°, 0° and 15°, respectively. Also, it is inferred that among geometrical parameters, die channel angle (Φ1) is the most effective parameter. تفاصيل المقالة -
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167 - Modeling and production of high strength Al strips by equal channel multi angular pressing method
Peyman Keshtiban Mohammad Zadshakouyan Ghader FarajiEqual channel multi angular pressing (ECMAP) process is the efficient method to enhance the productivity of ultra-fine grained (UFG) materials, by increasing process continuity and as a result decreasing process required time. Comparing repetitive ECAP method, in the sa أکثرEqual channel multi angular pressing (ECMAP) process is the efficient method to enhance the productivity of ultra-fine grained (UFG) materials, by increasing process continuity and as a result decreasing process required time. Comparing repetitive ECAP method, in the same period, the number of passes can be done by ECMAP. In this article, ECMAP of AL strips in two typical annealed and as received conditions studied, and route C was selected as multi pressing route. Values of equivalent plastic strain (PEEQ) and micro-hardness in the cross section of ECMAPed strips obtained both by FE simulations and practical tests, correspondingly. These values also used for obtaining the inhomogeneity of produced ECMAPed strips. Furthermore, mechanical property for both as received and annealed strips before and after pressing, studied experimentally. Also, load-displacement curve during ECMAP process obtained by FEM. For FEM results validation, PEEQ calculated by the analytical method, too. Results show that there is good conformity between FE, analytical and practical results. تفاصيل المقالة -
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168 - Numerical Analysis of Severe Plastic Deformation by High Pressure Torsion
mohammadreza kaji Ghader FarajiHigh-pressure torsion (HPT) is a metal processing method in which the sample is subjected to a very high plastic shear deformation. This process can produce exceptional levels of grain refinement, and provides a corresponding improvement in mechanical properties. To inv أکثرHigh-pressure torsion (HPT) is a metal processing method in which the sample is subjected to a very high plastic shear deformation. This process can produce exceptional levels of grain refinement, and provides a corresponding improvement in mechanical properties. To investigate the stress and strain distribution due to HPT process finite element simulation were conducted to investigate effective parameters. The simulation results demonstrate that the lowest effective strain obtained in the centers of the disk and the highest at the edges. Also, the mean stress varies linearly from the center of the disk to the edge region. The compressive stresses are higher in the disk centers and lower at the edges. By increasing the friction coefficient and the die angle, mean stress decrease and stress variation along the disc diameters become more homogeneous. Increasing of the pressure load leads to increase the mean stress and its heterogeneity along the disc radius. تفاصيل المقالة -
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169 - New Iteration based Algorithm for Shape Optimization of Internal and External Boundaries of the Initial Blank in the Deep Drawing Process
Hamidreza Gharehchahi Mohammad Javad Kazemzadeh-Parsi Ahmad Afsari Mehrdad MohammadiIn the deep drawing process, the optimal design of the initial blank shape has many advantages such as reducing the cost of production and waste and improving the quality of the process and thickness distribution. The deep drawing process is highly nonlinear due to the أکثرIn the deep drawing process, the optimal design of the initial blank shape has many advantages such as reducing the cost of production and waste and improving the quality of the process and thickness distribution. The deep drawing process is highly nonlinear due to the large deformation, plastic deformation of the material and the contact phenomenon. Therefore, the general solution to such problems is to use iterative methods based on numerical simulation. The present study implements a similar approach and presents a new algorithm to make geometrical corrections to the external boundaries of a blank, as well as its internal boundaries, in several iterations. A computer program was developed to automatically run these iterations to study the features of the proposed algorithm. Next, an example problem was solved, and the results are compared with other studies. The results showed that the proposed algorithm is sufficiently robust against the initial guesses for the blank, which is an advantage of the present algorithm over those from other algorithms. Because in other algorithms presented in the articles, if the appropriate initial guess is not selected, the algorithm will not converge to the answer. The proposed algorithm also has a higher convergence speed in achieving optimal blank. تفاصيل المقالة -
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170 - Continuous Grain Refinement of Pure Aluminum During Cyclic Contraction/Expansion Extrusion (CCEE) Analyses by Micromechanical-Based FE and Experimental Methods
Hossein Jafarzadeh Sina Hassan Alipouri Fard Alireza BabaeiSevere plastic deformation (SPD) has become an efficient route for producing ultrafine-grained and nanostructured high-strength metallic materials. The present study investigates the feasibility of synthesizing rod-shaped nanostructured pure aluminium samples with the n أکثرSevere plastic deformation (SPD) has become an efficient route for producing ultrafine-grained and nanostructured high-strength metallic materials. The present study investigates the feasibility of synthesizing rod-shaped nanostructured pure aluminium samples with the newly presented severe plastic deformation (SPD) method called cyclic contraction/expansion extrusion (CCEE). Also, the deformation characteristics of this process were studied using both micromechanical-based finite element simulations and experimental methods. Tensile test results showed a noticeable increase in yield and ultimate tensile strength values to 155 MPa and 191 MPa from the initial values of 56 MPa and 112 MPa, respectively, after the second pass of CCEE processing. The microhardness measurements showed a significant increase in hardness values to 61 Hv from the initial value of 27 Hv at the end of the first and second passes of CCEE. Results showed that the proposed technique is an efficient SPD method capable of imposing severe stains in the order of 20 after six repeated cycles. The constitutive micro-mechanical approach was implemented to predict microstructure evolution during CCEE processing. The UFG cylindrical aluminium samples with a mean grain size of 480 nm at the end of the first pass and 360 nm at the end of the second pass of CCEE were processed from the initial grain size of ~55 μm. The XRD-obtained grain sizes were consistent with the FEM-predicted values. تفاصيل المقالة -
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171 - Simulation of Plastic Deformation Behavior of Ti-6Al-4V Alloy by Finite Element Method
E Amini F Madadi Sh Katani M AtapoorMechanical properties of alloys have a strong relation with microstructure and determination of their behavior can lead to multiple advantages. To obtain this goal, finite element method )FEM( is one of the best ways. In this study a series of experiments were carried o أکثرMechanical properties of alloys have a strong relation with microstructure and determination of their behavior can lead to multiple advantages. To obtain this goal, finite element method )FEM( is one of the best ways. In this study a series of experiments were carried out on the produced Ti-6Al-4V to obtain its mechanical characteristics and to prepare it for photographing in micro dimensions. Next, using scanning electron microscopy (SEM), images were taken from some regions of the manufactured Ti-6Al-4V. In the next step, a method was developed to separate alpha-phases from beta-phases with a relatively high accuracy. At the end of this stage, the images were mapped into a matrix involving arrays which show the type of the phases. A code is written which maps the material matrices to the FEM model. The Gurson model is an appropriate model for simulating the damage inside the ductile material. Results of simulations obtained from SEM images show that the simulation data are in good agreement with experimental results and also analysis of simulation clearly shows that the failure always happens in boundaries between two different phases; ductile and brittle, and then growth over them to form the final failure of the material. تفاصيل المقالة -
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172 - Empirical and Numerical Study of Gas Turbine Disks under Mechanical Stress and Temperature Gradient
Rasoul Yari Yari Hamid Zarepour Aazam GhassemiGas turbine disks usually operate at very high temperatures and rotate at very high angular velocities under normal working conditions. High temperature in turbine disks causes changes in their properties. High angular velocity creates a large centrifugal force in the d أکثرGas turbine disks usually operate at very high temperatures and rotate at very high angular velocities under normal working conditions. High temperature in turbine disks causes changes in their properties. High angular velocity creates a large centrifugal force in the disk and high temperature reduces the strength of the material and causes deformation. Complexity of these parameters has turned the determination of stress distribution in gas turbine disks to one of the bottlenecks in the analysis, design and manufacturing of turbine engines. Therefore, using an applicable method for stress analysis is essential in order to better determine stress distribution in turbine disks. In this study, the finite element method (FEA) is used for predicting the behavior of rotating disks under mechanical and thermal stresses. In order to increase the certainty of simulation, gas turbine disk is first simulated and analyzed based on dimensions and loading conditions extracted from previous studies. Then, the results are compared with previous studies in order to determine the accuracy of analysis method applied in ANAQUS software. Afterwards, gas turbine disks are evaluated under both rotational movement and temperature gradient. The results show that the presence of angular velocity and centrifugal force cause expansion to the disk radius. The results show an acceptable correlation between the results of empirical and numerical studies. According to the results, the approach proposed in this study is a suitable method for analysis of the stress, temperature and displacement in turbine disks and other components with similar functions. تفاصيل المقالة -
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173 - Numerical Study of Effective Parameters in the Deep Drawing Process of a Cylindrical Cup and Comparison with Experimental Results
Hamidreza Gharehchahi Mohammad Javad Kazemzadeh-Parsi Ahmad Afsari Mehrdad MohammadiToday, metal forming is considered one of the essential methods of manufacturing and producing parts. Therefore, the more accurate knowledge of it leads the industrialists to produce higher quality parts. Deep drawing is one of the most important methods in metal formin أکثرToday, metal forming is considered one of the essential methods of manufacturing and producing parts. Therefore, the more accurate knowledge of it leads the industrialists to produce higher quality parts. Deep drawing is one of the most important methods in metal forming processes used to produce cup-shaped products. In this paper, numerical simulation of the deep drawing process based on the finite element method is performed using Abaqus software for a cylindrical cup. Then, the results obtained from numerical simulation are compared with the experimental results in the sources, and the validation of the simulation is performed. In the deep drawing process, effective parameters such as circumferential strain distribution, thickness strain distribution, and radial force distribution are extracted from numerical simulations and compared with experimental results in the sources. The effect of friction coefficient, blank holder force, and punch radius on the deep drawing process has also been investigated. Because experimental methods based on trial and error are time-consuming and costly to achieve the shape of the primary blank, researchers use numerical methods to simulate and design metal sheet forming processes such as deep drawing. It is necessary to compare the results with experimental works to validate the simulations performed by numerical methods. تفاصيل المقالة -
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174 - A New Geometry Modification Algorithm for Blank Shape Optimization in the Deep Drawing Process
Hamidreza Gharehchahi Mohammad Javad Kazemzadeh-Parsi Ahmad Afsari Mehrdad MohammadiDeep drawing is a popular process in sheet metal forming. The goal of shape optimization of the initial blank which is considered in the present work is to find the shape of the blank in a manner in which after a deep drawing process the contour of the edges of the prod أکثرDeep drawing is a popular process in sheet metal forming. The goal of shape optimization of the initial blank which is considered in the present work is to find the shape of the blank in a manner in which after a deep drawing process the contour of the edges of the produced part meets a target contour. Such problems are highly nonlinear because the simulation consists of large deformation, plastic deformation, and contact. Therefore, the general approach to solving such problems is using iterative methods which are based on numerical simulation. Such an approach is also followed in the present work and a new algorithm for geometry modification of initial blank in each iteration is proposed. In the proposed algorithm, the normal distance between the final contour and target contour is used as a criterion to modify the initial blank. To evaluate the proposed algorithm a computer program is developed and to automatically execute the iterative process. One numerical example solved and the results are compared with those reported in the literature. One of the benefits of the proposed algorithm is its insensitivity to the initial guess. Therefore, to evaluate the effect of the initial guess on its performance the example was solved using different initial guesses. The results show that the proposed algorithm is robust regarding the initial guess and convergence to the optimum shape will be achieved by starting from an initial guess. تفاصيل المقالة -
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175 - A Numerical Investigation the Effects of the Voltage on the Displacement and Stress of Copper-based Ionic Polymer-Metal Composites
Hamid Soleimanimehr Amin NasrollahIonic polymer material composites (IPMCs) are a group of polymeric material which deform by applying voltage and the movement of cations of polymer; it should be mentioned that the finite element method using electromechanics equations can be used to analyze these types أکثرIonic polymer material composites (IPMCs) are a group of polymeric material which deform by applying voltage and the movement of cations of polymer; it should be mentioned that the finite element method using electromechanics equations can be used to analyze these types of problem and measure the deformation. This phenomenon can causes bending and internal stress. This research, it is tried to investigate the displacement and stress of IPMC by modeling and finite element method analysis. Firstly, a 2D IPMC is designed; then the materials are applied which are cooper for the electrodes and Nafion for the polymeric core. After applying boundary conditions and meshing, the results have been analyzed by the finite element method. It is found that the relation between voltage and its effect on the bending displacement of IPMC is direct. The conclusions include the maximum displacement of IPMC membrane under the voltage of 5V is 0.42 mm and the maximum Von Mises stress on the electrode is gained 3.29×1016 (N/m2). تفاصيل المقالة -
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176 - Mechanical Stability of RCSed and ECAPed Intramedullary 316L Stainless Steel Nails in the Treatment of Diaphyseal Bone Fractures
Abdolreza Rastitalab Salar Khajehpour Ahmad Afsari Shahin Heidari Javad DehghaniOver the last several decades, implants have been used to treat fractures and promote healing. The most important reason for deformation and shortening of the bone during healing due to loading on the nails is a lack of strength of the intramedullary nail. Materials wit أکثرOver the last several decades, implants have been used to treat fractures and promote healing. The most important reason for deformation and shortening of the bone during healing due to loading on the nails is a lack of strength of the intramedullary nail. Materials with very fine grain dimensions are considered for such purposes. Ultrafine-grained (UFG) materials have structural elements with very fine grain sizes. Several methods for producing UFG materials have been developed, one of which is the top-down approach, which refines coarse-grained metals via severe plastic deformation (SPD). The SPD technique has several advantages that set it apart from other methods of synthesizing. Two of the SPD methods used in this study were the repetitive corrugation and straightening (RCS) process and the equal channel angular pressing (ECAP) process on a 316L stainless steel rod. Mechanical tests were performed on the rods produced using these methods. Under loading, simulation results revealed that the bone implanted by the RCS rod has greater structural stiffness than the bone implanted by an ECAPed 316L stainless steel rod. تفاصيل المقالة -
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177 - An Investigation of Using RCS-processed Intramedullary Stainless Steel 316L Nail in the Treatment of Diaphyseal Bone Fractures
Abdolreza Rastitalab Salar Khajehpour Ahmad Afsari Shahin Heidari Javad DehghaniThe method of intramedullary nailing, which leads to the alignment of the diaphyseal broken bone, is one of the diaphyseal fractured bone healing novelties. The rods utilized must be strong enough to withstand the forces exerted by the transplanted bone. Today, various أکثرThe method of intramedullary nailing, which leads to the alignment of the diaphyseal broken bone, is one of the diaphyseal fractured bone healing novelties. The rods utilized must be strong enough to withstand the forces exerted by the transplanted bone. Today, various researchers are interested in using severe plastic deformation (SPD) methods to improve the mechanical characteristics of metals. One of the SPD procedures used in this study was repetitive corrugation and straightening (RCS) on a 316L stainless steel rod. After conducting mechanical characteristics tests on the rods produced using this approach, ABAQUS software was utilized to simulate the intramedullary nailing finite element method (FEM). The results of the experiments revealed that raising the number of pressing stages to eight significantly increases the hardness of the samples. The simulation findings revealed that the bone sample implanted by the rod manufactured by the aforementioned procedure has a higher structural hardness than the bone implanted by a basic 316L stainless steel rod under various stress conditions. تفاصيل المقالة -
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178 - Thermal and Stress Analysis in Butt, T-shaped and Tubular Joints in the Welding Process of Dissimilar Parts
Adel Tavabe Behdad Jahanbeen Seyed Mohammad Reza Nazemosadat Ahmad AfsariConnecting parts through welding as permanent connections can play an important role in various industries. Despite the favorable load-bearing capabilities of joints resulting from welding dissimilar parts, they have some limitations that need to be identified and check أکثرConnecting parts through welding as permanent connections can play an important role in various industries. Despite the favorable load-bearing capabilities of joints resulting from welding dissimilar parts, they have some limitations that need to be identified and checked to optimize their use. One of the limitations is the behavior of parts under thermal stresses caused by the welding process. Thus, it is important to consider the welding conditions of the dissimilar parts in the contact area of the electrode and the welding seam, as this can significantly affect the mechanical performance of the welds. The research conducted in this study involved using the electric welding method with non-consumable tungsten electrodes under shielding gas (TIG) to connect aluminum and carbon steel parts. Ansys software was utilized to investigate the effect of thermal stress in the welding process for different joints. To ensure accuracy, parts were welded together practically under similar conditions, and the results obtained were compared with the results of the modeled method. First, the behavior of a steel sheet under the butt and Tee Joint and then the role of various factors on welding performance were investigated by modeling the process for a pipe in different conditions. Finally, due to the significant role of T-shaped joints in various industries, heat distribution, behavior, and stress analysis were investigated. تفاصيل المقالة -
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179 - Evaluation of Stability and Reliability of Motorized Unilateral External Fixator, Designed and Simulated using Finite Element Method to Treat Bone Fractures and Bone Loss
Alireza Bahramkia Mehran Fakhraie Salar Khajehpour Seyed Mohammad Tahami Raheb GholamiToday, it is common to align broken bones using external bone fixators; ease of installation and adjustability are among the advantages of unilateral external bone fixators compared to circular and horseshoe models. The present study aimed to ensure the stability and st أکثرToday, it is common to align broken bones using external bone fixators; ease of installation and adjustability are among the advantages of unilateral external bone fixators compared to circular and horseshoe models. The present study aimed to ensure the stability and strength of the motorized unilateral external bone fixator, equipped with four motors designed in SolidWorks software. The device was simulated and analyzed using the finite element method in Ansys software. The results were as follows: Simulation of compressive, bending, and torsional forces and reliability evaluation using the finite element method in each simulated experiment. The designed device has the necessary stability, rigidity, and desirable reliability to fix the long broken bones in place, with the possibility of displacing the bone when having a lost part. Precise bone displacement is possible since the device has four independent motorized units based on the patient's needs and the instructions of a specialist to rebuild bones. تفاصيل المقالة -
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180 - CAD Model and Finite Element Analysis of a Knee Brace for General Applications
Shayan Babaeifard Mohammad Saadat Amirhossein BadamiOne of the main problems in sports medicine in today’s world is knee injuries. Champions of various sports fields often suffer from common knee injuries, such as injuries to the anterior cruciate ligament, middle cruciate ligament, medial collateral ligament of th أکثرOne of the main problems in sports medicine in today’s world is knee injuries. Champions of various sports fields often suffer from common knee injuries, such as injuries to the anterior cruciate ligament, middle cruciate ligament, medial collateral ligament of the knee, or meniscus. In this paper, a knee brace for general applications is modeled and its stress and strain analysis is calculated with the help of software. First, the displacement of the knee brace with ABAQUS software is investigated. By moving toward the top of the knee brace, the amount of displacement decreases. So that at least the amount of displacement is in the upper part of the knee brace. In the next part, the amount of strain and strain for this knee brace is investigated. The amount of stress in the upper part of the knee brace is higher than in other places. Additionally, the amount of strain for this knee brace is determined, the knee brace in the upper part, on the inner side of the knee brace, bears more strain. The results show that this knee brace can be easily produced and considered for different applications. تفاصيل المقالة -
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181 - Experimental and FEM Analysis of Ribs Defects on Composite Lattice Cylindrical Shells
Amin Kolahdooz Seyyed Ali Latifi RostamiIn this study, the behavior of a composite lattice cylindrical shell is investigated in the buckling deforming. Also, the distribution of shell buckling response and the stress field is studied after making some defects on the ribs.Therefore using ANSYS software, a 3D f أکثرIn this study, the behavior of a composite lattice cylindrical shell is investigated in the buckling deforming. Also, the distribution of shell buckling response and the stress field is studied after making some defects on the ribs.Therefore using ANSYS software, a 3D finite element model of the shell has been created for the analysis. Material properties and geometrical data of the shell are obtained from the some experimental tests. In fact, these parameters have been extracted from the prototypesthat made with filament winding method. The parameters studied in this study include of the kind of ribs defects on buckling response and the geometrical ratios. Composite shells have been tested under axial force and obtained results are compared with the results of FEM. Based on the parametric study, the structural strength-to-weight ratio is increased around %50 by increasing the thickness of the outer shell. It is observed that in each consecutive buckling test, the buckling load is reduced; however the failed sample had reasonably good resistance to the applied load. تفاصيل المقالة -
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182 - Analytical, Experimental and Finite Element Investigation of Internal Pressure Effect in Hydroforming Process on Metallic Bellows Produced from Thin Wall Tube of Austenitic Stainless Steel Grade 316L
Mehdi Arabbeigi Mehran Moradi Boozarjomehr Ghasemi Majid SattarOne of the bellows producing method is hydroforming process .Whereas some factor of hydroforming process specially internal pressure affects on final characteristics produced bellows such as bursting, wrinkling and wall thickness distribution. In this paper the effect o أکثرOne of the bellows producing method is hydroforming process .Whereas some factor of hydroforming process specially internal pressure affects on final characteristics produced bellows such as bursting, wrinkling and wall thickness distribution. In this paper the effect of internal pressure factor in final quality of produced bellows will be investigated. In simulation of process, ABAQUS/Explicit version 6.9 code was used, and also experimental examinations for investigation the effect of this factor has done. The results obtained from methods of analytical, finite element and experimental in this paper has good agreement with each other. Also, the conclusions of this research for prediction of suitable forming pressure could be used as a basis of designing a new type of metal bellows. تفاصيل المقالة -
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183 - Using Rubber Pad Forming Process for Local Compression in Assembling of Vehicle Structure Tubes
Meysam Darvishi Mohammad Sedighi Mehrdad KhandaieNowadays, tube bonding in vehicles structure is noticeably considered by many researches. In this paper, local tube compression process by a rubber ring has been studied. Firstly, simulation of the process was performed by FEM. Then, experimental test has been carried o أکثرNowadays, tube bonding in vehicles structure is noticeably considered by many researches. In this paper, local tube compression process by a rubber ring has been studied. Firstly, simulation of the process was performed by FEM. Then, experimental test has been carried out to validate the numerical results. Numerical and experimental results were compared showing a good agreement. In the second part of this study, tube assembling of a two tubes was examined by a rubber ring. The simulation results have presented including stress distribution of both tubes. Finally, this method was compared with other tube assembling methods by observation of tube profile deformation. تفاصيل المقالة -
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184 - The Optimization of the Effective Parameters of the Die in Parallel Tubular Channel Angular Pressing Process by Using Neural Network and Genetic Algorithm Methods
Amin Armanian Hassan Khademi ZadehOne of reasons that researchers in recent years have tried to produce ultrafine grained materials is producing lightweight components with high strength and reliability. There are disparate methods for production of ultra-fine grain materials,one of which is severe plas أکثرOne of reasons that researchers in recent years have tried to produce ultrafine grained materials is producing lightweight components with high strength and reliability. There are disparate methods for production of ultra-fine grain materials,one of which is severe plastic deformation method. Severe plastic deformation method comprises different processes, one of which is Parallel tubular channel angular pressing. The aim of this study is optimizing parameters of the noticed process die just by utilizing neural network and genetic algorithm methods that at first for this purpose, by using ABAQUS finite element software, the numerical analysis of the die parameters is performed and the impact of each die parameter on the force of the process and the equivalent strain is examined. Finally, for gaining optimal parameters, MATLAB and neural network optimization methods and genetic algorithm are used. The use of neural network and genetic algorithm illustrated that to achieve the ideal possible situation in order to achieve a flawless super-fine tube, it is imperative to use the friction coefficient of 0.05, tube length of 40 mm, channel angle of 140 degrees and diameter increase difference of 1.5 mm. With such values, strain fluctuations reach 0.23, lowest value, and also the force reaches 0.49 KN and the amount of applied strain reaches its highest value to 2.37. تفاصيل المقالة -
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185 - Analytical and Numerical Investigation of Significant Parameters on Strength of Electromagnetically Assembled Products Joints
Mehdi Zohour Bahman GhorbaniElectromagnetic forming is a high energy rate forming process. In this process, an electromagnetic Lorentz body force is used for deformation of products. In this article, Electromagnetic forming process was simulated for assembly of parts as an innovative method. In th أکثرElectromagnetic forming is a high energy rate forming process. In this process, an electromagnetic Lorentz body force is used for deformation of products. In this article, Electromagnetic forming process was simulated for assembly of parts as an innovative method. In this research work, the effect of important parameters of process such as discharge energy, radius and width of rectangular groove on the strength of assembled products were studied by using finite element technique and design of experiment. After introducing the governing equations, the output of these equations were applied in simulation as a pressure on work-piece. In this simulation, an axisymmetric model was used in analysis and Johnson-Cook theory was applied due to high strain rate to show the plastic behavior of materials. Finally, the numerical results were compared with the experimental results reported by other researchers and found a good correlation between them. As a result, the bead depth increases with the increase of the discharge energy and more filling groove, increasing strength of joint. In addition, Strength of joint increases, due to create partial shearing of the tube at the groove edge and interference stresses at the tube and mandrel interface. تفاصيل المقالة -
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186 - Numerical/Experimental Analysis of the Deformation of Tubes under Concentrated Load
Javad Jafari Fesharaki Omid Rejali Seyed Ghasem MadaniDistortion and deformation of tubes during machining operations are very important. In this study, a tube used in magnetic drum separator under concentrated load (machining load) is considered. Using finite element simulation, deformities and their dependence on paramet أکثرDistortion and deformation of tubes during machining operations are very important. In this study, a tube used in magnetic drum separator under concentrated load (machining load) is considered. Using finite element simulation, deformities and their dependence on parameters such as the thickness of the tube and the place of concentrated force are observed and predicted. To compare and confirm the results, some experimental tests are considered. The results show that there is good agreement between the numerical and experimental data. The results of this study indicate the amount of residual stress in the tube by changing the location of the load, the effect of residual stresses in the tube, indentations at different levels of thickness and location of the load. Results show that the values and location of force affect the stress and residual stress in the thickness of tube. In addition, increasing the thickness of tube decreases the residual stress area in longitudinal and circumferential direction of tube. Also, the maximum residual stress in tube is occurring under the force area and by increasing the thickness of tube, the displacements of area under the force is decreased. تفاصيل المقالة -
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187 - Analytical and Numerical Investigation of Significant Parameters on Strength of Electromagnetically Assembled Aluminum Tube Joints
Mehdi Zohoor Bahman GhorbaniElectromagnetic forming is a high energy rate forming process in which an electromagnetic Lorentz body force is used for deformation of products. In this article, electromagnetic forming process was simulated for the assembly of parts as an innovative method. The effect أکثرElectromagnetic forming is a high energy rate forming process in which an electromagnetic Lorentz body force is used for deformation of products. In this article, electromagnetic forming process was simulated for the assembly of parts as an innovative method. The effect of important process parameters such as discharge energy, radius and width of rectangular groove on the strength of the assembled products were studied by using finite element technique and design of experiment. After introducing the governing equations, the output of these equations were applied in simulation as a pressure on work-piece. In this simulation, an ax symmetric model was used in analysis and Johnson-Cook theory was applied due to high strain rate to show the plastic behavior of the materials. Finally, the numerical results were compared with the experimental ones reported by other researchers and a good correlation was found between them. Results revealed that the bead depth increases with the increase of the discharge energy and more filling groove, increasing strength of joint. Also Strength of joint increases due to the creation of partial shearing of the tube at the groove edge and interference stresses at the tube and mandrel interface. تفاصيل المقالة -
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188 - Deformation of Al Alloy during Integrated Extrusion and ECAP: A Simulation Research
Ankit Sahai Shanti S. Sharma Suren N. DwivediBulk nanomaterial have several applications in automobile, aerospace, medical and manufacturing applications. These are produced by subjecting materials to severe plastic deformation (SPD) and have widely emerged as a technique for grain refinement in Al, Cu, Ti, Mg all أکثرBulk nanomaterial have several applications in automobile, aerospace, medical and manufacturing applications. These are produced by subjecting materials to severe plastic deformation (SPD) and have widely emerged as a technique for grain refinement in Al, Cu, Ti, Mg alloys with improved mechanical properties. Equal Channel Angular Pressing (ECAP) is one such SPD technique employed to produce bulk ultra-fine grained (UFG) materials by introducing a large amount of shear strain into the materials without changing the billet shape or dimensions. FE (Finite Element) modeling of SPD processes has become an important tool for designing feasible production processes, because of its unique capability to describe the complex geometry and boundary conditions. In this proposed work, integrated SPD processes namely Extrusion + ECAP (Ex-ECAP) is proposed and the specimen is subjected to these processes in the same die set-up. The 3D finite element modeling of Al6061 was performed using metal forming software FORGE. The dies used in both the processes during the simulation of Al6061 billet include a channel angle of 900 and outer corner angle fixed at 160 with simulation performed for different plunger velocities. The simulation results depict the change in equivalent strain in the entire specimen on account of these processes. The evolution of strain at different considered cross-sections is analyzed. Also, the variation in extrusion force and energy are studied for the considered process parameters. The FE simulations greatly help in designing the dies for various experimental conditions to produce bulk nanomaterial. تفاصيل المقالة -
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189 - A Study on the Forming of Sheet Metal Parts Using Multi-Point Forming Technology
Vahid Rikhtehgar Nezami Behrooz Zareh Abbas Vafaee SefatIn recent years, in order to reducing die design and manufacturing costs, Multi point forming technique has gained an increasing interest because of its high flexibility. In this process, the conventional fixed shape solid die sets are replaced with a pair of opposite m أکثرIn recent years, in order to reducing die design and manufacturing costs, Multi point forming technique has gained an increasing interest because of its high flexibility. In this process, the conventional fixed shape solid die sets are replaced with a pair of opposite matrices of controllable elements. In this paper, the fundamental principles of multi-point forming was described and the possibility of forming the one sheet metal part by this technique was investigated experimentally and analyzed using finite element simulation. Wrinkles and dimples are the most typical defects in multi-point forming of sheet metal. By the proper selection of process parameters the sound cup with good surface quality and uniform thickness distribution can be formed. The results obtained demonstrated that multi-point forming technology can be used as an effective and economic tool to the forming of single parts with different shapes and is cost-effective. تفاصيل المقالة -
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190 - Numerical and Experimental Study of Residual Stress Measurement and Thickness Distribution of T-shape Steel Tube Produced by Tube Hydroforming
Javad Shahbazi Karami Gholamhasan Payganeh Mohsen KhodsetanTube hydroforming (THF) process is used to produce the complex components from the initial cylindrical tubes. In this paper, T- shape component was formed using a tube hydroforming machine and the residual stresses of hydroformed tube was determined by hole drilling met أکثرTube hydroforming (THF) process is used to produce the complex components from the initial cylindrical tubes. In this paper, T- shape component was formed using a tube hydroforming machine and the residual stresses of hydroformed tube was determined by hole drilling method. Subsequently, the thickness distribution and residual stresses of final tube were investigated using experimental and finite element (FE) methods. The results represented the top of the protrusion has the minimum thickness, whereas the maximum thickness appears in the bottom zone of T-shape tube. The FE results showed that the maximum principal stress in the middle part of piece has own maximum value while the maximum value of minimum principal stress is located in the top of protrusion and the fillet transition region of the protrusion. It is found that the value of residual stress, protrusion height and thickness distribution in simulated results were in good agreement with the experimental results. تفاصيل المقالة -
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191 - Numerical Analysis of the Effect of Sinusoidal Pressure Path on Thinning of Tube in Hot Metal Free Bulging Process
Ali Talebi Anaraki Mohsen Loh-MousaviLight-weight and high strength alloys such as Al-Mg alloys are used in order to reduce the weight of industrial components. However these materials should be formed at elevated temperatures due to their poor formability at room temperature. Hot metal gas forming is one أکثرLight-weight and high strength alloys such as Al-Mg alloys are used in order to reduce the weight of industrial components. However these materials should be formed at elevated temperatures due to their poor formability at room temperature. Hot metal gas forming is one of the high-tech forming processes that is used to solve this problem. Recent investigation on tube hydroforming showed positive effect of oscillation of pressure paths in improving the formability of tubes. In this study, the effects of a sinusoidal pressure path on tube wall thinning of an Al6063 tube in HMGF processis investigated and the results are compared with equal constant pressure by the finite element method.Moreover, the effect of stroke on thickness reduction of the tube is also investigated. The results show that the proposed sinusoidal pressure paths have an obvious improvement of thinning in hot metal gas bulging of tube and some defects such as necking and bursting are prevented by the oscillation of the inner pressure. تفاصيل المقالة -
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192 - Finite Element Modeling and Experimental Study of the Spline Tube Forming
Masoud Feizi Reza Jafari NedoushanMetal forming processes, compared with machining ones, reduce production steps and increase manufacturing speed in addition to saving raw material. In this paper, forming process of column of a steering mechanism is investigated by finite element analyses and experiment أکثرMetal forming processes, compared with machining ones, reduce production steps and increase manufacturing speed in addition to saving raw material. In this paper, forming process of column of a steering mechanism is investigated by finite element analyses and experimental tests; and optimum die design parameters are found. Forming process parameters including die opening angle, bearing length, clearance between work piece, die and friction coefficient were studied. Some new ideas were also used in manufacturing process of dies with compression tube forming process. Without using an appropriate lubricant, friction coefficient between die, tube, the probability of tube distortion and tube bulging increased significantly. The forming force is also strictly dependent on friction coefficient and it also increases with increasing bearing length of the die. The manufactured sample had good agreement with the original drawing of profile appearance and dimensions. Effects of die and tube clearance on the required force and final part surface quality are also investigated. تفاصيل المقالة -
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193 - Simulation of a Microgripper with Electrothermal Actuator Using COMSOL Software Based on the Finite Element Method
Amin Rouhani Esfahani Mojtaba Kolahdouzan Mehran MoradiMicro-electro-mechanical systems (MEMs) are Combination of electrical and mechanical components in Micron dimensions. In recent years, holding, actuating methods and handling of MEMs components such as microgripper, microsensors and etc. have been deeply studied. Microg أکثرMicro-electro-mechanical systems (MEMs) are Combination of electrical and mechanical components in Micron dimensions. In recent years, holding, actuating methods and handling of MEMs components such as microgripper, microsensors and etc. have been deeply studied. Microgrippers for handling, positioning and assembling of micro components are very useful so that for clamping need actuation created using electrostatic, electrothermal, and electromagnetic actuators. In this paper, a new design of an electrothermal microgripper with U-shape actuators for holding and carrying a wide range of parts at the same time, For voltages corresponding between 1 to 10 volts, have been fabricated. The microgripper is made of silicone with thickness of 25 microns, and pieces between 460 to 480 microns that can hold it. The behavior of the microgripper in Multi physics powerful finite element software (COMSOL) was evaluated and the displacements of arms hold and heat generations have been simulated. تفاصيل المقالة -
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194 - Finite Element Simulation of Hydrostatic Extrusion Process to Produce Thin Bimetallic Parts
Hamid Montazerolghaem Ali DelfaniThe hydrostatic extrusion is a new method of extrusion process. The most important advantage of this method is reduction of friction and close tolerance for the coating thickness. In this study, the hydrostatic extrusion simulation of bimetallic wires has performed usin أکثرThe hydrostatic extrusion is a new method of extrusion process. The most important advantage of this method is reduction of friction and close tolerance for the coating thickness. In this study, the hydrostatic extrusion simulation of bimetallic wires has performed using of finite element method. In the following the advantages of hydrostatic extrusion compared to the direct extrusion are presented.It can be concluded that by increasing the friction coefficient between the work piece and the die, the extrusion force value also increases. Increasing the cross-section reduction when the die angle kept constant as a result of increase in die length, consequently leads to an increase in the extrusion force.Regarding to the absence of friction in the die and almost uniformly deformation and homogeneous in the hydrostatic extrusion, the product with a uniform coating thickness can be obtained as it is very important for manufacture of very high length bi-metal products. تفاصيل المقالة -
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195 - Experimental Investigation and Analysis of Manufacturing Wind Turbine Blades Produced by Hydroforming of Aluminum Alloy AA5754
Javad Shahbazi Karami Hamed Bakhtiarizade Mohsen ShahmoradiDevelopment of new technologies and combined with creativity and innovation, plays the fundamental role in developing of any community′s value. Thus, in this research the design and production of hydroforming device was introduced. One of the best and most efficie أکثرDevelopment of new technologies and combined with creativity and innovation, plays the fundamental role in developing of any community′s value. Thus, in this research the design and production of hydroforming device was introduced. One of the best and most efficient technologies in the world of metal forming is wind turbine blade producing with hydroforming method which seems as an innovative manner in this field. The aim of this paper is design a small wind turbine blade. Application of this blade is for spaces with size limitation and building large-scale wind turbines. The first step of design process involves choosing and determining the airfoil blade wind turbine, distributing along the radius, angle of the airfoil and chording length distribution along the radius. Turbine blades modeled in CATIA software and transferred to finite element software, ABAQUS. Critical blades points under the hydrostatic pressure have been identified and outputs such as displacement, Von Misses stress obtained from hydroforming simulation process. In the final stage, after ensuring the software outputs blade has been modeled and produced. تفاصيل المقالة -
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196 - Stress Concentration Factor in a Functionally Graded Material Plate around a Hole
Javad Jafari Fesharaki Seyed Ghasem Madani Davood SeydaliStress concentration factors have been examined in a functionally graded material (FGM) plate withcentral holes in different shapes in this essay. The material properties change along the thickness ofplate. ABAQUS software has been utilized for modeling of problem in wh أکثرStress concentration factors have been examined in a functionally graded material (FGM) plate withcentral holes in different shapes in this essay. The material properties change along the thickness ofplate. ABAQUS software has been utilized for modeling of problem in which subroutine ofABAQUS sub-program was used for modeling of the targeted material. The considering shapes forhole in plate are circular and elliptical in which stress concentration factors have been studied indifferent modes in respective of ellipse diameters. Similarly, stress concentration factors have beenanalyzed in the plate for various coefficients of FGM function. The results show that changes inmaterial properties and the shape of hole in plate affect the stress concentration factor around thehole. An experiment was implemented to determine verification of results from Finite ElementMethod (EFM). تفاصيل المقالة -
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197 - یک رویکرد جدید برای طراحی سیستم ارتینگ با استفاده از روش اجزاء محدود
سجاد صمدی نسب فرهاد نامداری محمد بخشی پورحفاظت از تجهیزات، ایمنی افراد و تداوم تامین برق از اهداف اصلی سیستم زمین هستند. برای طراحی دقیق سیستم زمین، تعیین توزیع پتانسیل بر روی سطح زمین و مقاومت معادل سیستم ضروری است. آگاهی از چنین پارامتر هایی اجازه بررسی امنیت ارائه شده توسط سیستم زمین، هنگامی که خرابی در سیس أکثرحفاظت از تجهیزات، ایمنی افراد و تداوم تامین برق از اهداف اصلی سیستم زمین هستند. برای طراحی دقیق سیستم زمین، تعیین توزیع پتانسیل بر روی سطح زمین و مقاومت معادل سیستم ضروری است. آگاهی از چنین پارامتر هایی اجازه بررسی امنیت ارائه شده توسط سیستم زمین، هنگامی که خرابی در سیستم های قدرت وجود دارد را می دهد.یک روش جدید برای طراحی سیستم ارتینگ با استفاده از روش اجزاء محدود (FEM) در این مقاله ارائه شده است. در این روش، تاثیری که رطوبت و دما بر رفتار مقاومت مخصوص زمین دارند در طراحی سیستم ارتینگ در نظر گرفته شده است. سیستم ارتینگ در دو حالت الکترود میله عمودی و الکترود نوع صفحه ای دفن شده در زمین در نظر گرفته شده است. مقاومت سیستم زمین، عامل بسیار مهمی در فرایند طراحی است که با استفاده از روش اجزاء محدود محاسبه می شود. روش المان محدود برای حل معادله دیفرانسیل با مشتقات جزئی حاکم بر رفتار سیستم استفاده شده است.4.4 COMSOL Multiphysics یکی از بسته هایی است که با FEM کار می کند و به عنوان یک ابزار در این طراحی مورد استفاده قرار گرفته است. در نهایت به منظور صحت نتایج ارائه شده، مقادیر مقاومت طراحی شده توسط COMSOL Multiphysics با مقادیر فرمول تحلیلی اثبات شده برای مقاومت زمین، مقایسه شده است. تفاصيل المقالة -
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198 - طراحی روتور در موتور سوئیچ رلوکتانس به منظور تولید گشتاور پیوسته بوسیله ی آنالیز اجزای محدود
داوود کرمعلیان بهروز مجیدی محمدرضا یوسفیویژگیهای الکتریکی، مکانیکی، قابلیت اطمینان بالا و همچنین سادگی ساخت و نگهداری موتورهای سوئیچ رلوکتانس باعث استفاده‌ی گسترده از این نوع موتور در صنعت شده‌است. با این حال عمده‌ترین مشکلات این موتور داشتن گشتاور ناپیوسته در برخی از زوایای گردش روتور و عدم راه‌اندازی می‌با أکثرویژگیهای الکتریکی، مکانیکی، قابلیت اطمینان بالا و همچنین سادگی ساخت و نگهداری موتورهای سوئیچ رلوکتانس باعث استفاده‌ی گسترده از این نوع موتور در صنعت شده‌است. با این حال عمده‌ترین مشکلات این موتور داشتن گشتاور ناپیوسته در برخی از زوایای گردش روتور و عدم راه‌اندازی میباشد. در این مقاله به منظور افزایش ناحیه‌ی گشتاور مثبت و از بین بردن ناحیه‌ی بدون گشتاور موسوم به ناحیه‌ی مرده1، ساختار جدیدی از روتور ارائه شده است تا علاوه بر اینکه فاصله‌ی هوایی را ثابت نگه دارد، مشکل پیوستگی گشتاور را تحت بارهای بزرگ برطرف نماید. در این روش با ایجاد برش در روتور تحت دو فاکتور مکان و زاویه‌ی برش، اندوکتانس متغیری ایجاد می‌شود که گشتاور تولیدی را به دو بخش مجزا تقسیم‌بندی می‌کند و بازه‌ی تولید گشتاور مثبت بیشتر می‌شود به صورتی که همپوشانی گشتاور مثبت بین دو فاز بوجود می‌آید. به منظور تأیید این ساختار، بهینه‌سازی متغیرهای فوق و مشاهده‌ی خروجی‌های موتور از روش شبیه‌سازی آنالیز اجزای محدود استفاده و ملاحظات ساخت نیز مورد توجه قرار گرفته است. تفاصيل المقالة -
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199 - تحلیل نیروهای الکترومغناطیسی ترانسفورماتور تحت شرایط فرورزونانس در اثر اتصال‌کوتاه سه فاز متوالی با استفاده از روش المان محدود
علی احمدپور سیدجلال سیدشنوا عبدالمجید دژم خوی الهام مکرمیاندر این مقاله، از روش تحلیلی اجزای محدود برای مطالعه پدیده فرورزونانس از دیدگاه نیروهای الکترومغناطیسی وارد بر سیم‌پیچی‌های ترانسفورماتور استفاده شده است. بهمنظور مدلسازی این پدیده، یک خطای اتصال کوتاه سه فاز متوالی در سمت اولیه و در فاصله نسبتا دور از ترانسفورماتور د أکثردر این مقاله، از روش تحلیلی اجزای محدود برای مطالعه پدیده فرورزونانس از دیدگاه نیروهای الکترومغناطیسی وارد بر سیم‌پیچی‌های ترانسفورماتور استفاده شده است. بهمنظور مدلسازی این پدیده، یک خطای اتصال کوتاه سه فاز متوالی در سمت اولیه و در فاصله نسبتا دور از ترانسفورماتور درنظر گرفته شده است. سپس با توجه به ظرفیت خازنی معادل خط، بین محل خطا تا محل نصب ترانسفورماتور، خطاهای اتصال کوتاه تک فاز به‌صورت متوالی تولید می‌شوند. به‌علت کلیدزنی، برای قطع خط در محل خطا، پدیده فرورزونانس در سیستم قدرت به‌وجود می‌آید. در نتیجه، اندازه ولتاژ و جریان‌های سمت اولیه و ثانویه ترانسفورماتورها به‌صورت محسوس تغییر پیدا میکنند. تأثیر تغییرات جریان بر اندازه نیروهایی که سیم‌پیچی‌های ترانسفورماتور در طول پدیده فرورزونانس تحمل میکنند، موضوع مورد مطالعه این مقاله است. با شبیه‌سازی ترانسفورماتور توزیع در محیط اجزای محدود نرم‌افزار FLUX 12.2 و استفاده از کلیدزنی در شبکه، پدیده فرورزونانس مدلسازی می‌شود. با توجه به وابستگی فرورزونانس به غیرخطی بودن مشخصۀ مغناطیسی هسته آهنی ترانسفورماتور، از مدل هیسترزیس برداری Jiles–Atherton برای تولید حلقه‌های هیسترزیس هسته فولادی بهره گرفته شده است تا دقت نتایج افزایش یابد تفاصيل المقالة -
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200 - طراحی بهینه، مدلسازی و بررسی عملکرد موتور القایی تک فاز شار محوری خازن دائم با استفاده از الگوریتم بهینه سازی تجمع ذرات بهبود یافته (IPSO)
امین ابوطالبی نجف آبادیکاربرد روز افزون موتورهای القایی تکفاز شار محوری خازن دائم و بازده پایین آنها، باعث اهمیت مساله بهینه سازی این نوع موتورها گردیده است. در این مقاله، ضمن معرفی اصول الگوریتم های کلاسیک طراحی این نوع موتورها که شامل یافتن ابعاد قسمت های مختلف موتور و محاسبه پارامترهای الک أکثرکاربرد روز افزون موتورهای القایی تکفاز شار محوری خازن دائم و بازده پایین آنها، باعث اهمیت مساله بهینه سازی این نوع موتورها گردیده است. در این مقاله، ضمن معرفی اصول الگوریتم های کلاسیک طراحی این نوع موتورها که شامل یافتن ابعاد قسمت های مختلف موتور و محاسبه پارامترهای الکتریکی مانند مقاومت ها و راکتانس ها و خازن است، با معرفی مدار معادل پیشنهادی در حالت دائمی به منظور کاهش فاصله هوایی موتور، به‌معرفی ساختار الگوریتم های بهینه سازی پرداخته و در ادامه از الگوریتم های بهینه سازی ژنتیک و تجمع ذرات بهبودیافته در راستای بهینه سازی طراحی موتور شار محوری جهت افزایش بازده، افزایش ضریب توان و کاهش حجم هسته استفاده می شود. بدین منظور یک موتور القایی تک فاز شار محوری با خازن دائم که کاربرد قابل توجهی در سیستم های تهویه دارد، انتخاب شده، مورد بررسی عملکردی قرار گرفته و با استفاده از فرمول های طراحی و به‌کمک مدار معادل حالت دائمی پیشنهادی و همچنین با استفاده از روش های هوشمند نظیر الگوریتم ژنتیک و تجمع ذرات بهبودیافته، بهینه سازی موتور جهت افزایش حداکثری بازده صورت گرفته و نتایج آن در قالب نمودارهای گشتاور- سرعت و بازده- سرعت رسم و با یکدیگر مقایسه شده است. در پایان موتور طراحی شده به روش اجزای محدود جهت تایید الگوریتم طراحی، مدل حالت دائمی، الگوریتم بهینه سازی پیشنهادی و نتایج آزمایش ها شبیه سازی شده است. تفاصيل المقالة -
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201 - طراحی و تحلیل گشتاور موتور بدون جاروبک جریان مستقیم شیار دوبل با آهنرباهای اسپکی و سطحی با استفاده از روش اجزاء محدود
علی استکی بهروز مجیدیهدف از این تحقیق، مطالعه تأثیر شیار دوم در دندانه استاتور بر روی عملکرد دو ساختار متداول روتور به نام های اسپکی و سطحی، برای موتور جریان مستقیم بدون جاروبک (BLDC) است. نتایج برای حالت های مختلف بسته بودن شیارها ارائه و مقایسه شده است. سپس با جای گذاری یک سیم پیچ تغذیه ش أکثرهدف از این تحقیق، مطالعه تأثیر شیار دوم در دندانه استاتور بر روی عملکرد دو ساختار متداول روتور به نام های اسپکی و سطحی، برای موتور جریان مستقیم بدون جاروبک (BLDC) است. نتایج برای حالت های مختلف بسته بودن شیارها ارائه و مقایسه شده است. سپس با جای گذاری یک سیم پیچ تغذیه شده با جریان مستقیم و یا آهنرباهای مغناطیس دائم درون شیار دندانه های استاتور موتوری که در مراحل قبل بهترین عملکرد را داشته، دو مدل هیبرید BLDC معرفی و مورد مطالعه قرار گرفته اند. نتایج حاکی از آن است که رویکرد بستن شیار به شدت بر روی نوسانات گشتاور مؤثر است در حالی که گشتاور تولیدی هر دو ساختار تقریباً ثابت مانده است. در خصوص HBLDC، میدان الکترومغناطیسی جانبی که در شیار دندانه استاتور جای گذاری شده عملکرد گشتاوری موتورها را بهبود می بخشد. در همه مراحل این تحقیق از روش اجزای محدود استفاده شده است. تفاصيل المقالة -
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202 - طراحی موتور سوئیچ رلوکتانس القایی پیشران برای اتوبوس برقی
علی مدنی محمدی محمدعلی عباسیان مجید دلشاد هادی ثقفیدر سال های اخیر، کلان شهرها در سراسر جهان شاهد روند کاهشی در شاخص کیفیت هوا بوده‌اند. بخش زیادی از این آلودگی مربوط به وسایل حمل و نقل عمومی است. ارتقای حمل و نقل عمومی می تواند راه کاری برای خروج از این بن بست باشد. به دلیل نگرانی های زیست محیطی، توصیه می شود به تغییر أکثردر سال های اخیر، کلان شهرها در سراسر جهان شاهد روند کاهشی در شاخص کیفیت هوا بوده‌اند. بخش زیادی از این آلودگی مربوط به وسایل حمل و نقل عمومی است. ارتقای حمل و نقل عمومی می تواند راه کاری برای خروج از این بن بست باشد. به دلیل نگرانی های زیست محیطی، توصیه می شود به تغییر اتوبوس‌های دیزلی معمولی به اتوبوس‌های برقی، که دارای مزایای متعددی از نظر کاهش آلودگی، صدا و سوخت هستند. در این مقاله یک موتور سوئیچ رلوکتانس القایی توان بالا که در اتوبوس برقی استفاده می شود مورد مطالعه قرار گرفته است. ساختار استاتور و روتور این ماشین الکتریکی غیر سگمنتال است. ساختار به گونه ای است که مسیر شار مغناطیسی کوتاه در روتور و هسته استاتور ایجاد شده است. در نتیجه گشتاور بالا با تلفات کم تولید می شود. از آنجایی که موتور الکتریکی مورد استفاده برای اتوبوس برقی دارای توان بسیار بالا است، در نتیجه نیاز به مقدار زیادی آهنربای دائم دارد. لذا مطلوب است که موتور الکتریکی برای اتوبوس برقی فاقد آهنربای دائم باشد. در این مطالعه یک موتور سوئیچ رلوکتانس القایی سه فاز با توان ۲۲۰ کیلووات، با ۶ قطب استاتور و ۴ قطب روتور در نظر گرفته شده است. یک مدل المان محدود دو بعدی طراحی شده و تجزیه و تحلیل مغناطیسی آن انجام می‌گیرد. مسیر شار، گشتاور و بازده موتور سوئیچ رلوکتانس القایی محاسبه شده و نتایج ارائه شده است. تفاصيل المقالة -
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203 - ارزیابی شبکه‌های عصبی انعطاف‌پذیر باساختار قابل بازسازی در حین آموزش جهت تخمین هارمونیکهای جریان استاتور ژنراتور آسک نیروگاه ری بر اساس الگوریتم CFE/SS
محمدرضا یوسفی محمد تشنه لبیکی از روشهای تشخیص خطای ژنراتور در حین کار، آنالیز هارمونیکهای جریان استاتور میباشد. در این مقاله از شبکه‌های عصبی انعطاف‌پذیر با قابلیت بازسازی خود در حین آموزش برای تعیین هارمونیکهای جریان استاتور ژنراتور، در بارهای مختلف استفاده شده است. داده‌های آموزش دهندة شبکه ع أکثریکی از روشهای تشخیص خطای ژنراتور در حین کار، آنالیز هارمونیکهای جریان استاتور میباشد. در این مقاله از شبکه‌های عصبی انعطاف‌پذیر با قابلیت بازسازی خود در حین آموزش برای تعیین هارمونیکهای جریان استاتور ژنراتور، در بارهای مختلف استفاده شده است. داده‌های آموزش دهندة شبکه عصبی با استفاده از مدل سازی ژنراتور و استفاده از روش المان محدود (FE) و فضای حالت (SS)، در نقاط مختلف بار روی منحنی بهره برداری ژنراتور برای سه سطح مختلف ولتاژ پایانه به دست آمده است. شبکة عصبی که با استفاده از این داده‌ها آموزش داده شده است، یک شبکة پرسپترون با یک لایة پنهان و با قانون یادگیری پس انتشار خطا میباشد. نتایج نشان می‌دهد که شبکه عصبی انعطاف‌پذیر آموزش داده شده با خطای کمتر از ده درصد میتواند هارمونیکهای جریان را برای نقاط بار دلخواه روی منحنی بهره‌برداری، نسبت به نتایج حاصل از الگوریتم CFE-SS به دست آورد. پارامترهای نامی ژنراتور آسک عبارتند از: 43950 کیلو ولت آمپر، 11 کیلو ولت، 3000 رادیان بر دقیقه، 50 هرتز و ضریب توان 0.8. تفاصيل المقالة -
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204 - مدلسازی سیستم تعلیق الکترودینامیکی نوع آهنربای دائم با لحاظ کردن اثر پوستی
محمد رجبی سبدانی عباس نجارخدابخش احمد دارابیدر این مقاله ایجاد نیروهای معلق مغناطیسی و مقاوم رانش در سیستم تعلیق الکترودینامیکی با استفاده از آهنربای دائم مورد بررسی قرار گرفته است. سیستم تعلیق الکترودینامیکی نیروی عکس العمل متقابل دو میدان مغناطیسی است که براساس خاصیت دفعی تولید شده و باعث ایجاد تعلیق می‌شود. بخ أکثردر این مقاله ایجاد نیروهای معلق مغناطیسی و مقاوم رانش در سیستم تعلیق الکترودینامیکی با استفاده از آهنربای دائم مورد بررسی قرار گرفته است. سیستم تعلیق الکترودینامیکی نیروی عکس العمل متقابل دو میدان مغناطیسی است که براساس خاصیت دفعی تولید شده و باعث ایجاد تعلیق می‌شود. بخش معلق این سیستم شامل یک آهنربای دائم مکعبی شکل و مسیر راهنمای آن یک ریل آلومینیومی با ضخامت دو میلیمتر است که در مدل تحلیلی آهنربا با مدل ورقهای جریان مدل شده است و جریان القایی ناشی از تغییر میدان در ریل آلومینیومی با لحاظ کردن اثر پوستی محاسبه شده است. جهت بررسی اثر پوستی، ریل آلومینیومی چند لایه با هدایت الکتریکی متفاوت فرض شده است. نیروهای تعلیق و مقاوم رانش در سرعتهای مختلف به کمک مدل تحلیل محاسبه شده‌اند. سپس به کمک روش اجزای محدود دوبعدی سیستم مدلسازی شده و تأثیر تغییر سرعت بر نیروهای تعلیق و مقاوم رانش در دو فاصله هوایی مختلف مورد بررسی قرار گرفته است. نتایج شبیه‌سازی شده توسط مدل تحلیلی با روش اجزای محدود مقایسه شده و مورد تأیید قرار گرفته است تفاصيل المقالة -
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205 - روشی جدید برای تشخیص عیب ناهم راستایی استاتیک در موتورهای القایی قفس سنجابی
مهدی احمدی جواد پشتان سید مهدی میر ایمانیدر این مقاله به تشخیص عیب ناهم‌راستایی استاتیک در موتورهای القایی قفس سنجابی پرداخته می‌شود. برای مدلسازی موتور القایی در حالت سالم و معیوب از روش اجزاء محدود دو بعدی استفاده شده است و اعتبارسنجی روش ارائه شده با مقایسه سیگنال‌های جریان و سرعت شبیه سازی شده در حالت سال أکثردر این مقاله به تشخیص عیب ناهم‌راستایی استاتیک در موتورهای القایی قفس سنجابی پرداخته می‌شود. برای مدلسازی موتور القایی در حالت سالم و معیوب از روش اجزاء محدود دو بعدی استفاده شده است و اعتبارسنجی روش ارائه شده با مقایسه سیگنال‌های جریان و سرعت شبیه سازی شده در حالت سالم با داده‌های عملی انجام شده است. برای تشخیص عیب در ابتدا از روش تبدیل فوریه سریع سیگنال جریان استفاده می‌شود. اگرچه نتایج حاصل از این روش، وقوع عیب را هشدار میدهند اما برای تحلیل لازم است از هارمونیکهای مرتبه بالا استفاده شود و به‌دلیل دامنه کوچک این هارمونیک‌ها، مقایسه بسیار مشکل خواهد بود. برای رفع این مشکلات پیشنهاد می‌شود از دو سیم‌پیچ آزمایش متقارن در اطراف فاصله هوایی استفاده شود تا هرگونه تغییر در این ناحیه بتواند به خوبی قابل تشخیص باشد. به خاطر استفاده سیم‌پیچ‌ها در حالت مدار باز، این سیم‌پیچ‌ها بر دینامیک موتور تأثیری نمی‌گذارند و از طرفی نتایج نشان میدهند که تحلیل ولتاژ القا شده در آنها میتواند وقوع عیب، نوع و درصد آن را به‌خوبی نشان دهد. تفاصيل المقالة -
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206 - بررسی عددی اثر مانع دیواری شامل گویهایECO-LINE بر انحراف مسیرگسلش 45 درجه شیب لغز معکوس
نیما آجلی لاهیجی بهنام ادهمی غلامرضا قدرتی امیری الهام رجبیگسلش ناشی از زلزله به‌صورت گسیختگی از لایه‌های زمین و خاک عبور کرده و به سطح زمین می‌رسد و باعث آسیب به سازه‌های زیرساختی به‌ویژه پل‌ها میگردد، بدین منظور انحراف مسیر گسیختگی خاک در مجاورت سازه با روشهای نوین حائز اهمیت است. حفر مانع دیواری در مسیر انتشار گسیختگی و در أکثرگسلش ناشی از زلزله به‌صورت گسیختگی از لایه‌های زمین و خاک عبور کرده و به سطح زمین می‌رسد و باعث آسیب به سازه‌های زیرساختی به‌ویژه پل‌ها میگردد، بدین منظور انحراف مسیر گسیختگی خاک در مجاورت سازه با روشهای نوین حائز اهمیت است. حفر مانع دیواری در مسیر انتشار گسیختگی و در مجاورت سازه به‌عنوان یکی از راهکارهای مؤثر کاهش اثرات ثانویه (جابجایی سطح زمین، دوران فونداسیون و پایه‌های سازه) ناشی از این پدیده است. در این مقاله مطالعه و بررسی عددی یک مانع دیواری پرشده با گویهای Eco-Line در مجاورت فونداسیون یک پل بتنی به‌عنوان روشی جدید جهت انحراف مسیر گسلش ارائه گردید و تأثیر پارامترهای مختلف ازجمله تغییرات عرض، عمق و فاصله مانع دیواری از فونداسیون پل بر انحراف مسیر، گسل 45 درجه شیب‌لغز معکوس و تغییرات جابجایی قائم و دوران فونداسیون موردبررسی قرار گرفت. نتایج نشان داد، هنگامی‌که فاصله مانع دیواری تا پایه پل و همچنین عمق مانع به نحوی باشد که در مسیر انتشار امواج گسلش قرار گیرد به نحو مطلوبی امواج منحرف و کرنش پلاستیک، انرژی کرنش خاک و تغییر شکل سطح زمین تا 100 درصد و پاسخ سازه حداکثر تا 50 درصد کاهش می‌یابد و از آسیب به سطح زمین و سازه جلوگیری می‌کند. تفاصيل المقالة -
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207 - بررسی عددی اتصال پیشنهادی فلزی با استفاده از استاب ستون کوتاه
فرزاد حاتمی برق مهرداد طاهری پور رضا رئوفیدر سازه‌های آسیب دیده در زلزله‌های مختلف، تنها شواهد اندکی دال بر اینکه نواحی پلاستیک واقعاً تشکیل شده باشند وجود دارد. اکثر مطالعات انجام شده بر روی ایجاد مفصل پلاستیک در قسمتی از تیر تمرکز داشته، که این امر در صورت وقوع باعث آسیب غیر قابل جبران برای تیر می‌شود و أکثردر سازه‌های آسیب دیده در زلزله‌های مختلف، تنها شواهد اندکی دال بر اینکه نواحی پلاستیک واقعاً تشکیل شده باشند وجود دارد. اکثر مطالعات انجام شده بر روی ایجاد مفصل پلاستیک در قسمتی از تیر تمرکز داشته، که این امر در صورت وقوع باعث آسیب غیر قابل جبران برای تیر می‌شود و در صورت عدم وقوع مفصل پلاستیک در تیر سبب انتقال نیرویی بیش از لنگر پلاستیک تیر به اتصال و در نتیجه به ستون شده که این امر یا باعث شکست ترد اتصال می‌شود و یا منجر به آسیب دیدن ستون به ویژه چشمه اتصال خواهد شد. لذا در این تحقیق با هدف کاهش آسیب در تیر و ستون و امکان جایگزینی قطعات آسیب چهار اتصال با هندسه جدید ارائه شده است. در حالت کلی، اتصالات پیشنهادی با جایگزینی یک مقطع H یاI شکل همراه یا به‌جای ورق‌انتهایی به عنوان استاب ستون کوتاه پیشنهاد میگردد. در این مطالعه ابتدا یک نمونه مدل اجزاء محدودی از اتصال ورق انتهایی که ترکیب جوش و پیچ بوده و تحت بار گذاری متناوب قرار گرفته است، انتخاب و پس از صحت سنجی در نرم‌افزار آباکوس مطالعه برروی اتصالات پیشنهادی انجام پذیرفت. نتایج نشان می‌دهد ناحیه‌ی استاب، با رفتار غیرخطی، یک مفصل محدود کنترل شده، با شکلپذیری فوق العاده را بوجود می‌آورد. تسلیم به هنگام در استاب سبب رفتار فیوزی آن و عدم آسیب به تیر و ستون می‌شود و تنش و کرنش پلاستیک را به‌طور‌قابل ملاحضه‌ایی در چشمه اتصال ستون کاهش می‌دهد. تفاصيل المقالة -
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208 - پیشبینی پارامترهای چسبندگی الیاف فولادی هوک شکل و بتن با استفاده از شبکه‌های عصبی مصنوعی
امیر ابراهیم اکبری بقال امیر ابراهیم اکبری بقالبا توجه به اهمیت بکارگیری الیاف فولادی در تقویت بتن، در تحقیق حاضر با استفاده از شبکه‌های عصبی مصنوعی به پیشبینی رفتار بیرون کشیدگی الیاف فولادی هوک شکل از بتن پرداخته شده است. به دلیل محدودیت داده‌های جامع آزمایشگاهی، از داده‌های به دست آمده از تحلیل المان محدود به عن أکثربا توجه به اهمیت بکارگیری الیاف فولادی در تقویت بتن، در تحقیق حاضر با استفاده از شبکه‌های عصبی مصنوعی به پیشبینی رفتار بیرون کشیدگی الیاف فولادی هوک شکل از بتن پرداخته شده است. به دلیل محدودیت داده‌های جامع آزمایشگاهی، از داده‌های به دست آمده از تحلیل المان محدود به عنوان ورودی شبکه عصبی استفاده شده است. به منظور شبیه‌سازی بیرون کشیدگی الیاف از روش المان محدود سه‌بعدی و نرم‌افزار آباکوس استفاده می‌شود. در مدل المان محدود، اندرکنش بین الیاف و بتن با استفاده از مفهوم ناحیه انتقالی سطح مشترک شبیه‌سازی شده است که پارامترهای آن با استفاده از روش المان محدود معکوس و استفاده از نتایج تست تجربی بیرون‌کشیدگی انجام پذیرفته بر روی یک نمونه الیاف به دست آمده است. پس از صحت‌سنجی نتایج مدل عددی با نتایج تجربی، نتایج به ازای پارامترهای مؤثر الیاف استخراج شده و بر اساس آنها مدلسازی با استفاده از شبکه‌های عصبی صورت گرفته است. پیشبینی نیروی بیرون‌کشیدگی توسط شبکه‌های عصبی مصنوعی چندلایه و الگوریتم آموزش انتشار به عقب، با تکنیک بهینه‌سازی مارکورادت-لونبرگ انجام شده است. نتایج نشان می‌دهد که مدل شبکه عصبی ارائه شده در این تحقیق، به دلیل توانای استفاده از متغیرهای بیشتر در مدلسازی و نتایج دقیق‌تر، روشی مؤثر برای پیشبینی نیروی بیرون‌کشیدگی الیاف از بتن است. تفاصيل المقالة -
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209 - بررسی کارایی روش اصلاح شده‌ی بی ‏نیاز از المان گالرکین در حل مسائل استاتیکی و بهسازی
رامین وفائی پور علی زارع علیرضا علیزاده مجدی فریبا بهروز سرندروش رایج المان محدود روشی قدرتمند در حل مسائل مقدار مرزی است که معادلات فرم قوی دیفرانسیلی را با استفاده از گسسته‌سازی دامنه به معادلات فرم ضعیف تبدیل می کند. این روش اگرچه برای محاسبه ی تغییر مکان (متغیر مکانی) در حل مسائل استاتیکی و دینامیکی به خوبی کاراست اما در محاس أکثرروش رایج المان محدود روشی قدرتمند در حل مسائل مقدار مرزی است که معادلات فرم قوی دیفرانسیلی را با استفاده از گسسته‌سازی دامنه به معادلات فرم ضعیف تبدیل می کند. این روش اگرچه برای محاسبه ی تغییر مکان (متغیر مکانی) در حل مسائل استاتیکی و دینامیکی به خوبی کاراست اما در محاسبه ی مقادیر تنش دچار مقداری خطا می‌شود. برای رفع این خطا که ناشی از گسسته بودن میدان تنش محاسباتی است و همچنین برای رفع مشکل نیازمندی به شبکه مش از پیش تعریف شده برای گسسته سازی دامنه، روش های بی نیاز از المان (مش) شکل گرفته اند. یکی از این روش ها، روش بی نیاز از المان گالرکین می باشد. توابع شکل ایجادی در روش بی نیاز از المان گالرکین مبتنی بر تقریب کمترین مربعات متحرک می باشند. این توابع شکل دارای خاصیت درون یابی نبوده و خاصیت دلتای کرونیکر را ندارند. اخیرا روشی توسط محققین برای ایجاد خاصیت درون یابی در توابع شکل کمترین مربعات متحرک برای حل مسائلی با گسسته سازی مرز دامنه ارائه گردیده است. تاکنون ارزیابی از عملکرد روش اصلاحی پیشنهاد شده در حل مسائل مرتبط با کل دامنه ارائه نگشته است. در این مقاله با استفاده از روش مورد اشاره، روش بی نیاز از المان گالرکین اصلاح گردیده و برای حل مسائل با گسسته سازی کل دامنه به کار گرفته شده است. کاربرد و کارآیی روش اصلاحی مورد استفاده در حل مسائل استاتیکی در این مقاله مورد ارزیابی قرار گرفته است و مقایسه‌ای میان عملکرد روش اولیه و روش اصلاح شده ارائه گردیده است. تفاصيل المقالة -
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210 - بررسی رفتار ستون‌های فولادی دو جداره پر شده با بتن (CFDST) تحت بارگذاری پیچشی چرخه‌ای
احمد ملکی رضا خلیلیستون های فولادی دوجداره پر شده با بتن (Concrete- Filled Double Skin Steel Tubular) جزء خانواده ی ستون های فولادی پر شده با بتن(CFST) به شمار می روند، در ستون های CFDST جداره فولادی و بتن موجود بر رفتار یکدیگر تأثیرگذارند، به نحوی که بتن مانع از کمانش جداره های فولادی دا أکثرستون های فولادی دوجداره پر شده با بتن (Concrete- Filled Double Skin Steel Tubular) جزء خانواده ی ستون های فولادی پر شده با بتن(CFST) به شمار می روند، در ستون های CFDST جداره فولادی و بتن موجود بر رفتار یکدیگر تأثیرگذارند، به نحوی که بتن مانع از کمانش جداره های فولادی داخلی و بیرونی می شود و دو جداره فولادی تحت اثر بارگذاری موجب ایجاد نیروی دورگیر(Confinement Force) می گردد و از همین رو موجب افزایش شکل پذیری و مانع از ترد شکنندگی بتن می گردد. برای اطمینان از درستی مدل سازی در نرم افزار عناصر محدود، نتایج آزمایشگاهی با نتایج عناصر محدود مقایسه، و از صحت و درستی مدل سازی اطمینان حاصل گردیده است. در این مقاله به بررسی مشخصات هندسه مقطع، تحت بارگذاری مونوتونیک و بارگذاری چرخه ای پرداخته شده، که نتایج حاصل از این تحقیق نشان می دهد ستون های CFDST دارای شکل پذیری بالا، جذب انرژی بیشتر در زلزله، بهبود رفتار ستون های CFDST تحت بارگذاری رفت و برگشتی و همچنین کاهش وزن ستون در مقایسه با ستون های CFST اشاره کرد تفاصيل المقالة -
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211 - معرفی و مدلسازی عددی نوعی پانل پیش‌ساخته کامپوزیت مسلح به‌عنوان یک تکنولوژی نوین در صنعت ساختمان
مهرداد موحدنیا محمد رضا تابش پوربا توجه به بررسی های انجام شده استفاده از مصالح ضعیف و شکننده ای مانند آجر سنتی به علت وزن زیاد، مقاومت و شکلپذیری پایین در اثر وقوع زلزله با بیشترین خسارات و تلفات جانی همراه خواهند بود. در مقاله حاضر رفتار نوعی پانل مسلح کامپوزیت نوین در ساختمان مورد مطالعه و مزایای أکثربا توجه به بررسی های انجام شده استفاده از مصالح ضعیف و شکننده ای مانند آجر سنتی به علت وزن زیاد، مقاومت و شکلپذیری پایین در اثر وقوع زلزله با بیشترین خسارات و تلفات جانی همراه خواهند بود. در مقاله حاضر رفتار نوعی پانل مسلح کامپوزیت نوین در ساختمان مورد مطالعه و مزایای آن در مقایسه با مصالح سنتی بکار رفته در ساختمان های معمول مورد ارزیابی قرار گرفته شده است. مواد کامپوزیت قابل دسترس و ارزان قیمت استفاده شده در این پانل علاوه بر افزایش مقاومت فشاری و کششی باعث یکپارچگی این قطعات شده به نحوی که در هنگام خرابی، ذرات آن متلاشی نشده و هیچگونه آواری نخواهد داشت. به منظور دستیابی به مشخصات مکانیکی و رفتاری این محصول نوین آزمایشات متعدد کششی، فشاری و برشی روی نمونه های مختلف در آزمایشگاه مصالح دانشکده مکانیک دانشگاه صنعتی شریف انجام شده است. شکلپذیری، مقاومت کششی و فشاری بسیار خوب، وزن پایین، حداقل هزینه و زمان در اجرا، افزایش جذب انرژی و... از مزایای این محصول نوین در مقایسه با مصالح بنایی موجود میباشد. در ادامه به منظور بررسی دقیق رفتار پانل‌های گچی مرکب به عنوان دیوارهای باربر و نیز مقایسه‌ی رفتار لرزهای آنها با رفتار دیوار بنایی متناظر با بازشو ، به مدلسازی و تحلیل چندین دیوار با بازشو با نرم‌افزار اجزای محدود پرداخته شده است. نتایج آزمایشات انجام شده نشان داد که مقاومت کششی و فشاری این پانل به ترتیب 3/4 و 18 کیلوگرم بر سانتی‌متر مربع بوده که در مقایسه با مصالح بنایی مورد استفاده دیگر قابل ملاحظه میباشد. تفاصيل المقالة -
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212 - برش پانچینگ در دالهای تخت و راهکار مناسب جهت جلوگیری از شکست برشی در دال‌ها
جواد عزتی ارسطو ارمغانیچکیده رفتار دال بتن مسلح در محل اتصال به ستون بتنی به دلیل احتمال ایجاد شکست برشی در این قسمت یکی از مهم ترین دغدغه های مهندسین در طراحی این اعضا می باشد. با وجود تحقیقات گسترده و بهبود چشمگیر استانداردهای مرتبط، نگرانی هایی در مورد ارزیابی سیستم های دال تخت وجود دارد. أکثرچکیده رفتار دال بتن مسلح در محل اتصال به ستون بتنی به دلیل احتمال ایجاد شکست برشی در این قسمت یکی از مهم ترین دغدغه های مهندسین در طراحی این اعضا می باشد. با وجود تحقیقات گسترده و بهبود چشمگیر استانداردهای مرتبط، نگرانی هایی در مورد ارزیابی سیستم های دال تخت وجود دارد. در این مقاله بررسی برش پانچینگ در دال های تخت مورد مطالعه قرار گرفته و سعی شده است با روشهای مناسب از جمله استفاده از پهنه، گل‌میخ های فولادی با شکست برشی در محل اتصال به ستون مقابله گردد. لازم به ذکر است با روش اجزای محدود و در نرم افزار المان محدود Ansys این مطالعه انجام پذیرفته و در نهایت با ارائه نتایج شبیه‌سازی های عددی، تاثیر نتایج به دست آمده بررسی و ارزیابی شده است. تفاصيل المقالة -
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213 - مطالعه عددی تأثیر دال بتن آرمه فداشونده بر عملکرد سازه‌های بتن‌آرمه قوسی شکل زیرزمینی تحت بار انفجار
سید صفر صالح کوتاه اسماعیل ایزدی زمان آبادیبا گسترش روزافزون تکنولوژی ساخت تجهیزات نظامی با تخریب بالا، نیاز به ساخت سازه‌هایی با مقاومت قابل قبول در برابر انفجار در مراکز حساس و حیاتی بیش از پیش احساس می‌شود. این سازه‌ها به عنوان امکانات شهری در زمان صلح و در زمان جنگ و بلایای طبیعی عاملی برای حفظ جان مردم محسو أکثربا گسترش روزافزون تکنولوژی ساخت تجهیزات نظامی با تخریب بالا، نیاز به ساخت سازه‌هایی با مقاومت قابل قبول در برابر انفجار در مراکز حساس و حیاتی بیش از پیش احساس می‌شود. این سازه‌ها به عنوان امکانات شهری در زمان صلح و در زمان جنگ و بلایای طبیعی عاملی برای حفظ جان مردم محسوب می‌شوند. به علت عدم وجود اطلاعات تجربی مناسب و مشکلات روشهای آزمایشگاهی در زمینه انفجار سازه‌ها، استفاده از روشهای مدلسازی عددی و اجزا محدود میتواند کمک شایانی در طراحی سازه‌ها و برآورد بارهای وارد بر آنها داشته باشد. در این تحقیق تأثیر دال بتن‌آرمه فداشونده بر عملکرد سازه‌های بتن‌آرمه قوسی شکل زیرزمینی تحت بار انفجار با جزئیات متداول و همچنین پارامترهای تأثیرگذار مختلف مورد مطالعه قرار گرفته است. جهت حل از نرم‌افزار اجزا محدود Ls-Dyna استفاده شده و مدلهای بهینه‌سازی شده قوس‌های بتنی تحت میزان مختلف مواد منفجره مورد بررسی قرار گرفته است. نتایج تحلیل‌های مختلف صورت گرفته نشان می‌دهد که در صورت قرار دادن دال بتنی فداشونده روی تاج سازه قوسی شکل زیرزمینی تخریبی روی سازه مورد مطالعه صورت نمی‌گیرد و فقط تخریب مربوط به دال بتنی خواهد بود که با افزایش میزان TNT تخریب روی آن بیشتر می‌شود و در اصل وجود این دال باعث پخش قدرت انفجار در سطح بیشتری از خاک میگردد که این موجب کاهش انتقال نیرو به سازه مورد مطالعه میباشد. بنابراین درجه ایمنی این سازه‌ها به لحاظ عملکرد در برابر بار انفجار به میزان قابل توجهی افزایش خواهد یافت. تفاصيل المقالة -
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214 - بررسی مقاومت خمشی بتن فوق‌توانمند تقویت شده با الیاف فولادی با استفاده از مدل المان محدود چندمقیاسه
امیر ابراهیم اکبری بقال احمد ملکی رامین وفائی پورهدف اصلی تحقیق حاضر، توسعه مدل المان محدود به منظور مطالعه تأثیر الیاف فولادی شکل بر مقاومت خمشی بتن فوق توانمند الیافی است. بدین منظور، به منظور شبیه‌سازی عددی، مدل المان محدود چندمقیاسه توسعه داده شد که در آن بتن به صورت ماده همگن و یکنواخت مدلسازی شده و الیاف فولادی أکثرهدف اصلی تحقیق حاضر، توسعه مدل المان محدود به منظور مطالعه تأثیر الیاف فولادی شکل بر مقاومت خمشی بتن فوق توانمند الیافی است. بدین منظور، به منظور شبیه‌سازی عددی، مدل المان محدود چندمقیاسه توسعه داده شد که در آن بتن به صورت ماده همگن و یکنواخت مدلسازی شده و الیاف فولادی به صورت تصادفی در داخل آن توزیع شده است. به منظور در نظر گرفتن فرضیات واقع‌بینانه‌تر، ناحیه چسبندگی بین الیاف و بتن نیز لحاظ شده است. پس از صحت‌سنجی نتایج مدل المان محدود با نتایج تستهای تجربی، تأثیر پارامترهای مانند کسر حجمی و چسبندگی الیاف فولادی بر استحکام مشخصه‌های مقاومت خمشی بتن‌های فوق توانمند تقویت شده با الیاف مورد مطالعه عددی قرار گرفته است. نتایج نشان می‌دهد که تأثیر استفاده از الیاف بر میزان جذب انرژی توسط بتن فوق توانمند الیافی بسیار بیشتر از تأثیر آن بر سایر مشخصه‌های این نوع بتن‌ها میباشد و مخصوصاً استفاده از الیاف در حجم‌های پایین الیاف، تأثیری بسیار قابل ملاحظه بر قابلیت جذب انرژی دارد به طوری که به ازای 5/0 درصد کسر حجمی الیاف فولادی در حدود 17 برابر نسبت به نمونه بتن فوق توانمند بدون الیاف افزایش می‌یابد. تفاصيل المقالة -
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215 - بررسی عوامل موثر جهت رفع نقص کاهش محصورشدگی بتن هسته در ستون‌های CFT با مقطع نامتقارن L شکل توسط تحلیل عددی اجزاء محدود
سید علی موسوی داودی مرتضی نقی پوراستفاده از ستون های فولادی پرشده با بتنCFT بعلت همکاری توام مناسب بتن و فولاد در سرتاسر جهان رو به افزایش است، ستون های فولادی پرشده با بتن بیشتر در اشکال دایره ا ی اجرا می شود، دلیل این موضوع این نکته است که مقطع دایره ا ی محصور شدگی بیشتری را برای بتن هسته ایجاد می کن أکثراستفاده از ستون های فولادی پرشده با بتنCFT بعلت همکاری توام مناسب بتن و فولاد در سرتاسر جهان رو به افزایش است، ستون های فولادی پرشده با بتن بیشتر در اشکال دایره ا ی اجرا می شود، دلیل این موضوع این نکته است که مقطع دایره ا ی محصور شدگی بیشتری را برای بتن هسته ایجاد می کند، اما در بعضی از مواقع استفاده از مقطع متقارن همیشه امکان پذیر نیست و اشکال دیگر همچون مقطع L شکل استفاده می گردد، این مقاطع به دلیل نامتقارن بودن محصور شدگی کمتری را برای بتن هسته ایجاد می نمایند، این امر سبب کاهش ظرفیت باربری بر روی این ستون ها با مقطع نامتقارن L شکل می گردد. با توجه به این مهم در این پژوهش به مطالعه ستون های فولادی پرشده با بتن با مقطع نامتقارن L شکل در جهت تامین رفع کاهش محصور شدگی تحت اثر پارامترهای موثر از جمله ارتفاع ، ضخامت مقطع فولادی و تنش فشاری بتن پرداخته شد، بعد از انجام بررسی اثر تاثیر پارامترهای ارتفاع، ضخامت جدار فولادی و مقاومت فشاری بتن بر روی اثر تامین محصور شدگی بتن هسته در مقاطع L شکل تحت تحلیل اجزای محدود مشاهده گردید که اثر ضخامت جدار فولادی (t) در مقاطع L شکل از تاثیر گذارترین پارامترها در جهت رفع نقص کاهش محصور شدگی است، که اثر این تاثیر گذاری به طور میانگین چیزی در حدود 31/18 درصد بیشتر از پارامترهای مطالعاتی مقاومت فشاری بتن و ارتفاع بود، در انتها نتیجه‌گیری شد که در مقاطع نامتقارن L شکل با تغییر ضخامت جدار فولادی نسبت به پارامتر مقاومت فشاری بتن و ارتفاع، محصور شدگی بیشتری برای مقاطع نامتقارن L شکل تامین خواهد شد. تفاصيل المقالة -
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216 - ارزیابی عملکرد لرزهای سازه‌های فولادی مجهز به مهاربندهای ترکیبی فولاد-آلیاژ حافظه‌دار شکلی
محمد هوشمند بهزاد رافضی جلیل خلیل علافیدر این مقاله به بررسی رفتار لرزهای مهاربندهای ترکیبی از جنس فولاد و آلیاژهای حافظه‌دار شکلی پرداخته شده است. جهت بررسی از شش مدل مهاربند ترکیبی با میزان مصرف آلیاژ حافظه‌دار شکلی با معیار طول به ترتیب صفر ، 20 ، 40 ، 60 ، 80 و 100 درصد از طول کل استفاده شده است. ارزیاب أکثردر این مقاله به بررسی رفتار لرزهای مهاربندهای ترکیبی از جنس فولاد و آلیاژهای حافظه‌دار شکلی پرداخته شده است. جهت بررسی از شش مدل مهاربند ترکیبی با میزان مصرف آلیاژ حافظه‌دار شکلی با معیار طول به ترتیب صفر ، 20 ، 40 ، 60 ، 80 و 100 درصد از طول کل استفاده شده است. ارزیابی مدل‌ها به کمک تحلیل دینامیکی غیر خطی تحت زلزله السنترو مقیاس شده با شتاب‌های حداکثر 0.6g و 0.9g در نرم افزار ANSYS v11 انجام گرفته است. نتایج مطالعات انجام شده مقادیر طولی بهینه برای درصد مهاربند ترکیبی را مشخص می‌کند بطوریکه میتوان با استفاده از مقادیر پیشنهادی و طرح ارائه شده، سازه‌هایی بار رفتار لرزهای مناسب و با هزینه ساخت قابل توجیه طراحی و اجرا نمود. تفاصيل المقالة -
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217 - مطالعه رفتار مکانیکی ستون‌های مرکب فولادی پرشده با بتن با سطح مقطع (T) شکل تحت تحلیل حساسیت عددی اجزای محدود تحت بار محوری
سید علی موسوی داودی مرتضی نقی پورستون های فولادی پر شده با بتن (CFT) Concrete Filled Tube در سالیان اخیر به علت مزایای فراوان خود در ساختمان های بلند و صنعتی، پل ها، اسکله ها و نیز شمع ها رواج زیادی پیدا کرده است. این ستونها اغلب بیشتر در اشکال دایره‌ای اجرا میگردد. دلیل اصلی این موضوع این نکته هست ک أکثرستون های فولادی پر شده با بتن (CFT) Concrete Filled Tube در سالیان اخیر به علت مزایای فراوان خود در ساختمان های بلند و صنعتی، پل ها، اسکله ها و نیز شمع ها رواج زیادی پیدا کرده است. این ستونها اغلب بیشتر در اشکال دایره‌ای اجرا میگردد. دلیل اصلی این موضوع این نکته هست که مقاطع دایره‌ای محصور شدگی بیشتری را نسبت به مقاطع دیگر در بتن هسته ایجاد می‌کند. این مهم سبب گردیده که مقاطع دایره‌ایی نسبت به مقاطع دیگر در ستون‌های CFT بیشتر مورد استفاده قرار گیرد. اما در بعضی از مواقع استفاده از مقاطع دایره‌ای غیر ممکن خواهد شد و مجبور به استفاده از اشکال خاص از جمله مقاطع مربع و مسطیل و مقاطع با اشکال L و T شکل در بعضی از قسمتهای ساختمانی مورد استفاده قرار گیرد. با توجه به اهمیت این موضوع در این مقاله سعی گردید که به معرفی و بررسی رفتار مکانیکی ستون‌های CFT با مقطع هندسی T شکل و بررسی اثر پارامتری ضخامت جدار فولاد، و تنش فشاری بتن، بر روی ظرفیت و رفتار مکانیکی این ستونها پرداخته شود، در انتها بعد از انجام پژوهش مشخص گردید، در ستون‌های CFT با مقطع هندسی T شکل، بین اثر ضخامت جدار فولادی و نوع بتن، پارامتر ضخامت جدار فولادی پارامتر تاثیرگذارتری بر روی ظرفیت باربری ستون‌های CFT است، همچنین بین پارامتر ضخامت جدار فولادی و ارتفاع مقطع، تاثیر تغییرات ارتفاع بر روی شکلپذیری و سختی و ظرفیت باربری مقطع به طور میانگین بیشتر از پارامتر ضخامت جدار فولادی است. تفاصيل المقالة -
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218 - ارزیابی عددی و آزمایشگاهی دیوار برشی فولادی با بازشوهای دایره‌ای تحت بار چرخه‌ای
علی صاحب جمع حسین شوکتیچکیده سیستم دیوار برشی فولادی یک سیستم باربر جانبی است که به سبب داشتن مزایایی از جمله شکلپذیری مناسب، سختی زیاد، میزان مقاومت برشی و جذب انرژی بالا همواره مورد توجه محققین بوده است. از سال 1980 میلادی که تحقیقات پایه برروی دیوار برشی فولادی بدون سخت‌کننده صورت پذیرفت أکثرچکیده سیستم دیوار برشی فولادی یک سیستم باربر جانبی است که به سبب داشتن مزایایی از جمله شکلپذیری مناسب، سختی زیاد، میزان مقاومت برشی و جذب انرژی بالا همواره مورد توجه محققین بوده است. از سال 1980 میلادی که تحقیقات پایه برروی دیوار برشی فولادی بدون سخت‌کننده صورت پذیرفت، پیوسته پژوهشگران در صدد بهبود رفتار این سیستم، افزایش کارآیی و بهره‌وری آن بوده‌اند. از جمله اقداماتی که در جهت افزایش کارآیی و بهره‌وری دیوار برشی فولادی صورت پذیرفت، ایجاد بازشو بر روی ورق درونی بود. تحقیقات بر روی دیوار برشی فولادی دارای بازشو در اوایل دهه ی 90 میلادی با مطالعات صبوری قمی و رابرتز بر روی این سیستم آغاز گردید. در سال‌های اخیر یک نمونه دیوار برشی فولادی با بازشوهای منظم دایره ای شکل یا ماتریسی توسط محققان دانشگاه بوفالو آمریکا مطرح شده و مورد آزمایش قرار گرفت. از این نوع بازشو علاوه بر سیستمی جهت عبور تاسیسات در مواردی که ضخامت ورق مورد نیاز طراحی در دسترس نباشد میتوان استفاده نمود، به گونه‌ای که ورق ضخیم همراه با بازشوهای دایره ای شکل جایگزین ورق نازک بدون بازشو میگردد. در این مقاله نیز به جهت مطالعات بیشتر بر روی بازشوهای منظم دایره ای شکل، تاثیر اینگونه بازشو بر روی رفتار سیستم دیوار برشی فولادی مورد ارزیابی قرار می‌گیرد. بدین منظور یک نمونه دیوار برشی فولادی با بازشوهای دایره‌ای طراحی و ساخته شده سپس در مرکز تحقیقات سازه دانشگاه ارومیه تحت بارگذاری چرخه ای قرار گرفت. علاوه بر مطالعات آزمایشگاهی رفتار این نوع سیستم به صورت تحلیل عددی و با استفاده از نرم افزار المان محدود ABAQUS بررسی گردیده است. در نهایت نتیجه‌ی هر دو تحلیل آزمایشگاهی و عددی با روش تئوری آنالیز پلاستیک سازه مقایسه شده است. نتایج بدست آمده حاکی از تطابق مناسب پوش منحنی هیسترزیس در دو تحلیل عددی و آزمایشگاهی بوده همچنین نشان دهنده‌ی محافظه‌کارانه بودن روابط روش آنالیز پلاستیک و یا ضرایب کاهشی اعمال شده بر این روابط به سبب وجود بازشو و کاهش مقطع تیر میباشد. تفاصيل المقالة -
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219 - بررسی ظرفیت برشی و پیچشی و محصورشدگی تیرهای بتن آرمه مقطع مستطیلی با خاموت دورپیچ
حامد سفیدیان اشکان خدابنده لودر حالت کلی المان‌های بتن‌آرمه تمایل زیادی به تردشکنی دارند و این پدیده در هنگام لرزه به وضوح نمایان میگردد. یکی از مزایای محصور کردن بتن افزایش مقاومت بتن و شکلپذیری بتن است که اگر بتن به نحوی مناسب محصور شده باشد و اثر نیروهای لرزهای باعث کنده شدن بتن پوششی شود، بت أکثردر حالت کلی المان‌های بتن‌آرمه تمایل زیادی به تردشکنی دارند و این پدیده در هنگام لرزه به وضوح نمایان میگردد. یکی از مزایای محصور کردن بتن افزایش مقاومت بتن و شکلپذیری بتن است که اگر بتن به نحوی مناسب محصور شده باشد و اثر نیروهای لرزهای باعث کنده شدن بتن پوششی شود، بتن محصور شده به خوبی مقاومت می‌کند. بهترین شیوه برای این کار میتوان به خاموت گذاری به صورت مارپیچ اشاره کرد. در این پژوهش به بررسی تاثیر دورپیچ‌ها با توجه به متغییرهای گام دورپیچ‌ها و زاویه‌ی دورپیچ‌ها بر ظرفیت برشی و پیچشی تیرهای بتن مسلح مستطیلی پرداخته شده است. به منظور شبیه‌سازی نمونه‌ها از نرم‌افزار المان محدود ABAQUS استفاده شده است. نتایج نشان داد، زاویه‌ی ترکهای ایجاد شده در نمونه‌های دارای خاموت‌های بسته، بیشتر از نمونه‌ی متناظر(فاصله‌ی برابر گام‌ها در دورپیچ‌ها و خاموت‌های بسته) با دورپیچ‌هاست و استفاده از خاموت‌ها چه به صورت بسته و چه دورپیچ، ظرفیت برشی و پیچشی تیرهای بتن مسلح را به میزان قابل توجهی افزایش داده‌اند. مشخص گردید، تیرهای بتن مسلح دارای دورپیچ، ظرفیت برشی و پیچشی بیشتری نسبت به تیرهای بتن مسلح دارای خاموت بسته دارند.استفاده از خاموت‌های بسته و دورپیچ‌ها با فاصله‌ی گام‌های 80 میلیمتر به ترتیب ظرفیت برشی تیر بتن مسلح را 52% و 59% افزایش داده‌اند که اختلاف قابل توجهی است و با افزایش فاصله‌ی گام دورپیچ‌ها، از ظرفیت برشی و پیچشی تیرهای بتن مسلح کاسته می‌شود. با افزایش فاصله‌ی دورپیچ‌ها از 80 میلیمتر به 150 میلیمتر، ظرفیت برشی تیر بتن مسلح 30% کاهش یافته است که میزان قابل توجهی است. مطابق با نتایج، زاویه‌ی بهینه‌ی دورپیچ که عملکرد تیرهای بتن مسلح مستطیلی را در بهترین حالت قرار می‌دهد، 80 درجه میباشد. در این حالت زاویه‌ی ترکهای قطری کمتر از سایر حالات بوده و ظرفیت برشی و پیچشی آن به میزان قابل توجهی بیشتر از سایر نمونه‌ها با گام‌های برابر و زاویه‌های متفاوت دورپیچ است. تفاصيل المقالة -
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220 - ارائه یک رابطه محاسباتی جدید جهت ارزیابی ظرفیت باربری پی نواری واقع بر زمین دو لایه ی چسبنده ی- اصطکاکی
لقمان رحیمی نوید گنجیان مکائیل یوسف زاده فرد مهدی درخشندیدر این تحقیق به منظور ارائه ی یک رابطه تحلیلی جدید جهت ارزیابی ظرفیت باربری پی نواری واقع بر توده خاک دو لایه چسبنده ی اصطکاکی، 12 سری آزمون بار گذاری مدل فیزیکی برای سه تیپ لایه خاک فوقانی با تراکم و ضخامت های مختلف انجام شده است. در ادامه یک سری مطالعات پارامتریکی جهت أکثردر این تحقیق به منظور ارائه ی یک رابطه تحلیلی جدید جهت ارزیابی ظرفیت باربری پی نواری واقع بر توده خاک دو لایه چسبنده ی اصطکاکی، 12 سری آزمون بار گذاری مدل فیزیکی برای سه تیپ لایه خاک فوقانی با تراکم و ضخامت های مختلف انجام شده است. در ادامه یک سری مطالعات پارامتریکی جهت ارزیابی دقت رابطه پیشنهادی با استفاده از نرم افزار المان محدود PLAXIS 2D انجام گردید. جهت بررسی نتایج مدلسازی های عددی و کنترل صحت این مدلسازی ها، نتایج این تحلیل ها با نتایج آزمایش مدل های فیزیکی متناظر با در نظر گرفتن تاثیر پارامترهای مختلف(ضخامت نسبی، نسبت تراکم و پارامترهای مقاومت برشی لایه های خاک) بر مکانیسم خرابی و ظرفیت باربری خاک مقایسه شدند. با توجه به انطباق مناسب منحنی های بار-جابجایی، الگوی خرابی و متوسط اختلاف ظرفیت باربری در حدود 3/3 درصد بین مدل های فیزیکی و عددی، نشان می دهد مدل های اجزای محدود دارای دقت مناسبی در پیش بینی رفتار واقعی نمونه های آزمایشگاهی هستند و می توان به نتایج حاصل از شبیه سازی عددی اعتماد نمود. بعداز اطمینان ازصحت نتایج آنالیز عددی، مقادیر ظرفیت باربری بدست آمده از هر دو روش عددی و تحلیلی برای 88 حالت مختلف از پی نواری به ابعاد 1 و 2 متر و توده ی خاک با لایه بندی، عمق و پارامترهای مقاومت برشی متفاوت، با هم مقایسه گردید و اختلافی در حدود 7 و 5/12 درصد به ترتیب برای پی به ابعاد 1 و 2 متر مشاهده شد. این نتایج نشان دادند که توافق نسبتا خوبی بین هر سه روش تجربی، عددی و تحلیلی در ارزیابی ظرفیت باربری نهایی وجود دارد و رابطه تحلیلی می تواند با دقت نسبتا خوبی روند تغییرات فشار حدی برحسب ضخامت نسبی لایه ها و ارزیابی ظرفیت باربری نهایی برای حالات مختلفی از پی نواری واقع بر زمین دولایه را پیش بینی بکند. تفاصيل المقالة -
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221 - مطالعه عددی عملکرد قاب بتن مسلح دارای ورق پرکننده فولادی شکل‌پذیر با نقطه تسلیم پایین
امان اله حسن زاده رحیم آبادی یحیی نصیرا علی قمریدﻳﻮارﻫﺎی ﺑﺮﺷﻰ ﻓﻮﻻدی در ﻛﺎرﺑﺮدﻫﺎی اوﻟﻴﻪ ﺑﻴﺸﺘﺮ ﺑﺼﻮرت ﺗﻘﻮﻳﺖ ﺷـﺪه ﺑﻮدﻧـﺪ، اﻣـﺎ اﻣـﺮوزه ﺑﺮای ﭘﮋوﻫﺸﮕﺮان، ﻋﻤﻠﻜﺮد ﻣﻨﺎﺳﺐ دﻳﻮارﻫﺎی ﺑﺮﺷﻰ ﻓﻮﻻدی ﺑﺪون ﺳﺨﺖ ﻛﻨﻨـﺪه ﻣﺸـﺨﺺ ﺷـﺪه اﺳﺖ. زﻣﺎﻧﻰ ﻛﻪ ﺿﺨﺎﻣﺖ ورق ﻓﻮﻻدی و تنش تسلیم ﻛﻢ ﻣﻰﺑﺎﺷﺪ، ورق در ﺑﺎرﻫﺎی ﺑﺴﻴﺎر ﻛﻢ ﻛﻤـﺎﻧﺶ ﻧﻤـﻮده و ﻣﻜﺎﻧﻴﺰم ﺗﺤﻤﻞ ﺑﺎر أکثردﻳﻮارﻫﺎی ﺑﺮﺷﻰ ﻓﻮﻻدی در ﻛﺎرﺑﺮدﻫﺎی اوﻟﻴﻪ ﺑﻴﺸﺘﺮ ﺑﺼﻮرت ﺗﻘﻮﻳﺖ ﺷـﺪه ﺑﻮدﻧـﺪ، اﻣـﺎ اﻣـﺮوزه ﺑﺮای ﭘﮋوﻫﺸﮕﺮان، ﻋﻤﻠﻜﺮد ﻣﻨﺎﺳﺐ دﻳﻮارﻫﺎی ﺑﺮﺷﻰ ﻓﻮﻻدی ﺑﺪون ﺳﺨﺖ ﻛﻨﻨـﺪه ﻣﺸـﺨﺺ ﺷـﺪه اﺳﺖ. زﻣﺎﻧﻰ ﻛﻪ ﺿﺨﺎﻣﺖ ورق ﻓﻮﻻدی و تنش تسلیم ﻛﻢ ﻣﻰﺑﺎﺷﺪ، ورق در ﺑﺎرﻫﺎی ﺑﺴﻴﺎر ﻛﻢ ﻛﻤـﺎﻧﺶ ﻧﻤـﻮده و ﻣﻜﺎﻧﻴﺰم ﺗﺤﻤﻞ ﺑﺎر از ﺑﺮش درون ﺻﻔﺤﻪ ﺑﻪ ﻣﻴﺪان ﻛﺸﺸﻰ ﻗﻄﺮی ﺗﺒﺪﻳﻞ ﻣﻰ ﮔﺮدد. در این پژوهش عملکرد خمشی قاب بتن مسلح سه طبقه و یک دهانه که دارای ورق پرکننده فولادی شکل‌پذیر با نقطه تسلیم پایین می باشد، با استفاده از نرم‌افزار آباکوس مورد بررسی قرار گرفته است. تعداد نمونه های مورد بررسی در این پژوهش 45 مدل در نظر گرفته شد. پارامترهای مورد بررسی در این قاب بتن مسلح دارای دیوار برشی فولادی، تنش تسلیم دیوار برشی، ضخامت دیوار برشی و نسبت دهانه به ارتفاع میباشد و مولفه‌های سختی اولیه، نیروی تسلیم، نیروی ماکزیمم، جابجایی تسلیم و انرژی، مبنای مقایسه نمونه های عددی قرار گرفته است. نتایج این مطالعه عددی نشان داد، با تغییر پارامتر نسبت دهانه به ارتفاع، ضخامت و تنش تسلیم ورق فولادی با نقطه تسلیم پایین، بیشترین درصد افزایش مولفه سختی سکانتی 39/49، 59/45 و 67/59 درصد، بیشترین درصد افزایش مولفه مقاومت نهایی 64/27، 88/30 و 73/40 و بیشترین افزایش مولفه انرژی استهلاکی به ترتیب 35/32، 19/34 و 9/44 درصد حاصل شده است. در مدلهای عددی قاب‌های بتن مسلح دارای دیوار برشی فولادی از جنس ورق با نقطه تسلیم پایین، مود شکست ناشی از کمانش موضعی و چروک شدگی ورق پرکننده فولادی قاب و ترکهای موضعی در محل اتصال تیر به ستون در قاب بتن مسلح است. پارامتری که بیشترین تأثیر را بر مقدار تغییرات سختی، مقاومت خمشی و انرژی استهلاکی در قاب مورد مطالعه دارد، پارامتر تنش تسلیم ورق فولادی با نقطه تسلیم پایین میباشد. همچنین در ستونها و تیرها، ترکهای بتنی طولی به دلیل نیروی لنگر منتقل شده در اثر میدان کششی در صفحات پر کننده فولاد رخ داده است. تفاصيل المقالة -
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222 - اثر انفجارهای همزمان و چندمرحله‌ای بر پاسخ سازه‌های مدفون در خاک
سعید فیروزآبادی هادی دشتی علیرضا فیوضسازههای زیرزمینی بهترین گزینه برای احداث قرارگاه‌های فرماندهی و کنترل، پناهگاه‌ها، انبار سلاح‌ها و تجهیزات مهم و صنایع دفاعی می‌باشند. یکی از موضوعات مهمی که پیرامون آنها مطالعات نسبتاً محدودی انجام‌شده است و ممکن است در طراحی این نوع سازه‌ها لحاظ نشود، نحوه اعمال بار أکثرسازههای زیرزمینی بهترین گزینه برای احداث قرارگاه‌های فرماندهی و کنترل، پناهگاه‌ها، انبار سلاح‌ها و تجهیزات مهم و صنایع دفاعی می‌باشند. یکی از موضوعات مهمی که پیرامون آنها مطالعات نسبتاً محدودی انجام‌شده است و ممکن است در طراحی این نوع سازه‌ها لحاظ نشود، نحوه اعمال بارگذاری ناشی از پرتاب بمب‌های هواییِ هواپیماها بر روی سازه‌های مدفون زیرزمینی میباشد. وقوع بارهای انفجاری به‌صورت همزمان و چندمرحله‌ای ناشی از پرتاب موشک از هواپیما و پهبادها نیز پاسخ سازه‌ای مدفون را تحت تأثیر قرار می‌دهد. ازاین‌رو در مطالعه‌ی حاضر پس از صحت سنجی مدل عددی با یک مدل واقعی، به بررسی مقایسه‌ای اثر بمب‌های همزمان و چندمرحله‌ای بر پاسخ سازه‌های امن مدفون در خاک با استفاده از روش اجزاء محدود پرداخته‌شده است. بررسی این موضوع در چهار حالت با عمق دفن ثابت و موقعیت قرار گیری انفجار مختلف انجام گرفته است. نتایج حاصل از بیشینه تنش‌های ایجادشده نشان می‌دهد، که در حالت اعمال بارهای ناشی از بمب‌گذاری چندمرحله‌ای، سازه‌های زیرزمینی موردبررسی، در تمامی موقعیت‌های در نظر گرفته‌شده، متحمل تنش‌های بیشتری نسبت به حالت بارگذاری انفجاری هم‌زمان‌شده است. تفاوت این تغییرات در برخی نقاط تا حدود 15 درصد مشاهده گردیده است. تفاصيل المقالة -
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223 - مطالعه و بررسی رفتار ستون‌های کامپوزیتی فولادی پرشده با بتن کوتاه (غیر‌لاغر) با سطح مقطع هندسی (L) شکل تحت تحلیل حساسیت عددی (FEM) با بارگذاری فشاری محوری
سید علی موسوی داودی مرتضی نقی پوردر سالیان اخیر استفاده از مقاطع فولادی پر شده با بتن (CFST) به دلیل مزایای بسیار زیاد از جمله، عملکرد لرزهای عالی، استحکام بالا، انعطاف‌پذیری بالا و ظرفیت جذب انرژی نسبت به مقاطع بتنی (RC) و فولادی در صنعت ساختمان‌سازی گسترش زیادی پیدا کرده أکثردر سالیان اخیر استفاده از مقاطع فولادی پر شده با بتن (CFST) به دلیل مزایای بسیار زیاد از جمله، عملکرد لرزهای عالی، استحکام بالا، انعطاف‌پذیری بالا و ظرفیت جذب انرژی نسبت به مقاطع بتنی (RC) و فولادی در صنعت ساختمان‌سازی گسترش زیادی پیدا کرده است، این ستونها اغلب بیشتر در اشکال دایره‌ایی اجرا میگردد. دلیل اصلی این موضوع این نکته هست، که مقاطع دایره‌ای محصور شدگی بیشتری را نسبت به مقاطع دیگر در بتن هسته ایجاد می‌کند. این مهم سبب گردیده که مقاطع دایره‌ای نسبت به مقاطع دیگر در ستون‌های (CFST) بیشتر مورد استفاده قرار گیرد. اما در بعضی از مواقع استفاده از مقاطع دایره‌ایی غیر ممکن خواهد شد، از جمله این موارد میتوان رعایت ملاحظات معماری، اجرای اتصالات اقتصادی‌تر و آسان‌تر در مقاطع چهار‌گوش نسبت به مقاطع دایره‌ایی، را نام برد، این دلایل سبب میگردد، اشکال خاص از جمله مقاطع مربع و مسطیل و مقاطع با اشکال L و T شکل در بعضی از قسمتهای ساختمانی مورد استفاده قرار گیرد. با توجه به اهمیت این موضوع در این مقاله سعی گردید که به معرفی و بررسی رفتار مکانیکی ستون‌های کوتاه (CFST) با مقطع هندسی L شکل و بررسی اثر پارامتری ضخامت جدار فولاد، و تنش فشاری بتن، بر روی ظرفیت و رفتار مکانیکی این ستونها پرداخته شود، که در انتها و بعد از انجام تحلیل نمونه‌های مطالعاتی تحت روش اجزای محدود (FEM) مشخص گردید که در ستون‌های (CFST) اثر ضخامت جدار فولادی پارامتر تاثیرگذارتری بر روی ظرفیت و رفتار مکانیکی ستون‌های (CFST) با مقطع هندسی L شکل خواهد بود. تفاصيل المقالة -
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224 - بررسی تاثیر چرخش مثلثاتی ستون بر ظرفیت برش منگنه‌ای در دالهای مجوف دو طرفه با استفاده از روش المان محدود
هادی عزیزیان محمدعلی لطف الهی یقین علاءالدین بهروشبا توجه به اینکه اجرای ستون در دالهای مجوف دوطرفه با برخی محدودیت‌ها بخصوص معماری مواجه است، بنابراین در بعضی از اجراها، ستون، باید چرخش داده شود که این چرخش باعث تغییر فاصله گویهای کروی از لبه ستون و تغییر ظرفیت برش منگنه‌ای خواهد شد، که تاکنون در این زمینه تحقیقات آ أکثربا توجه به اینکه اجرای ستون در دالهای مجوف دوطرفه با برخی محدودیت‌ها بخصوص معماری مواجه است، بنابراین در بعضی از اجراها، ستون، باید چرخش داده شود که این چرخش باعث تغییر فاصله گویهای کروی از لبه ستون و تغییر ظرفیت برش منگنه‌ای خواهد شد، که تاکنون در این زمینه تحقیقات آزمایشگاهی و آنالیز عددی انجام نشده است. در این تحقیق بعد از کالیبراسیون نرم‌افزار المان محدود ABAQUS با نتایج آزمایشگاهی، تاثیر چرخش ستون مربعی با فواصل مختلف گویهای کروی از لبه ستون بر ظرفیت برش منگنه‌ای و مکانیسم شکست (ناحیه مستعد خرابی) در دال مجوف دو طرفه بررسی شده است. نتایج نشان می‌دهد با افزایش فاصله گویها از بر ستون تا ( ) با زاویه‌های مختلف، ظرفیت برش منگنه‌ای افزایش پیدا کرده سپس ثابت میگردد. در شرایطی که فاصله گوی‍ها از لبه ستون، کمتر از (d) باشد با افزایش زاویه چرخش ستون، ظرفیت برش منگنه‌ای کاسته می‌شود که علت این امر وجود ناحیه مستعد خرابی در فاصله کمتر از (d) میباشد. تفاصيل المقالة -
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225 - عملکرد منار تاریخی گسکر در برابر مخاطرات طبیعی باد و زلزله
مجید پورامینیان الهه دیده ورمنارهای آجری تاریخی از عناصر اصلی معماری ایران هستند و در سراسر کشور در ابعاد و ارتفاع های مختلف وجود دارند. در این مقاله منار آجری گسکر به ارتفاع متر به کمک مدلسازی اجزای محدود توسط برنامه نویسی APDL و گسسته سازی دقیق به منظور دستیابی به الگوی آسیب دقیق انجام گرفته اس أکثرمنارهای آجری تاریخی از عناصر اصلی معماری ایران هستند و در سراسر کشور در ابعاد و ارتفاع های مختلف وجود دارند. در این مقاله منار آجری گسکر به ارتفاع متر به کمک مدلسازی اجزای محدود توسط برنامه نویسی APDL و گسسته سازی دقیق به منظور دستیابی به الگوی آسیب دقیق انجام گرفته است. سپس تقاضای بار باد و بار زلزله مطابق مقررات ملی ساختمان تعیین و به سازه اعمال شده است. از ماکرومدل برای مدلسازی محیط مصالح بنایی استفاده شده است. خصوصیات غیرخطی نیز به مصالح اختصاص داده شده است. نتایج نشان داد که منار در برابر بارگذاری باد طرح و شدیدترین باد ثبت شده در دنیا ایمن است. در صورتی که تا 12 برابر فشار باد طرح به سطح بادگیر منار اعمال شود رفتار غیرخطی بنا آغاز میگردد. همچنین منار در برابر زلزله طرح آسیب پذیر بوده و آسیب های خفیف در پای منار ایجاد شده است و بیانگر این است که منار در معرض ریسک خرابی قرار دارد. تفاصيل المقالة -
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226 - بررسی رفتار ستون‌های بتن مسلح تحت اثر بارگذاری چرخه‌ای قبل و بعد از بهسازی با الیاف پلیمری
سینا خوارزمی علیرضا راسخی صحنهامروزه روند مقاوم سازی و بهسازی لرزه ای در کشورمان شتاب بیشتری به خود گرفته است و با توجه به این که اغلب ساختمان های موجود در کشورمان بافتی فرسوده و غیر استاندارد دارند، بررسی مقاوم سازی به ویژه در حیطه‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌ی ستون ها که از مهم ترین و حیاتی ترین اجزای سازه می أکثرامروزه روند مقاوم سازی و بهسازی لرزه ای در کشورمان شتاب بیشتری به خود گرفته است و با توجه به این که اغلب ساختمان های موجود در کشورمان بافتی فرسوده و غیر استاندارد دارند، بررسی مقاوم سازی به ویژه در حیطه‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌‌ی ستون ها که از مهم ترین و حیاتی ترین اجزای سازه می باشند، امری اجتناب ناپذیر است. لذا در این تحقیق به بررسی رفتار ستون های بتن مسلح تحت اثر بارگذاری چرخه ای قبل و بعد از بهسازی با الیاف پلیمری می پردازیم. در همین راستا جهت صحت سنجی مدل سازی از یک مطالعه آزمایشگاهی مناسب استفاده شده است. سپس در نرم افزار اجزای محدود آباکوس با شبیه سازی چندین مدل متنوع به بررسی نحوه مناسب آرایش مقاوم سازی الیاف پلیمری پرداخته شده است. پس از مطالعه نمودارهای هیسترزیس بار- جابجایی، نمودار پوش بار- جابجایی، بار نهایی و سهم الیاف پلیمری مدل‌ها، مشخص شد، نمونه هایی که الیاف پلیمری دارند دارای قابلیت تحمل بار بیشتر و همچنین جذب و استهلاک انرژی بیشتر نسبت به حالت بدون الیاف می باشند. تفاصيل المقالة -
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227 - مطالعه‌ی عددی رفتار اتصالات K شکل لوله فولادی پرشده با بتن
مصطفی عطارموسوی احمد ملکینقش اصلی اتصال، انتقال نیروها بین اعضاء سازه ای و حفظ یکپارچگی سازه تحت اثر بارهای وارده میباشد. بسیاری از خرابی های سازه ای صرفا بعلت نقص در طراحی و آنالیز اعضاء سازه ای اتفاق نمی افتد بلکه بیشتر بخاطر اهمیت ندادن به رفتار و طراحی اتصالات صورت می گیرد. حتی هنگامی که ن أکثرنقش اصلی اتصال، انتقال نیروها بین اعضاء سازه ای و حفظ یکپارچگی سازه تحت اثر بارهای وارده میباشد. بسیاری از خرابی های سازه ای صرفا بعلت نقص در طراحی و آنالیز اعضاء سازه ای اتفاق نمی افتد بلکه بیشتر بخاطر اهمیت ندادن به رفتار و طراحی اتصالات صورت می گیرد. حتی هنگامی که نیروهای اعضاء سازه‌ای بطور دقیق شناخته شده است، شناخت کاملی از رفتار اتصالات صورت نمی گیرد به همین دلیل در این تحقیق ابتدا یک اتصال K شکل تحت اثر بارگذاری یکنواخت توسط نرم‌افزار آباکوس مدلسازی شده و با نتایج آزمایشگاهی تحقیقات گذشته اعتبارسنجی گردیده است. سپس 8 مدل عددی تحلیلی با متغیرهای متفاوت شامل تنش تسلیم فولاد، مقاومت فشاری بتن، زاویه‌ی قرارگیری لولهی فولادی و وجود گل‌میخ توسعه یافته اند تا ویژگی های متفاوت پاسخ ها را پیش بینی کنند. نتایج کلی آنها نشان داد، استفاده از گل‌میخ در لولهی اصلی که با بتن پر شده بود، مقدار تنش فون‌میزس مصالح فولادی و تنش فشاری بتن پرکننده را افزایش داد. افزایش 25 و 50 درصدی تنش تسلیم لوله‌های فولادی فرعی، مقداربار نهایی اتصال را به ترتیب 9/22 درصد و 6/74 درصد و شکلپذیری آن را 9/24 درصد و 1/52 درصد افزایش داده است. کاهش زاویه‌ی مابین لوله‌های فرعی و لولهی اصلی دراتصال K شکل لوله فولادی نشان داد که با کاهش زاویه‌ی مابین لوله‌های فرعی و لولهی اصلی، مقداربار نهایی و سختی اولیه کاهش می‌یابد ولی شکلپذیری سازه افزایش می‌یابد. در کل میتوان نتیجه گرفت که افزایش تنش تسلیم لوله‌های فرعی بیشترین تاثیر را در بهبود رفتار اتصال K شکل داشت. تفاصيل المقالة -
حرية الوصول المقاله
228 - بررسی عددی اتصال پیشنهادی فلزی با استفاده از استاب ستون کوتاه
مهرداد طاهری پور فرزاد حاتمی برق رضا رؤفیدر سازه‌های آسیب دیده در زلزله‌های مختلف، تنها شواهد اندکی دال بر اینکه نواحی پلاستیک واقعاً تشکیل شده باشند وجود دارد. اکثر مطالعات انجام شده بر روی ایجاد مفصل پلاستیک در قسمتی از تیر تمرکز داشته، که این امر در صورت وقوع باعث آسیب غیر قابل جبران برای تیر می‌شود و أکثردر سازه‌های آسیب دیده در زلزله‌های مختلف، تنها شواهد اندکی دال بر اینکه نواحی پلاستیک واقعاً تشکیل شده باشند وجود دارد. اکثر مطالعات انجام شده بر روی ایجاد مفصل پلاستیک در قسمتی از تیر تمرکز داشته، که این امر در صورت وقوع باعث آسیب غیر قابل جبران برای تیر می‌شود و در صورت عدم وقوع مفصل پلاستیک در تیر سبب انتقال نیرویی بیش از لنگر پلاستیک تیر به اتصال و در نتیجه به ستون شده که این امر یا باعث شکست ترد اتصال می‌شود و یا منجر به آسیب دیدن ستون به ویژه چشمه اتصال خواهد شد. لذا در این تحقیق با هدف کاهش آسیب در تیر و ستون و امکان جایگزینی قطعات آسیب چهار اتصال با هندسه جدید ارائه شده است. در حالت کلی، اتصالات پیشنهادی با جایگزینی یک مقطع H یاI شکل همراه یا به جای ورق‌انتهایی به عنوان استاب ستون کوتاه پیشنهاد میگردد. در این مطالعه ابتدا یک نمونه مدل اجزاء محدودی از اتصال ورق انتهایی که ترکیب جوش و پیچ بوده و تحت بار گذاری متناوب قرار گرفته است، انتخاب و پس از صحت سنجی در نرم‌افزار آباکوس مطالعه برروی اتصالات پیشنهادی انجام پذیرفت. نتایج نشان می‌دهد ناحیه‌ی استاب، با رفتار غیرخطی، یک مفصل محدود کنترل شده، با شکل پذیری فوق العاده را بوجود می‌آورد. تسلیم به هنگام در استاب سبب رفتار فیوزی آن و عدم آسیب به تیر و ستون می‌شود و تنش و کرنش پلاستیک را به‌طور‌قابل ملاحظه ای در چشمه اتصال ستون کاهش می‌دهد. تفاصيل المقالة -
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229 - بررسی عددی اثر مانع دیواری شامل گویهایECO-LINE بر انحراف مسیرگسلش 45 درجه شیب لغز معکوس
نیما آجلی لاهیجی بهنام ادهمی غلامرضا قدرتی امیری الهام رجبیگسلش ناشی از زلزله به‌صورت گسیختگی از لایه‌های زمین و خاک عبور کرده و به سطح زمین می‌رسد و باعث آسیب به سازه‌های زیرساختی به‌ویژه پل‌ها میگردد، بدین منظور انحراف مسیر گسیختگی خاک در مجاورت سازه با روشهای نوین حائز اهمیت است. حفر مانع دیواری در مسیر انتشار گسیختگی و در أکثرگسلش ناشی از زلزله به‌صورت گسیختگی از لایه‌های زمین و خاک عبور کرده و به سطح زمین می‌رسد و باعث آسیب به سازه‌های زیرساختی به‌ویژه پل‌ها میگردد، بدین منظور انحراف مسیر گسیختگی خاک در مجاورت سازه با روشهای نوین حائز اهمیت است. حفر مانع دیواری در مسیر انتشار گسیختگی و در مجاورت سازه به‌عنوان یکی از راهکارهای مؤثر کاهش اثرات ثانویه (جابجایی سطح زمین، دوران فونداسیون و پایه‌های سازه) ناشی از این پدیده است. در این مقاله مطالعه و بررسی عددی یک مانع دیواری پرشده با گویهای Eco-Line در مجاورت فونداسیون یک پل بتنی به‌عنوان روشی جدید جهت انحراف مسیر گسلش ارائه گردید و تأثیر پارامترهای مختلف ازجمله تغییرات عرض، عمق و فاصله مانع دیواری از فونداسیون پل بر انحراف مسیر، گسل 45 درجه شیب‌لغز معکوس و تغییرات جابجایی قائم و دوران فونداسیون موردبررسی قرار گرفت. نتایج نشان داد، هنگامی‌که فاصله مانع دیواری تا پایه پل و همچنین عمق مانع به نحوی باشد که در مسیر انتشار امواج گسلش قرار گیرد به نحو مطلوبی امواج منحرف و کرنش پلاستیک، انرژی کرنش خاک و تغییر شکل سطح زمین تا 100 درصد و پاسخ سازه حداکثر تا 50 درصد کاهش می‌یابد و از آسیب به سطح زمین و سازه جلوگیری می‌کند. تفاصيل المقالة -
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230 - تحلیل بدنه سد دوقوسی بتنی بختیاری توسط کدنویسی المان محدود سه بعدی
امید بختیاری نژاد هوشنگ حسونی زاده احسان دریکوندتحلیل سدهای بتنی دوقوسی در شرایطی از دقت کافی برخوردارهستند که به درستی مدل شده و تحلیل المان محدود سه بعدی گردند.دراین مقاله با استفاده از روش المان محدود سه بعدی ، سد بتنی دوقوسی بختیاری تحلیل می شود. به این منظور، برنامه ADSHAPEکه قادر به مدلسازی بدنه انواع سد بتنی م أکثرتحلیل سدهای بتنی دوقوسی در شرایطی از دقت کافی برخوردارهستند که به درستی مدل شده و تحلیل المان محدود سه بعدی گردند.دراین مقاله با استفاده از روش المان محدود سه بعدی ، سد بتنی دوقوسی بختیاری تحلیل می شود. به این منظور، برنامه ADSHAPEکه قادر به مدلسازی بدنه انواع سد بتنی می باشد تحت محیط برنامهنویسیMATLAB کدنویسی می گردد. سپس ،اطلاعات خروجی آن به برنامه کدنویسی شده AD ANALYSIS داده می شود که قادر به تحلیل المان محدود سه بعدی بدنه سد می باشد.برای صحت سنجی وکالیبره کردن برنامه از مدل تیر طره با نتایج معلوم استفاده می شود.این روش تحت انواع حالت های المان بندی با نقاط گوسی متفاوت تحلیل و نتایج مقایسه می شود و اثر تغییر المان ها و نقاط گوسی در جوابها بررسی می گردد. سپس سد بختیاری با رعایت اصول صحیح مش بندی و مدلسازی دقیق، تحلیل شده و تنش ها و تغییرشکلهای بدنه بررسی می گردد.نتایج نشان دهنده دقت قابل قبول برنامه های کدنویسی شده در مدلسازی و تحلیل المان محدود سه بعدی سدبتنی بختیاری می‍باشد. تفاصيل المقالة -
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231 - Comparison of Conventional Salient-Pole Synchronous Generators and Permanent-Magnet-Assisted Salient-Pole Synchronous Generators based on Finite Element Analysis
Reza Ilka Yousef Alinejad-Beromi Hossein Asgharpour-AlamdariThis paper presents a novel salient pole synchronous generator i.e. permanentmagnet- assisted salient-pole synchronous generator (PMa-SGs). Due to saturation of conventional synchronous generators (SGs), permanent-magnet-assisted salientpole synchronous generators (PMa- أکثرThis paper presents a novel salient pole synchronous generator i.e. permanentmagnet- assisted salient-pole synchronous generator (PMa-SGs). Due to saturation of conventional synchronous generators (SGs), permanent-magnet-assisted salientpole synchronous generators (PMa-SGs) are presented. PMa-SGs are a new type of salient-pole synchronous machines with extra permanent magnets (PMs) between the adjacent pole shoes. Placing PMs between adjacent pole shoes leads to a reduction in flux saturation plus an increase in armature flux linkage. In other words, the generator can operate at higher capacity. In this paper, a comparative study is carried out between conventional SGs and PMa-SGs based on finite element analysis (FEA). This is done via simulation of a PMa-SG compared to a conventional SG. Simulation Results show superiority of PMa-SGs over SGs. In fact, in PMa-SG maximum flux density in stator core is increased and pole bodies are not saturated. Besides, PMa-SG has higher flux linkage compared to conventional SG. Therefore, higher voltage could be produced in the generator. In other words, the output performance of the PMa-SG is considerably better than that of a conventional SG. تفاصيل المقالة -
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232 - Finite element numerical modeling of geogrid-reinforced shallow foundation’s behavior on loose soils
Morteza AlemyparvinInvestigating of foundations actions on soil is one of the most important topics in geotechnical engineering. This behavior indicates the stability conditions of the foundation under structure loading on the foundation and soil responses. In this regard, the foundation& أکثرInvestigating of foundations actions on soil is one of the most important topics in geotechnical engineering. This behavior indicates the stability conditions of the foundation under structure loading on the foundation and soil responses. In this regard, the foundation’s behavior is affected by soil behavior and failure is likely. In recent years, the use of soil reinforced stabilization is considered as the most successful procedure to increase bearing capacity and reduce foundation’s settlements. In this paper by using finite element numerical modeling, attempted to evaluate the behavior of the geogrid-reinforced soil which conducted by Plaxis2D software. For this purpose, with the series of modeling, the soil- foundation behavior for both unarmed and reinforced conditions has been evaluated and the of geogrids performance was estimated. Based on the results of modeling, it has been determined that the geogrids has a good ability to improve and stabilize soil conditions. تفاصيل المقالة -
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233 - Numerical finite element modeling for earth-dam grouting and curtains wall design by Plaxis software
Reza Poursalim Alireza Alizade MajdiThe presented study provide the numerical view and finite element (FEM) based modeling for earth-dam sealing curtains wall in earth-dam by using grout injection procedure. In this regard the plaxis software was used to estimate the variations and provide the simulation أکثرThe presented study provide the numerical view and finite element (FEM) based modeling for earth-dam sealing curtains wall in earth-dam by using grout injection procedure. In this regard the plaxis software was used to estimate the variations and provide the simulation which is implemented in geometrical modeling, boundary conditions, assign materials properties, behavioral model, mechanical modeling and seepage analysis. Modeling conduced for two case groups related to before and after curtains wall design. According to the results of seepage analysis, it has been determined that when the sealing curtain is not applied, deformations due to stress, strain and pressure of the perforated water cause changes in the dam area and its expansion in sediments. On the other hand, the expansion of strain in the core range reflects the phenomenon of plastic behavior of the core and downstream, which is the result of in-situ stress and water pore-pressure in it. تفاصيل المقالة -
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234 - Deformations Analysis and Finite Element Numerical Modeling of Soil’s Excavations Improved by Soil Nailing
Morteza AlemyparvinApplication of soil nailing in stabilization of excavation operations in urban area’s constructions is most flexible and capable techniques for earth retention under soil mass instabilities. In general, the implementation of the soil nailing method is step-by-step أکثرApplication of soil nailing in stabilization of excavation operations in urban area’s constructions is most flexible and capable techniques for earth retention under soil mass instabilities. In general, the implementation of the soil nailing method is step-by-step, and this issue itself causes various and step-by-step changes in the excavation area. Therefore, by studying these stepwise deformations, it can be obtained the development of soil’s failure mass step-by-step. In this regard, presented article tried to investigate the stepwise deformations’ analysis in soil nailing operation in excavated soils using finite element numerical method and Plaxis2D software. The modeling was performed during four drilling stages and the changes in the slope stability as well as the deformations’ expansion in slope mass (sand and clay) were investigated. Based on the simulation results, it has been determined that with increasing depth, the degree of confidence in the slope (safety factor) for 2 different arrangements decreases step-by-step and the plastic area increases towards the bottom of the pit. But the nailing wall shows a good ability to curb instability. تفاصيل المقالة -
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235 - Application of micro-pile for excavated trench dynamic stabilization by using three-dimensional finite element numerical method
Leyla Hamedi Ali SanaeiradSoil improvement can be expressed as one of the most important applied achievements of geotechnical engineering to improve the resistance conditions and properties of soil mechanics in a wide range of soil materials. The purpose of the improvements is to achieve proper أکثرSoil improvement can be expressed as one of the most important applied achievements of geotechnical engineering to improve the resistance conditions and properties of soil mechanics in a wide range of soil materials. The purpose of the improvements is to achieve proper resistance of soils (especially loose soils) to failure, which can cause serious damage and costs to construction projects. The micro-pile is one of most effective stabilization methods, which is used in the materials’ limitations and it is more economical than other techniques. The present study is based on investigation on the micro-piles’ performance to the improvement of sandy soil’s slope under dynamic earthquake loading. Methodologically, the finite element numerical method and Plaxis3D software have been used to implement the loading conditions and evaluate the deformations that have occurred in loose body of slope. The modeling process can be divided into two modeling groups, including slope with and without reinforced by micro-piles which is indicate the improvement process based on deformation reduction by stabilization technique. According to the results of the numerical simulation, it has been found that the use of micro-piles can be very effective on slope stability of the excavated trench in loose soil. تفاصيل المقالة -
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236 - Three-dimensional Finite Elements Numerical Modeling for Strip Foundations on Granular Soils Reinforced with Micro-piles
Leyla Hamedi Ali SanaeiradIn the present study, the performance of micro-piles for the improvement of loose sandy soils under dynamic loading on strip foundations was investigated. For this purpose, finite element numerical method (FEM) by Plaxis3D software has been used to implement loading con أکثرIn the present study, the performance of micro-piles for the improvement of loose sandy soils under dynamic loading on strip foundations was investigated. For this purpose, finite element numerical method (FEM) by Plaxis3D software has been used to implement loading conditions and evaluate deformations in loose sandy soils below the strip. The modeling process includes geometrical, behavioral models, boundary condition, material properties and dynamic modeling which that implemented on both unreinforced and reinforced strip foundation by micro-pile. Based on the results of the study, it can be well stated that the implementation of micro-piles has been able to improve loose sandy soils in strip foundations under dynamic loading conditions. So, the use of micro-communities in improving soil conditions against similar soils can be suggested. تفاصيل المقالة -
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237 - Effect of Geogrid on Increasing the Bearing Capacity of Strip Foundations in Sandy Soils
Farhad Pirmohammadi Alishah Mehdi Kanani Mehdi Mohammadrezaei Sattar ShafieiOne of the geosynthetics that is used in different parts of the world under surface foundations is geotextile, and relatively valid texts are available on how to use it and increase its load. But other geosynthetics have been geogrids, which have increased the load-bear أکثرOne of the geosynthetics that is used in different parts of the world under surface foundations is geotextile, and relatively valid texts are available on how to use it and increase its load. But other geosynthetics have been geogrids, which have increased the load-bearing capacity of surface foundations in soft clay and silty loam soils. In this paper, our u/b variations are between 1 and 17.5 with step 205 and in three different b/B modes are 5, 10 and 15. Also, the b/B changes from 0.1 to 2 with a step of 0.25 and in three different u/B modes are equal to 0.25, 0.75 and 1. The purpose of this study is to compare the soil load in different cases of geogrid with non-geogrid. This comparison is also performed by the BCR dimensionless number, which is the result of dividing the armed soil load into the soil load without geogrid. The results of this paper showed that the presence of geogrid increases soil fertility, but from a certain extent onwards, this amount of fertility does not show much difference. In this ratio, the geogrid dimensions are equal to 17.5 times the dimensions of the foundation. The presence of geogrids increased the soil fertility, but from a distance onwards, this amount of fertility does not show much difference. This ratio is equal to 1.75 times the dimensions of the foundation. تفاصيل المقالة -
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238 - Numerical modeling and seismic behavior analysis of strip foundation on sandy soils
Morteza Alemyparvin Mehdi KouhdaraghThe present study studies and evaluates the interactions between the states of structure-soil interaction for strip foundations reinforced with pile pedestals under dynamic loads such as earthquakes. To do this, the first design of strip foundation on sandy soil attempt أکثرThe present study studies and evaluates the interactions between the states of structure-soil interaction for strip foundations reinforced with pile pedestals under dynamic loads such as earthquakes. To do this, the first design of strip foundation on sandy soil attempted to understand the geotechnical behavior of foundation under dynamic loading. The strip foundation is a regular procedure used to improve the dynamic response to earthquakes. As a methodology, the finite element method and Plaxis software were used to simulate the displacement and deformation condition of the soil-structure interaction. According to the results, the program was successfully implemented to model the strip reinforced foundations in saturated sandy soil under dynamic loading. تفاصيل المقالة -
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239 - The effect of different arrangements of longitudinal reinforcements on the capacity of wide concrete beams
Javad Mahdian pari alireza faroughiA beam that has a width greater than the width of the column connected to it is called a wide beam. Due to the reduction in the height of the beams in this type of system, many advantages are created, including reducing the costs of molding and construction, increasing أکثرA beam that has a width greater than the width of the column connected to it is called a wide beam. Due to the reduction in the height of the beams in this type of system, many advantages are created, including reducing the costs of molding and construction, increasing the execution speed, reducing the height of the floor and of course increasing the number of floors in high-rise buildings, as well as including Other advantages of these beams from the architectural point of view are the hiding of the beams in the roof of the structure. In concrete structure design, ductility is one of the important parameters. The ductile behavior of the structure has a significant effect in reducing the design forces caused by the earthquake due to its energy absorption and loss. The role of reinforcement in the ductility of concrete is very important. In this article, a concrete beam with six different types of longitudinal rebar arrangement has been selected for study and four-point loading has been applied to the models. All models have been analyzed in ABAQUS finite element software. The results indicate that; The pattern of placing the rebar crosswise and diagonally has less hardness, ductility and resistance than other models. The highest amount of energy absorption was related to the model with six bars in a trapezoidal arrangement. تفاصيل المقالة -
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240 - Nonlinear Analysis of Reinforced Concrete Columns with Fiber Reinforced Polymer Bars
Ehab M LotfyIn this paper, the results of an analytical investigation on the behavior of RC columns reinforced with fiber reinforced polymer bars FRP are presented and discussed. Nonlinear finite element analysis on 10-column specimens was achieved by using ANSYS software. The nonl أکثرIn this paper, the results of an analytical investigation on the behavior of RC columns reinforced with fiber reinforced polymer bars FRP are presented and discussed. Nonlinear finite element analysis on 10-column specimens was achieved by using ANSYS software. The nonlinear finite element analysis program ANSYS is utilised owing to its capabilities to predict either the response of reinforced concrete columns in the post-elastic range or the ultimate strength of a reinforced concrete columns reinforced by FRP bars. An extensive set of parameters is investigated including different main reinforcement ratios, main reinforcement types (GFRP, Steel), the transverse reinforcement ratios, and the characteristic compressive strength of concrete.A comparison between the experimental results and those predicted by the existing models are presented. Results and conclusions may be useful for designers, have been raised, and represented. تفاصيل المقالة -
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241 - Stability Analysis Of 3-d Conventional Pallet Rack Structures With Semi-rigid Connections
Kamal M. Bajoria Keshav K. Sangle Rajshekar S. TalicottiThis paper describe the three dimensional finite element modeling and buckling analysis ofconventional pallet racking system with semi rigid connection. In this study threedimensional models of conventional pallet racking system were prepared using the finiteelement pro أکثرThis paper describe the three dimensional finite element modeling and buckling analysis ofconventional pallet racking system with semi rigid connection. In this study threedimensional models of conventional pallet racking system were prepared using the finiteelement program ANSYS and finite element analysis carried out on conventional pallet rackswith the 18 types of column sections developed along with semi-rigid connections. Aparametric study was carried out to compare the effective length approach and the finiteelement method for accuracy and appropriateness for cold-formed steel frame design.Numerous frame elastic buckling analyses were carried out to evaluate the alignment chartand the AISI torsional-flexural buckling provisions. The parameters that influence the valueof Kx for column flexural buckling were examined in this study. The alignment chart and theAISI torsional-flexural buckling provisions, used to obtain the effective lengths and elasticbuckling load of members were also evaluated. Results showed that the elastic buckling loadobtained from the AISI torsional-flexural buckling provisions is generally conservativecompared to the results obtained from performing frame elastic buckling analysis. Resultsalso showed that, the effective length approach is more conservative than the finite elementapproach. تفاصيل المقالة -
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242 - Study of Dynamic Infinite Element Used for Soil Structure Interaction
Anand M. Gharad R. S. SonparoteStarting from two-dimensional (2D) equations of motion, discretized formulations for transient behavior of soil-structure interaction problems have been derived. Two different dynamic infinite elements taking into account single and two-wave types are presented in trans أکثرStarting from two-dimensional (2D) equations of motion, discretized formulations for transient behavior of soil-structure interaction problems have been derived. Two different dynamic infinite elements taking into account single and two-wave types are presented in transformed space. By coupling the infinite elements with standard finite elements, an ordinary finite element procedure is used for simulation of wave propagation in an unbounded foundation due to external forces. تفاصيل المقالة -
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243 - Finite Element Model Updating of a Frame with Direct and Sensitivity-Base Methods
مهدی تاجداری کاوه عباسیThis paper presents an overview of model updating and particularly its application for updating of frame model. In this article a mathematical model of the frame was produced with finite element method. The frame was subjected to hammer modal testing. Then the results o أکثرThis paper presents an overview of model updating and particularly its application for updating of frame model. In this article a mathematical model of the frame was produced with finite element method. The frame was subjected to hammer modal testing. Then the results of the modal testing were compared with those predicted with the model. This comparison revealed discrepancies between these two sets of results. It is a commonly known fact that incorrect values of parameters in a model, among other things, do cause these discrepancies. In order to improve the correlation between the measured and the predicted results and hence improve the reliability of the model, the model was subjected to finite element model updating. In this updating process, incorrect values of parameters in a model are adjusted. Also it is important in updating that the FE model be simple and in the same time can give good results.The objective of this article is to use direct and sensitivity-base methods for frame and also compare these methods. تفاصيل المقالة -
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244 - Propagation of Crack in Linear Elastic Materials Considering Crack Path Correction Factor
مهدی پورمحمودModelling of crack propagation by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture mechanics أکثرModelling of crack propagation by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture mechanics. Crack growth process is simulated by an incremental crack-extension analysis based on the maximum principal stress criterion, which is expressed in terms of the stress intensity factor. In this paper, a procedure to correct the direction of crack propagation in the analysis of finite element is peresented to ensure that a unique final crack path is achieved for different analysis of a problem by using different increments of crack. For each increment of crack extension, finite element method is applied to perform a single region stress analysis of the cracked structure. Results of this incremental crack extension analysis are presented for several geometries. تفاصيل المقالة -
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245 - Calculation of stress concentration around a hole in a hybrid composite lamina using finite element method
پژمان تقی پور پدرام لورزادهThe hybrid composites have exceptional properties such as strength to weight and hardness ratios. These characteristics make the application of these materials in the aerospace industry. In such industries, any defects in the form of holes or cracks will increase the te أکثرThe hybrid composites have exceptional properties such as strength to weight and hardness ratios. These characteristics make the application of these materials in the aerospace industry. In such industries, any defects in the form of holes or cracks will increase the tension in these materials and fail, which are very dangerous. In composite materials, there are various fittings, such as a bolt and a rivet, which is the focus of stress concentration in the joints because the fibers are damaged. In this research in hybrid composite materials, a high elastic modulus fiber (HM) and a low elastic modulus fiber (LM) are used. It is also assumed that the length of the sheet is infinite. The force on the lamina is tensile force which applies on matrix and fibers while the fibers in the layers are one directed. In this paper the effects of different parameters such as number of total fibers , number of broken fibers , the ratio of LM to HM fiber extensional stiffness , Hole dimension ratio are considered. By using finite element method (FEM) stress concentration around the hole in a hybrid composite lamina is calculated and compared by the results obtained by analytical method [1] via written codes for finite element method.In this research unlike reference the matrix can withstand tensile stress. The results of the validation showed that compared to the reference data are close to each other, indicating the correctness of the code written for the analysis. تفاصيل المقالة -
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246 - Modeling the human retina in patients with glaucoma
افسانه صافدل کامران حسنیGlaucoma is a major risk factor for blindness and causes loss of visual field due to retinal ganglion cell (RGC) destruction. Glaucoma is associated with high blood pressure, cardiovascular disease, and ocular blood flow. Vascular factors play an important role in the d أکثرGlaucoma is a major risk factor for blindness and causes loss of visual field due to retinal ganglion cell (RGC) destruction. Glaucoma is associated with high blood pressure, cardiovascular disease, and ocular blood flow. Vascular factors play an important role in the development of glaucoma. A number of retinal vascular parameters are measured for use in software from retinal imaging. The biomechanical model of the disease reveals that mechanical stress induced by IOP impairs the function of retinal ganglion cells. Due to the difficulty of direct retinal biomechanical measurement in determining ocular biomechanics, the current study uses modeling with significant limitations to make it easier to examine.The purpose of this article is to stimulate the human retina in patients with glaucoma. In this research, the applied stresses on the inner surfaces of the retina and its effects on the inner parts are studied. Intraocular pressure (IOP) is considered to be higher than 20 mm Hg. With this model, we can study stresses and strains in different and desired conditions. The way of applying load is compressive load on the retina تفاصيل المقالة -
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247 - Study of Effective Parameters on Stress and Displacement of Axisymmetric Corrugated Diaphragms
رضا سلامی ناصریان وحید کدخداییIn this paper, the axisymmetric corrugated diaphragm using finite element method will be discussed, so that half of these diaphragms’ cross sections and later the applied pressure will be considered. Following this, using the consequent equations and visual basic أکثرIn this paper, the axisymmetric corrugated diaphragm using finite element method will be discussed, so that half of these diaphragms’ cross sections and later the applied pressure will be considered. Following this, using the consequent equations and visual basic software, a computer program will be provided which receives the diaphragms’ particulars such as diameter, thickness, pressure and the form of object’s cross section as AutoCAD file and then it measures the maximal stress and displacement. Finally, the calculated values will be compared with the experimental values and Theoretical results using the above program and then it will become clear that the results of this research enjoy the acceptable precision. Then, the various parameters which have an influence on the displacement and stress are changed and the results of these changes will be investigated. تفاصيل المقالة -
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248 - Static, dynamic and free vibration analysis of functional graded porous plates based on first-order shear deformation theory
کامران عاصمی سعید خبری مسعود باباییin this study, static, dynamic and natural frequency responses of the functionally graded saturated porous plate have been investigated. Two types of distributions including symmetric nonlinear distribution of porosity and asymmetric nonlinear distribution of porosity i أکثرin this study, static, dynamic and natural frequency responses of the functionally graded saturated porous plate have been investigated. Two types of distributions including symmetric nonlinear distribution of porosity and asymmetric nonlinear distribution of porosity in the thickness direction of the plate have been considered. First-order shear deformation theory (FSDT) and Lagrange method are used to model the problem. Finite element and Newmark direct integration methods are used to solve the governing motion equations in time and space domains, and then the effect of different parameters such as porosity and Skempton coefficients, and two different types of porosity distribution, length to thickness ratio and boundary conditions on static and time responses, and natural frequencies of functionally graded saturated porous plate have been investigated. Results show that by increasing the Skempton coefficient will always reduce the displacement and amplitude of vibration . Also, increasing the porosity coefficient will increase the displacement تفاصيل المقالة -
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249 - Study of Reduce Harmonic and Increasing Positioning Determination in Variable Reluctance Resolver with Area Couplings
Roya Shmsali Hamid LesaniVariable reluctance (VR) resolvers are widely used in industrial applications such as aerospace, military, robotic, control of hybrid motors, and navigation for solar systems. Variable reluctance resolvers are preferred because of simplified structure and affordable pri أکثرVariable reluctance (VR) resolvers are widely used in industrial applications such as aerospace, military, robotic, control of hybrid motors, and navigation for solar systems. Variable reluctance resolvers are preferred because of simplified structure and affordable prices in many applications in comparison with to the coiled rotor resolvers. In this study, effect of variation of physical parameters including skewing and opening slots of stator is investigated. The performance of the proposed structure is simulated by using a 3-D time stepping finite element method. تفاصيل المقالة -
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250 - Characterization of Electromagnetic Force of the Transformer During the Occurrence of a Ferroresonance Phenomenon by FEM
Iman Rostami ahmad zare alireza shams saeid saberi firooziFerroresonance is a non-linear resonance which occurs between the capacitors of the cables, lines, and breakers and nonlinear inductance of the reactors and transformers when their core is saturated. Due to ferroresonance, it has been proved that large pulse currents pa أکثرFerroresonance is a non-linear resonance which occurs between the capacitors of the cables, lines, and breakers and nonlinear inductance of the reactors and transformers when their core is saturated. Due to ferroresonance, it has been proved that large pulse currents pass through the transformer winding which seems to cause severe electromagnetic forces on the transformer windings. This research work is aimed at characterizing the transformer behavior at ferroresonance mode and calculation of the electromagnetic forces applied on the windings. To this end, a 2D FEM model of a 25KVA distribution transformer is developed. The accuracy of the FEM model is validated by comparing the FEM results and those obtained from the analytical methods. The results of this study are of great importance in the electrical and mechanical design of transformers and their windings. . . . . . . . . . . . . . . . . . . . . . . . تفاصيل المقالة -
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251 - A New Restructured Shaded Pole Induction Motor- 3D Finite Element Analysis and Experimental Verification
Sadegh Shamlou Mojtaba MirsalimShaded pole induction motors, despite the simplicity and low cost, are difficult to analyze particularly in the equivalent circuit methods, due to the asymmetric structure, saturation, harmonics, inaccurate estimation of leakage inductances and skew. Hence, 3D numerical أکثرShaded pole induction motors, despite the simplicity and low cost, are difficult to analyze particularly in the equivalent circuit methods, due to the asymmetric structure, saturation, harmonics, inaccurate estimation of leakage inductances and skew. Hence, 3D numerical methods could be very useful in the design and optimization stage. This paper presents the 3D transient finite element analysis (3DTFEM) of a 1/60HP, 2-pole prototyped, restructured shaded pole induction motor that has been designed and optimized using genetic algorithm technique. Experimental test has been carried out by a hysteresis brake dynamometer to determine the motor performance. Detailed comparisons among 2D, and 3D finite-element analysis, and experimental results are presented, which confirm the potentials of the new restructured shaded pole motor to achieve lower cost and higher efficiency objectives than the previous designs. تفاصيل المقالة -
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252 - Prediction of Polymeric Insulator Leakage Current under Water Droplets Using Neural Network
Zahra Ghiasi Faramarz Faghihi A.A. Shayegani AkmalIn this paper, the parameters of electric field and leakage current (LC) amplitude in polymeric insulator are calculated using finite element method (FEM) and predicted in the neural network. The variable angle and electrical conductivity of water droplets are changed. أکثرIn this paper, the parameters of electric field and leakage current (LC) amplitude in polymeric insulator are calculated using finite element method (FEM) and predicted in the neural network. The variable angle and electrical conductivity of water droplets are changed. Increased electric field due to the presence of water droplets on the insulator surface causes the insulator breakdown probability. In this paper, for predicting the on the polymeric insulator leakage currents a neural network model was proposed, which could arrange for references to prevent contamination flashover. Through the study of a LC data obtained via the FEM simulation, the characteristics of the LC combined with BP neural network. Simulation results illustrate that enhancement in leakage current and electric field values are created when the values of the electrical conductivity and drop contact angle is increased. تفاصيل المقالة -
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253 - Design Optimization for Total Volume Reduction of Permanent Magnet Synchronous Generators
Reza Ilka Yousef Alinejad-Beromi Hossein Asgharpour-Alamdari Hamid YaghobiPermanent magnet synchronous generators (PMSGs) are novel generators which can be used in high-performance wind farms. High efficiency and flexibility in producing electricity from variable rotation make them good candidate for wind power applications. Furthermore, beca أکثرPermanent magnet synchronous generators (PMSGs) are novel generators which can be used in high-performance wind farms. High efficiency and flexibility in producing electricity from variable rotation make them good candidate for wind power applications. Furthermore, because these kinds of generators have no excitation winding, there is no copper loss on rotor; hence, they can operate at high power factor. Besides, performance characteristics of such generators could be further improved by design optimization. This paper presents design optimization of PMSGs used in small wind turbines using novel and efficient optimization algorithm i.e. Artificial Bee Colony (ABC) Algorithm. Then, a well-known optimization algorithm i.e. Genetic Algorithm (GA) is used to show the validity and efficiency of the before-mentioned algorithm. For this purpose, the necessary equations are provided. Objective function of this study is to reduce the total volume of motor. Case study of this study is a 5 kW, 220 V, 50 Hz, 100 rpm generator. Finally, results obtained by optimization are verified with Maxwell software which is based on finite element method (FEM). Comparison shows that the results of optimization approach are in good agreement with that of FEM ones. تفاصيل المقالة -
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254 - PENALTY METHOD FOR UNILATERAL CONTACT PROBLEM WITH COULOMB’S FRICTION FOR LOCKING MATERIAL
Salah Bourichi El EssoufiIn this work, we study a unilateral contact problem with non local friction of Coulombbetween a locking material and a rigid foundation. In the first step , we present the mathematicalmodel for a static process, we establish the variational formulation in the form of a أکثرIn this work, we study a unilateral contact problem with non local friction of Coulombbetween a locking material and a rigid foundation. In the first step , we present the mathematicalmodel for a static process, we establish the variational formulation in the form of a variationalinequality and we prove the existence and uniqueness of the solution. In the second step, usingthe penalty method we introduce the penalized problem numerical in the form of variationalequality where we replace the law behavior and the law contact of Sigorini . The we show theconvergence of the continuous penalty solution as the penalty parameter n tends towards infinity.Then, the analysis of the finite element discretized penalty method is carried out. تفاصيل المقالة -
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255 - اثرات تراکم بوته و مقادیر مختلف کود نیتروژن به صورت سرک بر عملکرد سیب زمینی در منطقه دماوند
آرش روزبهانی محمد مهدی میرزاییبه منظور بررسی اثرات توام تراکم بوته و مقادیر مختلف کود نیتروژن به صورت سرک بر عملکرد و اجزای عملکرد سیب زمینی، آزمایشی به صورت کرت های خرد شده در قالب طرح پایه بلوک های کامل تصادفی با چهار تکرار در سال 1383 در منطقه دماوند انجام شد. در این آزمایش سه تراکم 97/7، 29/5 و أکثربه منظور بررسی اثرات توام تراکم بوته و مقادیر مختلف کود نیتروژن به صورت سرک بر عملکرد و اجزای عملکرد سیب زمینی، آزمایشی به صورت کرت های خرد شده در قالب طرح پایه بلوک های کامل تصادفی با چهار تکرار در سال 1383 در منطقه دماوند انجام شد. در این آزمایش سه تراکم 97/7، 29/5 و 32/3 بوته در مترمربع و چهار سطح کود نیتروژنه صفر، 100، 200 و 300 کیلوگرم در هکتار به ترتیب به عنوان سطوح کرت های اصلی و فرعی انتخاب شدند. پس از برداشت محصول سیب زمینی صفاتی مانند تعداد غده در بوته، متوسط وزن غده، عملکرد غدهو درصد ماده خشک شده اندازه گیری و نتایج به دست آمده تجزیه واریانس گردید. نتایج نشان داد که اثر تراکم و کود نیتروژنه بر کلیه صفات از نظر آماری در سطح احتمال یک درصد معنی دار بود. در تراکم 29/5 بوته در مترمربع و کود نیتروژنه 200 و 300 کیلوگرم در هکتاردر اغلب صفات نسبت به سایر تیمارها برتر بودند همچنین بین تیمار کود نیتروژنه 200 و 300 کیلوگرم در هکتار برای اغلب صفات تفاوت معنی داری از نظر آماری مشاهده نشد. همچنین اثر متقابل تراکم بوته و کود نیتروژنه برای تمامی صفات از نظر آماری معنی دار بود. تفاصيل المقالة -
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256 - تاثیر قطع آبیاری در مرحله خورجین دهی و پر شدن دانه بر عملکرد و اجزای عملکرد ارقام کلزای پاییزه در شرایط آب و هوایی کرج
هومن نظامی رنجبر امیرحسین شیرانی راد حمید مدنی کیومرث کلارستاقیبه منظور ارزیابی اثرات قطع آبیاری در مراحل نهایی رسیدن ارقام جدید کلزا (Brassica napus L.)در سال زراعی 82-1383 در کرج آزمایشی به صورت فاکتوریل در قالب بلوکهای کامل تصادفی با چهار تکرار اجرا گردید. آبیاری در دو سطح شاملآبیاری مرسوم (آبیاری بر اساس 80 میلیمتر تبخیر از تشت أکثربه منظور ارزیابی اثرات قطع آبیاری در مراحل نهایی رسیدن ارقام جدید کلزا (Brassica napus L.)در سال زراعی 82-1383 در کرج آزمایشی به صورت فاکتوریل در قالب بلوکهای کامل تصادفی با چهار تکرار اجرا گردید. آبیاری در دو سطح شاملآبیاری مرسوم (آبیاری بر اساس 80 میلیمتر تبخیر از تشتک کلاس A) و شرایط قطع آبیاری از مرحله خورجین دهی به بعد و دوازده رقم کلزای پاییزه به نام های,BanjoOlpro,SLM046 ,,Hyola401 ,Ds29955 ,Okapi ,Celsius ,Elvis ,Sahara ,OperaHerkules و Sunday تیمارهای آزمایشی را تشکیل دادند. در این تحقیق غالب خصوصیات فنولوژیکی گیاه شامل ارتفاع بوته، تعداد خورجین در بوته، تعداد دانه در خورجین، وزن هزار دانه، عملکرد دانه، درصد روغن دانه، عملکرد روغن اندازه گیری شد. نتایج این بررسینشان داد که رقم Elvis با میانگین عملکرد 5212 کیلوگرم دانه و 2270 کیلوگرم روغن در هکتار بالاترین عملکرد دانه و روغن را در هر دو شرایط آبیاری به دست آورد. اختلاف عملکرد دانه در هر دو شرایط آبیاری 12% درصد بود و در مورد عملکرد روغن قطع آبیاری منجر به کاهش درصد روغن به میزان 6% درصد گردید. نتایج نشان داد که چهار رقم Sunday ,Sahara ,Olpro ,Elvis از نظر عملکرد دانه و روغن برتر در هر دو شرایط آبیاری بوده اند. تفاصيل المقالة -
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257 - اثرات شوری بر ویژگی‌های جوانه‌زنی سه گونه شبدر
نورالله عبدیبه منظور بررسی تاثیر غلظت‌های مختلف کلرور سدیم بر ویژگی‌های جوانه‌زنی گونه های مختلف شبدر، آزمایشی به‌صورت فاکتوریل و در قالب طرح کاملاً تصادفی در سه تکرار انجام گرفت. این آزمایش شامل سه گونه شبدر به نام‌هـای شبدر قـرمز(Trifolium pretense L.)، شبدر ایرانی(T. resupinat أکثربه منظور بررسی تاثیر غلظت‌های مختلف کلرور سدیم بر ویژگی‌های جوانه‌زنی گونه های مختلف شبدر، آزمایشی به‌صورت فاکتوریل و در قالب طرح کاملاً تصادفی در سه تکرار انجام گرفت. این آزمایش شامل سه گونه شبدر به نام‌هـای شبدر قـرمز(Trifolium pretense L.)، شبدر ایرانی(T. resupinatum L.) و شبدر سفید (T. repens L.) و غلظت های مختلف شوری شامل محلول های 0،100،150،200،250 و300 میلی‌مولار کلرور سدیم و آب مقطر به عنوان شاهد بود. نتایج حاصل نشان داد که با افزایش غلظت شوری، درصد جوانه‌زنی کاهش یافت، اثر غلظت های مختلف شوری بر گونه‎های مختلف معنی‌دار بود و همچنین اثر متقابل بین غلظت‌های مختلف شوری بر گونه‌ها نیز معنی‌دار بود. گونه‌ها از لحاظ تحمل به شوری به‌ترتیب عبارت بودند از شبدر ایرانی، شبدر قرمز و شبدر سفید. واکنش گونه‌های مختلف به سطوح مختلف شوری متفاوت بود، به طوری‌که با افزایش غلظت شوری، در شبدر ایرانی درصد جوانه‌های غیرعادی در شبدر قرمز درصد بذرهای جوانه نزده سخت و در شبدر سفید درصد بذرهای جوانه نزده نرم، افزایش نشان داد. تفاصيل المقالة -
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258 - پارامترهای جدول زندگی و تولید مثل سن شکارگر Reuter Orius albidipennis روی مراحل مختلف سنی کنه دولکه‌ای Tetranychus urticae Koch
کریم اسکندرلی علی‌اصغر طالبی رضا وفایی‌شوشتری حسینی نیا حسینی نیاسن شکارگرOrius albidipennis یکی از عوامل کنترل بیولوژیک برخی از آفات گیاهی در ایران میباشد. در این تحقیق پارامترهای جدول زندگی و تولید مثل این سن در اتاقک رشد تحت شرایط دمایی 1±25 درجه سانتی گراد ، رطوبت نسبی 10±65 درصد و دوره نوری 14 ساعت روشنایی و10 ساع أکثرسن شکارگرOrius albidipennis یکی از عوامل کنترل بیولوژیک برخی از آفات گیاهی در ایران میباشد. در این تحقیق پارامترهای جدول زندگی و تولید مثل این سن در اتاقک رشد تحت شرایط دمایی 1±25 درجه سانتی گراد ، رطوبت نسبی 10±65 درصد و دوره نوری 14 ساعت روشنایی و10 ساعت تاریکی با تغذیه از مراحل مختلف سنی کنه دولکه‌ای، Tetranychus urticae مورد ارزیابی قرار گرفت. آزمایش با استفاده از 100 تخم یک روزه سن شروع و میزان مرگ و میر مراحل مختلف سنی به صورت روزانه تعیین گردید. نتایج نشان داد مرگ و میر ویژه سنی(qx) پوره‌های O. albidipennisدر 4 روزگی شروع و با نوسانات جزیی به تدریج افزایش یافت. امید به زندگی بعد از خروج پوره‌ها از تخم اندکی افزایش یافت ولی پس از آن روند کاهشی نشان داد. امید به زندگی در زمان خروج پوره ها از تخم 86/18 روز و در زمان ظهور حشرات کامل 97/12روز برآورد گردید. نرخ ناخالص باروری، بارآوری و تفریخ به ترتیب 42/0±45/76، 39/2±12/60 و 79/0 محاسبه گردید. همچنین میانگین تعداد تخم تولید شده توسط هر فرد ماده در هر روز 25/4 تخم به دست آمد تفاصيل المقالة -
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259 - کارایی دو روش رهاسازی تخم بالتوری سبز با نسبت 1:5(شکار: شکارگر) در شرایط گلخانه
زهرا رفیعی کرهرودی بیژن حاتمیبالتوریها از حشرات شکارگری هستند که در برنامه‌های مبارزة بیولوژیک به میزان زیادی مورد استفاده قرار گرفته‌اند. در این میان بالتوری سبزChrysoperla carnea (Steph.) (Neuroptera: Chrysopidae) بیشترین توجه را به عنوان یک عامل مبارزة بیولوژیک امیدبخش برای آفات گلخانه ای و مزر أکثربالتوریها از حشرات شکارگری هستند که در برنامه‌های مبارزة بیولوژیک به میزان زیادی مورد استفاده قرار گرفته‌اند. در این میان بالتوری سبزChrysoperla carnea (Steph.) (Neuroptera: Chrysopidae) بیشترین توجه را به عنوان یک عامل مبارزة بیولوژیک امیدبخش برای آفات گلخانه ای و مزرعه ای به خود جلب نموده است. در تحقیق حاضر دو روش رهاسازی تخم بالتوری، به صورت پاشیدن تخم به صورت مخلوط با خاک‌ارة نرم به عنوان مادة حامل تخم و استفاده از کرایزوبگ(کیسه‌های توری مخصوص) در گلخانه روی گیاه خیارCucumis sativum L. و شتة سبز جالیزAphis gossypii Glover مقایسه شدند. مقایسة نسبت رهاسازی 1:5 با دو روش رهاسازی در شرایطی که در هر قفس 4 گیاه بود، در قالب طرح بلوک کامل تصادفی انجام شد. اولین رهاسازی تخم بالتوری نشان داد که بین دو روش اختلاف معنی‌دار نبود و 80-84 درصد نسبت به شاهد کاهش رشد جمعیت شته مشاهده شد. اما تکرار رهاسازی یک هفته بعد از اولین رهاسازی، 94-95 درصدکاهش رشد جمعیت شته را نشان داد. چنانچه آزمایش‌ها در قفس و بدون حضور شکارگرهای عمومی تخم ولارو بالتوری مانند مورچه انجام شود هر دو روش در کنترل شته دارای اثر یکسان هستند. در روش رهاسازی تخم با خاک اره نکروزه شدن برگ ها مشاهده شد که در روش کرایزوبگ روی گیاه میزبان دارای اثر سوء نبود. گرچه کارایی هر دو روش در رهاسازی تخم بدون حضور شکارگرهای عمومی یکسان بود ولی از آنجایی که روش کرایزوبگ تخم‌ها را از حملة شکارگرهای تخم حفظ می‌کند بنابراین جهت استفاده در شرایط گلخانه‌های تجاری که مورچه‌ها و دیگر شکارگرهای عمومی حضور دارند مناسب‌تر میباشد. تفاصيل المقالة -
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260 - تحلیل خستگی در شاتون تراکتور یونیورسال مدل U650 به روش المان محدود با استفاده از نرم افزارANSYS
سید‌احمد میره‌ای محمود امید علی جعفریدر این تحقیق میزان خستگی شاتون تراکتور رومانی مدل U650 با روش المان محدود و استفاده از نرم افزار ANSYS محاسبه و طول عمر مفید آن بعد از106 بارگذاری به دست آمده است. هدف از انجام این تحقیق بررسی رفتار شاتون در برابر پدیده خستگی ناشی از بارهای تکراری وارده به آن بوده است. أکثردر این تحقیق میزان خستگی شاتون تراکتور رومانی مدل U650 با روش المان محدود و استفاده از نرم افزار ANSYS محاسبه و طول عمر مفید آن بعد از106 بارگذاری به دست آمده است. هدف از انجام این تحقیق بررسی رفتار شاتون در برابر پدیده خستگی ناشی از بارهای تکراری وارده به آن بوده است. نتایج این بررسی می تواند ضمن صرفه جویی در وقت و هزینه به بهینه سازی در طراحی قطعه کمک نماید. با انجام تحلیل های گسترده، محل یا گره های بحرانی که احتمال رشد ترک در آنها بیشتر از دیگر نواحی میباشد مشخص گردند. نتایج بررسی ها بحرانی‌ترین محل را در نزدیکی گژن پین با حداکثر تنش 793/26 مگاپاسکال نشان می دهد. این گره هم در بارگذاری کششی و هم در بارگذاری فشاری جزء گره های بحرانی مدل بوده است. با بارگذاری کاملا معکوس تعداد سیکل های مجاز اعمال نیرو برابر با 108 سیکل به دست آمد که این مقدار با کاهش ضرایب تمرکز تنش افزایش می‌یابد. نتایج فوق و همچنین سایر نتایج حاصله از تحقیق حاضر در فرایند بهینه سازی طراحی شاتون مفید می باشد. تفاصيل المقالة -
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261 - Numerical study on the effect of input variations on bulge height in hot tube metal gas forming process
مهدی چوگان محسن لوح موسوی.Hot metal gas forming of tubes can be used in various industries such as automotive and aerospace industries. In this process tube is formed at elevated temperatures, by using gas instead of fluid pressure. Lower required pressure and low power are its advantages in co أکثر.Hot metal gas forming of tubes can be used in various industries such as automotive and aerospace industries. In this process tube is formed at elevated temperatures, by using gas instead of fluid pressure. Lower required pressure and low power are its advantages in comparison to hydroforming process. In this paper, a hot metal gas bulging process of an aluminum alloy tube has been investigated by finite element method. In addition, The HMGF process was simulated by ) Dynamic, Temp-Disp, Explicit( because of the temperature distribution along the tube length, whereas temperature was simplified and assumed to be uniform in analytical method. The bulge height parameter was investigated by changing the input variations such as internal pressure, outer diameter, die entry radius, initial tube length and initial tube wall thickness in numerical method. The numerical result shows that the input variations have significant effects on tube bulge height in this process. تفاصيل المقالة -
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262 - Evaluating the impact of length and thread pitch on the stress distribution in dental implants and surrounding bone using finite element method
مسیح فیروزبخت حامد عجبی نائینی مصطفی پیرمرادیانlongevity of osseointegrated implants are intensely influenced by biomechanical factors. Control of these factors prevents mechanical complications, which include fracture of screws, components, or materials veneering the framework. In this study, the impact of length a أکثرlongevity of osseointegrated implants are intensely influenced by biomechanical factors. Control of these factors prevents mechanical complications, which include fracture of screws, components, or materials veneering the framework. In this study, the impact of length and threads pitch of dental implants on the stress distribution and maximum Von Mises stress in implant-abutment complex and jaw bone are studied using finite element method. The implant length changes from 8.5 mm to 13 mm and a range of 0.6 mm to 1 mm is considered for the threads pitch of implants. The maximum stresses are observed in implant-abutment complex, cortical bone and cancellous bone, respectively. Results suggest a length of 13 mm in a pitch of 0.7 mm for implants. Also, an optimal ratio for the pitch and length of an implant is proposed. تفاصيل المقالة -
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263 - A new plan to connect aluminum tubes of subsurface structures
غلامرضا مزروعی علی حیدریIn this study, a new method for joining aluminum tubes in subsurface structures using steel converting and aluminum welding are presented and reviewed. But near the weld area is under high thermal cycle and will cause residual stresses in heat affected zone. Therefore f أکثرIn this study, a new method for joining aluminum tubes in subsurface structures using steel converting and aluminum welding are presented and reviewed. But near the weld area is under high thermal cycle and will cause residual stresses in heat affected zone. Therefore for assessment of proposed connection from the perspective of residual stress by using the finite element method welding of tubes has been modeled in three dimensions. Thermal history is determined from thermal analysis and then the residual stresses due to welding are calculated. Because of the sensitivity of subject, the simulation process and properties are validated. The mechanical and thermal properties have been considered as a function of temperature. According to current, voltage and speed electrode, heat flux is applied by Goldak's heat source model. The modeling results were good agreement with experimental results and show that the initiative plan can be used to connect aluminum tubes of subsurface structures. تفاصيل المقالة -
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264 - Numerical study on the effect of hammering pressure on thickness reduction in hot tube metal gas forming process
علی طالبی انارکی محسن لوح موسویNowadays, light weight and high strength metals are being used in various industries such as automotive and aerospace. Using aluminum-magnesium alloys is an efficient way to reduce the weight of a specific part. These alloys have poor formability in room temperature thu أکثرNowadays, light weight and high strength metals are being used in various industries such as automotive and aerospace. Using aluminum-magnesium alloys is an efficient way to reduce the weight of a specific part. These alloys have poor formability in room temperature thus they should be formed at elevated temperature. Warm hydroforming and hot metal gas forming are conventional methods to form aforementioned alloys. It is proven that using hammering pressure is an efficient way in order to optimize hydroforming process that it improves formability and thickness distribution. In this paper, the effect of hammering pressure on hot free bulging of an Al6063 tube is investigated numerically and the results are compared with the results of constant pressure path. Results show that reduction of thickness is greater for peak constant pressure while using hammering pressure, due to gradual thickness reduction, could improve formability and thickness distribution. Results also show that axial feeding, increase the effect of formability caused by hammering pressure. تفاصيل المقالة -
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265 - Stress intensity factor at the hole-edge cracks tips in a finite plate
Mohammad Rahim TorshizianIn the current research work, the problem of fracture mechanics in a plate with a central hole under tensile loading is studied. The stress intensity factors are calculated for a finite plate containing two symmetrical hole-edge cracks. The problem is solved by two diff أکثرIn the current research work, the problem of fracture mechanics in a plate with a central hole under tensile loading is studied. The stress intensity factors are calculated for a finite plate containing two symmetrical hole-edge cracks. The problem is solved by two different methods, namely the finite element method and the FRANC software analysis. At first the finite element method is used and by writing a program in MATLAB software the stress intensity factors at the crack tips are calculated. The same problem is then reanalyzed with the Franc software and the results are compared. The effects of various factors such as the hole diameter, crack length and crack angle have been investigated on stress intensity factors. The results show that for small crack lengths, the effect of cracks length is more than that of the hole diameter on variation of normalized stress intensity factors, while it is the opposite for large crack lengths, the effect of hole diameter is more than that of the cracks length on variation of normalized stress intensity factors. تفاصيل المقالة -
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266 - Thermo-mechanical analysis of a coated cylinder head
Hojjat AshouriThis paper presents finite element analysis (FEA) of a coated and uncoated cylinder heads of a diesel engine to examine the distribution of temperature and stress. A thermal barrier coating system was applied on the combustion chamber of the cylinder heads, consists of أکثرThis paper presents finite element analysis (FEA) of a coated and uncoated cylinder heads of a diesel engine to examine the distribution of temperature and stress. A thermal barrier coating system was applied on the combustion chamber of the cylinder heads, consists of two-layer systems: a ceramic top coat (TC), made of yttria stabilized zirconia (YSZ), ZrO2-8%Y2O3 and also a metallic bond coat (BC), made of Ni-Cr-Al-Y. The coating system in this research comprises 300 μm zirconium oxide TC and 150 μm BC. The three-dimensional model of the cylinder heads was simulated in abaqus software and a two-layer viscoplasticity model was utilized to investigate the elastic, plastic and viscous behavior of the cylinder heads. The elastic and plastic properties of BC and TC layers were considered and the effect of thermal barrier coatings on distribution of temperature and stress was investigated. The aim of this study is to compare the distribution of temperature and stress in the coated and uncoated cylinder heads under thermo-mechanical loads. The results of FEA showed that the thermal barrier coating system reduces the temperature about 53°C because of its lower thermal conductivity. As a result, the cylinder heads tolerates lower temperature and fatigue life will increase. The results of thermo-mechanical analysis indicated that the stress in the coated cylinder heads decreased approximately 24 MPa for the sake of depletion of temperature gradient which can lead to higher fatigue lifetime. تفاصيل المقالة -
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267 - Experimental Investigation and Numerical Prediction of Fatigue Life in Force Fitted Fastener Holes
Hadi Taghizadeh Tagbakhsh ChakherlouIn this paper, the effect of interference fit on fatigue life of holed plate of mechanical joints was investigated experimentally. Fatigue tests were carried out on the holed specimens of Al-alloy 7075-T6 alloy. The interference fit process consists of force fitting a f أکثرIn this paper, the effect of interference fit on fatigue life of holed plate of mechanical joints was investigated experimentally. Fatigue tests were carried out on the holed specimens of Al-alloy 7075-T6 alloy. The interference fit process consists of force fitting a fastener into the hole with a negative clearance (diameter of the fastener is larger than of the hole) that produces beneficial tangential pre-stress at the edge of the hole. Stress and strain analysis was implemented in order to estimate the fatigue life due to interference fit process. 3D finite element simulations have been performed to obtain stress and strain histories and distributions around the hole due to interference fit and subsequent cyclic longitudinal loading using ANSYS package. The results obtained from the finite element analysis of the interference fit were employed to predict the fatigue life. The fatigue life was divided into two phases of crack initiation life and fatigue crack growth life. Fatigue initiation life was estimated using Fatemi–Socie multiaxial fatigue criterion, and the fatigue crack growth life was predicted using AFGROW computer code. The results show that there is a good agreement between the numerically predicted total fatigue life and experimental fatigue test results تفاصيل المقالة -
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268 - Experimental Study of the Effect of Laser-Cutting Process Parameters on Heat Distribution and Cutting Edge Quality of Steel Sheets
Mahsa Mokhtarian Azam GasemiThis study aimed to evaluate Laser-cutting process of Mild Steel St37 sheets with two different thicknesses. In order to evaluate the quality of cutting edge and the depth of the area affected by the heat, several tests were conducted to determine the effect of paramete أکثرThis study aimed to evaluate Laser-cutting process of Mild Steel St37 sheets with two different thicknesses. In order to evaluate the quality of cutting edge and the depth of the area affected by the heat, several tests were conducted to determine the effect of parameters such as Laser power, Laser beam movement speed and pressure of axillary gas on the quality of cutting edge and the depth of the area affected by the heat. The results showed that three main parameters of Laser beam movement speed, the pressure of axillary gas and Laser power can affect surface roughness and depth of the area affected by the heat. The value for each of these main parameters should be optimized based on other parameters and in a predetermined range in order to reach optimal conditions and edge quality and to use the interaction of these parameters to determine the final optimal conditions. تفاصيل المقالة -
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269 - Thermo-mechanical fatigue simulation of exhaust manifolds
Hojat AshoriLoading conditions and complex geometry have led the exhaust manifolds heads to become the most challenging parts of diesel engines. Thermal fatigue failure of the engine components easily happens due to excessive temperature gradient and thermal stress. Modern exhaust أکثرLoading conditions and complex geometry have led the exhaust manifolds heads to become the most challenging parts of diesel engines. Thermal fatigue failure of the engine components easily happens due to excessive temperature gradient and thermal stress. Modern exhaust systems must withstand severe cyclic mechanical and thermal loads throughout the whole life cycle. This study focuses on the Thermo-mechanical Fatigue (TMF) analysis for exhaust manifolds. The three-dimensional model of the exhaust manifolds was simulated in abaqus software and a chaboche model was utilized to investigate the elastic and plastic behavior of the exhaust manifolds. The numerical results showed that the temperature and thermal stresses have the most critical values at the confluence region of the exhaust manifolds. This area was under the cyclic tensile and compressive stress and then is under low cycle fatigue. After several cycles the fatigue cracks will appear in this region.The lifetime of this part can be determined through finite element analysis instead of experimental tests. تفاصيل المقالة -
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270 - Using finite element model in calculation of stress concentration factor around an elliptical hole in composite hybrid lamina
Pedram LorzadehThe hybrid composites have exceptional properties such as strength to weight and hardness ratios. These characteristics make the application of these materials in the aerospace industry. In composite materials, there are various fittings, such as a bolt and a rivet, whi أکثرThe hybrid composites have exceptional properties such as strength to weight and hardness ratios. These characteristics make the application of these materials in the aerospace industry. In composite materials, there are various fittings, such as a bolt and a rivet, which is the focus of stress concentration in the joints because the fibers are damaged. In this research in hybrid composite materials, a high elastic modulus fiber (HM) and a low elastic modulus fiber (LM) are used. It is also assumed that the length of the sheet is infinite. The force on the lamina is tensile force which applies on matrix and fibers while the fibers in the layers are one directed. In this paper the effects of different parameters such as ,number of broken fibers and the ratio of (LM) to (HM) fiber extensional stiffness.By using finite element method (FEM) modeling and investigation geometrical and crack modeling, stress concentration factor (SCF) around a elliptical hole is calculated and compared with the results obtained from reference.The results of the validation showed that compared to the reference data are close to each other, indicating the correctness of the code written for the analysis. تفاصيل المقالة -
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271 - Effect of residual stress in low cycle fatigue for coated exhaust manifold
Hojjat ashouriThe exhaust manifolds are subjected to higher loads than before, due to the increasing power output, fuel consumption and exhaust gas emission. Thus, simulation and analysis of fatigue cracks is essential. The effect of residual stress on the thermal stress and low cycl أکثرThe exhaust manifolds are subjected to higher loads than before, due to the increasing power output, fuel consumption and exhaust gas emission. Thus, simulation and analysis of fatigue cracks is essential. The effect of residual stress on the thermal stress and low cycle fatigue (LCF) life of exhaust manifolds using strain life methods was investigated. For this purpose, Solidworks software was used to model the exhaust manifolds. Then the thermo-mechanical analysis was carried out to determine the temperature and stress distribution in ANSYS software. Finally, the fatigue life prediction that considers residual stress effect was done. The simulated results proved that the thermal stresses and number of cycles to failure have the most critical values at the confluence region of the exhaust manifolds. The LCF results showed that the number of failure cycles for coated exhaust manifold is about 89% higher than the results obtained from the uncoated exhaust manifolds. Evaluating the residual stress, the TBC improves the number of failure cycles approximately 52% in comparison the uncoated exhaust manifold. The results of FEA proved a very good agreement between numerical simulation results and LCF analysis results, performed in references. تفاصيل المقالة -
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272 - Stabilized crack-opening stresses as a function of R-ratios and stress levels
Rahi Chermahini Majid JabbariAn elastic-perfectly plastic middle crack tension aluminum 2024-T3 alloy was used under plane stress, plane strain and 3D analysis to determine stabilized crack-opening stresses for different R-ratios and stress levels. The stabilized crack-opening stresses of a 3D anal أکثرAn elastic-perfectly plastic middle crack tension aluminum 2024-T3 alloy was used under plane stress, plane strain and 3D analysis to determine stabilized crack-opening stresses for different R-ratios and stress levels. The stabilized crack-opening stresses of a 3D analysis locate between those values of plane stress and plane strain conditions. Using the above strategy, one can determine crack-opening stresses for any desired thickness value using interpolating scheme. Two and three dimensional programs were developed based on small strain elasticity theory incorporating linear strain isoparametric elements. The plasticity part of the analysis uses initial stress approach. The crack was extended one element size as the applied load reached the maximum value of each load cycle. Crack opening and closure stresses of nodes on the crack surface plane after some cyclic crack extensions are demonstrated. Based on the obtained results, for the three-dimensional finite-element analysis, the calculated stabilized crack opening stresses always locate between those of plane stress and plane strain conditions. تفاصيل المقالة -
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273 - Modified Fixed Grid Finite Element Method to Solve 3D Elasticity Problems of Functionally Graded Materials
محمد جواد کاظم زاده پارسی فرهنگ دانشمندIn the present paper, applicability of the modified fixed grid finite element method in solution of three dimensional elasticity problems of functionally graded materials is investigated. In the non-boundary-fitted meshes, the elements are not conforming to the domain b أکثرIn the present paper, applicability of the modified fixed grid finite element method in solution of three dimensional elasticity problems of functionally graded materials is investigated. In the non-boundary-fitted meshes, the elements are not conforming to the domain boundaries and the boundary nodes which are used in the traditional finite element method for the application of boundary conditions no longer exist. Therefore, special techniques are needed for computation of the stiffness matrix of boundary intersecting elements and application of boundary conditions.The stiffness matrix of boundary intersecting elements are calculated via integration of strain energy over the internal parts of these elements. Essential boundary conditions are applied using penalty function method. To examine the effectiveness of the proposed method, some numerical examples are solved and results are compared with those obtained using the standard finite element method. تفاصيل المقالة -
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274 - The Effect of Inclined U-Notch Geometry on Mode Ratio (KII/KI) under Mixed Mode (I + II) Loading
احسان براتیIn inclined U-notches, the mixed mode (I + II) loading occurs and the mode ratio can be increased by varying the notch angle. In this paper, the effect of the inclined U-notch geometry, i.e. the notch depth, the notch angle, the notch root radius, and the position of th أکثرIn inclined U-notches, the mixed mode (I + II) loading occurs and the mode ratio can be increased by varying the notch angle. In this paper, the effect of the inclined U-notch geometry, i.e. the notch depth, the notch angle, the notch root radius, and the position of the notch with respect to supports, on the mode ratio (KII/KI) have been studied. Three-point bending and plane strain condition have been considered in this study. Finite element results using ANSYS have shown that the mode ratio increases by increasing the notch root radius. Also, it has been found that the mode ratio decreases by increasing the distance of the notch from the supports, and by increasing the notch angle. However, it is seen that the notch depth has complicated effect on the mode ratio. The variation of the mode ratio with respect to the notch depth has a relative maximum and a relative minimum. تفاصيل المقالة -
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275 - An Initiative Plan of the Equivalent Model for Simulation of theWelding Process
علی حیدری محمدرضا فروزان جعفر گلستانهMany researchers content themselves with the 2D simulation of welding process instead of the 3D simulation, because of the time and the cost factors of the latter. In this research, the number of elements and nodes are reduced by an initiative plan (defining an equivale أکثرMany researchers content themselves with the 2D simulation of welding process instead of the 3D simulation, because of the time and the cost factors of the latter. In this research, the number of elements and nodes are reduced by an initiative plan (defining an equivalent model) for the simulation of welding. The welding process has been simulated by an uncoupled thermal-mechanical finite element model in three steps. Thermal history was determined from thermal analysis, and then the distribution of the metallurgical phase on the fusion and heat affected zones were calculated by a certain code. Afterward, the stress distribution was computed from mechanical analysis, where the material property was defined element by element according to the second step. One of the most important objectives of this simulation is to study the residual stresses of welding. Comparisons between the thermal analysis results and the metallographic and laboratory results of this research show acceptable accuracy of the proposed method. تفاصيل المقالة -
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276 - Prediction of Fatigue Life in Notched Specimens Using Multiaxial Fatigue Criteria
فیروز اسماعیلی گلدرق سجاد برزگر محمدی علیرضا بابائی امیر افکارIn this research, the effects of notch shape on the fatigue strength of 2024-T3 aluminum alloy notched specimens have been studied using experimental and multiaxial fatigue analysis. For this purpose, four set of specimens with different notch shape were prepared and th أکثرIn this research, the effects of notch shape on the fatigue strength of 2024-T3 aluminum alloy notched specimens have been studied using experimental and multiaxial fatigue analysis. For this purpose, four set of specimens with different notch shape were prepared and then fatigue tests were carried out at various cyclic longitudinal load levels. Load controlled fatigue tests of mentioned specimens have been conducted on a 250kN servo-hydraulic Amsler H250 fatigue testing machine with the frequency of 10Hz. A nonlinear finite element ANSYS code was used to obtain stress and strain distribution in the specimens due to the longitudinal applied loads for all kinds of specimens. Estimation fatigue lives of the specimens were carried out with several different multiaxial fatigue criteria by means of local stress and strain distribution obtained from finite element analysis, i.e. KBM, FS, Crossland, VF and WY, by means of local stress and strain values obtained from finite element simulations. Results obtained from the multiaxial analysis revealed that among the applied criteria, the Crossland’s criterion has the best accuracy for all types of the specimens. تفاصيل المقالة -
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277 - Analysis of Roll Wear in Reshaping Using Finite Element Simulation
مهدی سلمانی تهرانی رضا خدابنده شهرکی حسام ولیدیReshaping process is a widely used method for producing tubes with non-circular cross sections. Owing to the friction between pipe and rolls, initial round pipe moves forward and consequently, it gradually formed into square or rectangular one. In practice, geometric pr أکثرReshaping process is a widely used method for producing tubes with non-circular cross sections. Owing to the friction between pipe and rolls, initial round pipe moves forward and consequently, it gradually formed into square or rectangular one. In practice, geometric profile of the rolls will be changed after a while. These changes would be detrimental the production of faultless products. Therefore, in this paper the reshaping process is studied considering wear phenomena on the rolls. This study is a co-operation with a related industry at which square tubes are produced using reshaping process. In order to investigate the production line, considering industrial datasheets, the process is modeled by means of a commercial FEM package, ABAQUS\Explicit. The reshaping process is simulated as a 3D model and subsequently the sustainable regions to wear are investigated. The influences of significant parameters such as material and thickness of strip, as well as friction coefficient on the worn area, are studied. At the end, the FEM reults are comprised with the experiments reults and a good consistency between them is seen. تفاصيل المقالة -
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278 - Experimental and Numerical Study of Preform Design in Multi Stage Deep Drawing of High Strength Thin Steel Sheet
اکبر زمانی علیشاه مهدی تاجداری جعفر اسکندری جم جمال صیدیIn this paper, experimental results of a deep drawing processto produce a cylinder of high strength steel with a spherical head were compared with it’s simulation results and three proposal design types. Meanwhile, the amount of limiting draw ratio in some stages أکثرIn this paper, experimental results of a deep drawing processto produce a cylinder of high strength steel with a spherical head were compared with it’s simulation results and three proposal design types. Meanwhile, the amount of limiting draw ratio in some stages was determined. Accuracy and precision of the results of a finite element software to predicting the multi stage deep drawing process of high-strength thin steel sheets was measured. ABAQUS version 6-9-3 was used to simulate the process. In this research, the raw material was a circular blank of annealed steel AISI-4130 with 2 mm thickness that in experimental test, subjected to one drawing stages, three redrawing stage and two heat treatment stages. The uni-axial tensile test was performed to determine the mechanical properties of the steel sheet. Numerical thickness distribution was compared with the experimental results in different stages of deep drawing and the accuracy was good (about 2.55%). Base on this results the proposal designs were simulated to introduce the properties of the most suitable design types. تفاصيل المقالة -
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279 - Numerical Investigations on the Effect of Pulsating Pressure on Improvement of Formability in Hydroforming of Bent Tube by FEM
امیر خورسندی محسن لوح موسویIn this paper, hydroforming process of bent tubes in T-shaped die is studied for pulsating and linear pressure paths by the finite element method. Forming Limit Diagrams (FLDs) and thickness distribution curves are used to investigate the effect of pulsating pressure on أکثرIn this paper, hydroforming process of bent tubes in T-shaped die is studied for pulsating and linear pressure paths by the finite element method. Forming Limit Diagrams (FLDs) and thickness distribution curves are used to investigate the effect of pulsating pressure on hydroforming process. In addition, the obtained numerical results are compared with experimental results of hydroforming of straight tubes with T-shape protrusions. Itis shown that for tubes with similar bend radius and diameter of bent tube, the formability increases by linear pressure which means pulsating pressure is not so effective. But in the bent tubes whith bend radius larger than tube diameter, pulsating pressure improves formability in hydroforming process. Also, it is found that in hydroforming the pulsating pressure can not increase formability in any bent tube case. In some cases the linear pressure path is more effective for formability. تفاصيل المقالة -
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280 - Presentation and Analysis of Methods for Increasing Glue Joint Strength in the Same Length Joint
A.H. Ehsani Ehsani M. Shirzadian Gilan A. Ghafori Sayad A. Shokrgozar NaviGlue joints are more useful in Aerospace so in this article we presented new method for glue joint. In this method the maximum stresses that occurs at the edges of the bottom glue joint and cause ultimate failure in this type of connection is Decrease and increase the g أکثرGlue joints are more useful in Aerospace so in this article we presented new method for glue joint. In this method the maximum stresses that occurs at the edges of the bottom glue joint and cause ultimate failure in this type of connection is Decrease and increase the glue joint strength. In this method glue in the area overlapping the discrete and separate column considered Also, the connection is assumed to be identical for the proposed method. As a result, in this case less glue is used for connection. At first the proposed method has been studied to offer and distribute the tension in the glue is analyzed then modeling glue joints for common conditions and proposed with use of the finite element software for numerical analysis تفاصيل المقالة -
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281 - Inverse Identification of Circular Cavity in a 2D Object via Boundary Temperature Measurements Using Artificial Neural Network
محمد امین احمدفرد محمد جواد کاظم زاده پارسی علیرضا تهورIn geometric inverse problems, it is assumed that some parts of domain boundaries are not accessible and geometric shape and dimensions of these parts cannot be measured directly. The aim of inverse geometry problems is to approximate the unknown boundary shape by condu أکثرIn geometric inverse problems, it is assumed that some parts of domain boundaries are not accessible and geometric shape and dimensions of these parts cannot be measured directly. The aim of inverse geometry problems is to approximate the unknown boundary shape by conducting some experimental measurements on accessible surfaces. In the present paper, the artificial neural network is used to solve these kinds of problems in conduction heat transfer in 2D objects. In order to train the neural network, some direct problems are solved by using the finite element method. In order to evaluate the applicability of the proposed method, different cases with different number of measuring points and different error levels are examined. The results show that the ANN can effectively be used in solving inverse geometry problems in heat conduction. تفاصيل المقالة -
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282 - Study of Aspect Ratio Effect on Mechanical Properties Polymer/NanoComposite
محمد هاشمی گهروئی حسین گلستانیان مهدی سلمانی تهرانیCarbon nanotubes (CNTs) demonstrate unusually high stiffness, strength and resilience, and are therefore an ideal reinforcing material for nanocomposites. However, much work has to be done before the potentials of CNT-based composites can be fully realized. Evaluating t أکثرCarbon nanotubes (CNTs) demonstrate unusually high stiffness, strength and resilience, and are therefore an ideal reinforcing material for nanocomposites. However, much work has to be done before the potentials of CNT-based composites can be fully realized. Evaluating the effective material properties of such nanoscale materials is a very difficult tasks. Simulations using molecular dynamics and continuum mechanics models can play significant roles in this development. Currently, the continuum approach seems to be the only feasible approach for such large scale analysis. In this paper, effective mechanical properties of CNT-based composites are evaluated using a square representative volume element (RVE) based on the continuum mechanics and Finite Element Method (FEM). Formulas are derived based on the elasticity theory to extract the effective material constants from solutions for the square RVEs under two load cases. Next, CNT aspect ratio effects on the nanocomposite mechanical properties are investigated. Results indicate that increasing CNT aspect ratio results in an increase in nanocomposite longitudinal modulus and a decrease in nanocomposite transverse modulus. Also, increasing the CNT aspect ratio resulted in a decrease in nanocomposite Poisson’s ratio in the x-y plane and an increase in nanocomposite Poisson’s ratio in the x-z plane. تفاصيل المقالة -
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283 - Low-speed impact behavior of two-layer similar and dissimilar metal laminate structures
هادی خرّمی شاد محمد باقری توفیقیMechanical behavior of two-layer metal laminate structures under low-speed impact loading was investigated experimentally and numerically. The experimental results were just used for validation of numerical results. Then numerical modeling was used to study the behavior أکثرMechanical behavior of two-layer metal laminate structures under low-speed impact loading was investigated experimentally and numerically. The experimental results were just used for validation of numerical results. Then numerical modeling was used to study the behavior of metal laminates in details. The mechanical behavior of the metal laminate structures under impact loading was found to be dependent on the material substance of the layers. The metal layers were made of four common materials used in the industry. Results showed that the maximum amount of contact force and minimum amount of contact duration for the metal laminate structures with similar metal layers were obtained when the layers were made of steel. Whereas, the maximum amount of displacement and dissipated energy were achieved for the structure with lead layers. For the structures in which the first metal layer was Al-6061T6, the maximum contact force obtained when the second metal layer was made of steel; and the maximum displacement occurred when the second metal layer was made of lead. It was found that the maximum mean amount of contact force belonged to the structures with first metal layer of steel and the maximum mean amount of displacement belonged to the structures with the first metal layer of lead. The finite element analysis results were in good agreement with the experimental results and also with the other researcher’s results. تفاصيل المقالة -
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284 - Axial Crushing Analysis of Sandwich Thin-walled Tubes using Experimental and Finite Element Simulation
سجاد آذرخش عباس رهیApplication of impact energy absorption systems in different industries is of special significance. Thin-walled tubes, due to their lightness, high energy absorption capacity, long crushing length and the high ratio of energy absorption to weight, have found ever-increa أکثرApplication of impact energy absorption systems in different industries is of special significance. Thin-walled tubes, due to their lightness, high energy absorption capacity, long crushing length and the high ratio of energy absorption to weight, have found ever-increasing application as one of the most effective energy absorption systems. In this research, through carrying out experimental tests and finite element simulation, the crushing mechanism of hollow & solid (filled with polyurethane foam), sandwiched, thin-walled structures under the influence of axial, quasi-static loading has been studied. The tested cylindrical samples are made using extrusion method. These samples are compressed between two rigid plates under quasi-static loading conditions, and then the collapse mechanism, the crushing force fluctuations and absorbed energy are determined. A numerical model is presented based on the finite element analysis to simulate the collapse process, considering the non-linear responses of material behavior, contact surface and large deformation effects. Simulation of tested specimen has been executed by ABAQUS software in 3- dimensional models through explicit method. Comparison of numerical and experimental results showed that the present model provided an appropriate procedure to determine the collapse mechanism, crushing load and the amount of energy absorption. The model is used to evaluate the thickness effects of the tube, material quality, imperfection and density of the foam on the mean crush load, energy absorption capacity, and collapse mechanism of cylindrical shells. Research results showed that the existence of foam increases the amount of energy absorbtion in the structures. Increase of energy absorbtion and also increase of average crushing force, in foams with higher density is more evident. تفاصيل المقالة -
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285 - Elastic Buckling Analysis of Composite Shells with Elliptical Cross-section under Axial Compression
منصور درویزه ابوالفضل درویزه رضا انصاری الهام کاظمیIn the present research, the elastic buckling of composite cross-ply elliptical cylindrical shells under axial compression is studied through finite element approach. The formulation is based on shear deformation theory and the serendipity quadrilateral eight-node eleme أکثرIn the present research, the elastic buckling of composite cross-ply elliptical cylindrical shells under axial compression is studied through finite element approach. The formulation is based on shear deformation theory and the serendipity quadrilateral eight-node element is used to study the elastic behavior of elliptical cylindrical shells. The strain-displacement relations are accurately accounted for in the formulation in local coordinate system. The contributions of the work done by applied load are also incorporated. The obtained governing equations by the principle of minimum potential energy is solved through eigenvalue approach. The influence of elliptical cross-sectional parameters on the critical buckling loads of elliptical cylindrical shells is examined .Results show that changes in the elliptical cross-sectional parameters significantly change critical buckling loads of the elliptical cylindrical shells. تفاصيل المقالة -
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286 - Study of the Effects of Lacing Rods Location on Natural Frequencies in Last Stage Blades of a Steam Turbine
مهدی نوذرپور عباس رهیIn this study, effects of lacing rods location on natural frequencies of last stage of a Steam Turbine Blades (STBs) have been investigated. STBs are critical and important elements in a turbine as well as power plants. One of the most important parameters in turbine bl أکثرIn this study, effects of lacing rods location on natural frequencies of last stage of a Steam Turbine Blades (STBs) have been investigated. STBs are critical and important elements in a turbine as well as power plants. One of the most important parameters in turbine blades is lacing rods location. In this paper, first, a three dimensional (3D) scan was used to produce the geometrical model of the blade. Then, last stage of a low pressure turbine have been produced and simulated by assembling of the one-blade model. There are two rows of lacing rods in the last stage of turbine. In this paper, effecting the lacing rods location on natural frequencies of system has been studied. According to the Campbell diagrams, the results showed there is no resonance in the last stage blades of the steam turbine for different locations of the lacing rods. تفاصيل المقالة -
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287 - A Roll Wear Prediction Model in Hot Plate Rolling
امیر نورانی محمود سلیمیIn this paper, the wear of work roll in hot plate rolling is introduced and the parameters affecting wear mechanisms in hot strip mill are investigated. In addition, different wear mechanisms in hot rolling and the differences between these mechanisms in different stand أکثرIn this paper, the wear of work roll in hot plate rolling is introduced and the parameters affecting wear mechanisms in hot strip mill are investigated. In addition, different wear mechanisms in hot rolling and the differences between these mechanisms in different stands are explained. Using the finite element method and the rolling equations, a work roll wear model is proposed. Wear is modeled using the resultant pressure distribution along the roll barrel. To obtain the tentative coefficient, summation of wear in each pass schedule is obtained and calibrated via actual wear of samples tested in the Mobarakeh Steel Company. Finally, the theoretical wear values are compared with those of the experiment. The predicted wear profiles are found to be in good agreement with those of the experimental measured values. تفاصيل المقالة -
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288 - Propagation of Crack in Linear Elastic Materials with Considering Crack Path Correction Factor
مهران مرادی مهدی پورمحمودModeling of crack propagation by a finite element method under mixed mode conditions is of prime importance in the fracture mechanics. This article describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture me أکثرModeling of crack propagation by a finite element method under mixed mode conditions is of prime importance in the fracture mechanics. This article describes an application of finite element method to the analysis of mixed mode crack growth in linear elastic fracture mechanics. Crack - growth process is simulated by an incremental crack-extension analysis based on the maximum principal stress criterion which is expressed in terms of the stress intensity factor. In this paper a procedure is employed to correct direction of crack propagation to ensure that a unique final crack path is achieved for different analysis of a problem by using different increments of crack. For each increment of crack extension, finite element method is applied to perform a single - region stress analysis of the cracked structure. Results of this incremental crack – extension analysis are presented for several geometries. تفاصيل المقالة -
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289 - Nonlinear Finite Element Analysis of Thermoelastic Stresses of FGM Rotating Disk Considering Temperature-Dependency of Material Properties
مهرنوش دمیرچلی محمد آزادیIn the present paper, nonlinear radial and hoop thermoelastic stresses analysis of a disk made of FGMs material is investigated. According to this purpose, finite element method is used. In the present method, second-order one-dimensional element (with three node points أکثرIn the present paper, nonlinear radial and hoop thermoelastic stresses analysis of a disk made of FGMs material is investigated. According to this purpose, finite element method is used. In the present method, second-order one-dimensional element (with three node points) is proposed. The geometrical and stress boundary conditions are defined in the state of non-existence of external pressure and then zero radial stress in the outer layer of the disk, and zero displacement in the center of the disk. Also the temperature distribution is assumed as linear. The material properties changes including temperature-dependency are modeled. Finally, a numerical example is proposed to show the radial displacements, radial and hoop thermoelastic stresses versus radius of the disk for different power (N) from Power-law and different angular velocities. The results show that by increasing both two parameters, N and angular velocity of the disk, the amounts of displacement and stress are increased. At last, temperature-dependency and temperature-independency of material properties is investigated. تفاصيل المقالة -
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290 - A Comparative Study Between Analytical, Finite Element Method andthe Experimental Results in Wire Drawing of Copper
محمد احمدپور حسن خادمی‌زادهThe wire drawing process is extensively used in manufacturing components such as rivet, screw, welding wire, etc. In this work, an analytical of the wire drawing process has been considered for two-stage operation. ABAQUS commercial Finite Element code has been used to أکثرThe wire drawing process is extensively used in manufacturing components such as rivet, screw, welding wire, etc. In this work, an analytical of the wire drawing process has been considered for two-stage operation. ABAQUS commercial Finite Element code has been used to obtained the drawing force. Then, The analytical and experimental results been compared. The results show a good agreement for copper. تفاصيل المقالة -
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291 - Numerical and Experimental Analysis of Forming Rectangular Copper Pipes by Successive Rolling of Round Pipe Filled With Bismuth
علی بصیرت نیا محسن لوح موسویBecause of their wide application in industries requiring high pressure and temperature, manufacturing square and rectangular pipes have attracted more attention than ever before.There are various methods such as extrusion, tensile and stress for manufacturing square pi أکثرBecause of their wide application in industries requiring high pressure and temperature, manufacturing square and rectangular pipes have attracted more attention than ever before.There are various methods such as extrusion, tensile and stress for manufacturing square pipes. Another method on which studies have focused in recent years is the re-forming of round pipes in order to turn them into square or rectangular ones. The methods suggested in these researches are all applicable for the manufacture of square pipes without the possibility of manufacturing rectangular pipes. The method introduced in this paper consists of filling the pipe with bismuth and rolling it in three successive stages. In this research, first, the intended process is simulated in Abaqus software, and then a real sample is manufactured by an experimental test. The manufactured sample is checked with regard to its dimensions and is compared with the results obtained from the simulation. The results of the study show that the method of filling the pipe with bismuth and moving it through three rollers is an appropriate method for the manufacture of thin-walled pipes with rectangular cross-section. تفاصيل المقالة -
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292 - Optimization of Axisymmetric Extrusion Die Profiles
حسن نحوی مهدی حسن زادهIn this research, optimization process of axisymmetric extrusion dies is proposed. Plastic zone is analyzed using finite element method in the Eulerian system with flow formulation. The die profiles are defined by Bezier curves with six control points. Two effective fun أکثرIn this research, optimization process of axisymmetric extrusion dies is proposed. Plastic zone is analyzed using finite element method in the Eulerian system with flow formulation. The die profiles are defined by Bezier curves with six control points. Two effective functions are considered in this research; standard deviation of the strain rate and the rate of energy consumption during extrusion process. A coupled numerical approach of finite element analysis in Eulerian system and the non-gradient Nelder-Mead method is utilized to determine optimum die profiles. Results show that optimized die has higher uniformity in strain rate distribution and less strain values with respect to the non-optimum conical die. In the case of minimizing energy consumption rate, results show that for the die with constant and variable lengths and low friction, the die profile tends to the stream line. In die with variable length and high friction, friction has more effective role in optimization and the die length tends towards lower lengths during optimization. تفاصيل المقالة -
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293 - Static and Dynamic Analysis of Bus Structure and Chassis of O-457
ابوالفضل محبوبی شاد محسن اصفهانیانWith due attention to the fact that the local and foreign vehicle industries are changing and modifying the previous designs in order to produce new designs, the components of self-propelled are to be differently analyzed. Static and dynamic analysis is one of them. In أکثرWith due attention to the fact that the local and foreign vehicle industries are changing and modifying the previous designs in order to produce new designs, the components of self-propelled are to be differently analyzed. Static and dynamic analysis is one of them. In this paper, chassis and body of a o-457 bus were studied and analyzed under finite element method (using ANSYS).This process was begun with three dimensional modeling of suspension system, chassis and structure of bus. At first, as an initial stage, a static analysis was performed on the bus to assure the resistance of its chassis. In the next stage, the dynamic analyzed including modal and transient analyses were carried out. In the transient analysis, the symmetric and asymmetric simulations were done in order to test structural resistance and flexibility of the bus. تفاصيل المقالة -
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294 - Numerical Study on Effect of Bilinear Pressure Path on Corner Filling in Hydroforming of Tube in Box-Shape Die
محسن لوح موسوی میثم شهبازیDie corner filling is very important in tube hydroforming process. Definition of the internal pressure path is a key factor in improving the corner filling. However, the factors that cause improvement of corner filling are still unclear. In this paper, effect of bilinea أکثرDie corner filling is very important in tube hydroforming process. Definition of the internal pressure path is a key factor in improving the corner filling. However, the factors that cause improvement of corner filling are still unclear. In this paper, effect of bilinear pressure path on corner filling in hydroforming of tube in box-shape die is studied using both finite element simulation and experiment. For this pressure path, pressure increases to an initial pressure and then it increases to a final pressure (calibration pressure) linearly. It is shown that, an initial pressure lower than yield pressure of the tube is caused a small wrinkle which is eliminated into the corner of die and thus the corner filling is improved, whereas for other pressure paths with higher initial pressures a round bulging occurred in former stages of deformation, and thus the corner filling of die is deteriorated. تفاصيل المقالة -
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295 - Numerical and Experimental Investigation of Cold orBital Forging of a 16MnCr5 Alloy Spur Bevel Gear
سعید بهشتیان مسگران محمد علی صادقیThe purpose of this research is to analyze the forging of bevel gears based on conventional forging method with material number 1.7131 with finite element method by means of SUPER FORGE software and to compare it with experimental cold orbital forging results.After doin أکثرThe purpose of this research is to analyze the forging of bevel gears based on conventional forging method with material number 1.7131 with finite element method by means of SUPER FORGE software and to compare it with experimental cold orbital forging results.After doing simulation of conventional forging and obtaining press tonnage due to orbital forging method with DEFORM software, orbital forging dies are produced. Since bevel gears production based on conventional forging has three pre-form steps, so the forging process should be applied on the basis of hot forge. But in orbital forging process, bevel gear is produced in only one step which is cold forge. Finally, a comparison is done between microstructure of bevel gear which is produced by orbital forging and a bevel gear that is constructed through machining method and dies. Results obtained showed that the method of pieces production just before applying the heat treatment process have a high effectiveness on the microstructure. In orbital forging the tonnage of the levels are lower than conventional forging method and the capability of filling the mold’s cavity of raw materials in orbital forging is more than conventional forging method. The geometry of the billet have more affect on filling the mold’s cavity. تفاصيل المقالة -
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296 - Analysis of Fatigue Cracks of Diesel Engines Cylinder Heads using a Two-Layer Viscoplasticity Model and Considering Viscousity Effects
حجت عاشوری بابک بهشتی محمد رضا ابراهیم زادهLoading conditions and complex geometry have led the cylinder heads to become the most challenging parts of diesel engines. One of the most important durability problems in diesel engines is due to the cracks valves bridge area. The purpose of this study is a thermo-mec أکثرLoading conditions and complex geometry have led the cylinder heads to become the most challenging parts of diesel engines. One of the most important durability problems in diesel engines is due to the cracks valves bridge area. The purpose of this study is a thermo-mechanical analysis of cylinder heads of diesel engines using a two-layer viscoplasticity model. The results of the thermo-mechanical analysis indicate that the maximum temperature and stress exist in the valves bridge. The results of the finite element analysis correspond with the experimental tests, carried out in references, and illustrate the cylinder heads cracked in this region. The results of the thermo-mechanical analysis show that when the engine is running the stress in the region is compressive caused by the thermal loading and combustion pressure. When the engine shuts off the compressive stress turns into the tensile stress because of assembly loads. The valves bridge is under the cyclic tensile and compressive stress and then is under low-cycle fatigue. After several cycles the fatigue cracks will appear in this region. The lifetime of this part can be determined through finite element analysis instead of experimental tests. Viscous strain is more than the plastic strain which is not negligible تفاصيل المقالة -
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297 - Numerical Simulation of Impact of Low Velocity Projectiles With Water Surface
نجمه خضرائیان ناصر دشتیان گرامیIn this article, Finite Element Method (FEM) and Eulerian-Lagrangies Algorithm (ELA) formulation were used to numerically simulate the impact of several low-velocity projectiles with water surface. Material models which were used to express behavior of air and water inc أکثرIn this article, Finite Element Method (FEM) and Eulerian-Lagrangies Algorithm (ELA) formulation were used to numerically simulate the impact of several low-velocity projectiles with water surface. Material models which were used to express behavior of air and water included Null material model. For the projectiles, rigid material model were applied. Results were validated by analyzing the impact of metallic cylinder with a water surface and then the impact of a wedge, sphere and special projectile at low-velocities were simulated. Major outputs were force and pressure applied to the projectile, variations of velocity and acceleration when entering to the water, stress-strain variations and variations of water surface in various steps of the analysis. Results showed that the impact of the structure with fluid can be modeled using finite element model with high accuracy in terms of quality and quantity.Numerical results obtained for cylinder well agrees with the available experimental data. Also the results for other projectiles show a logical trend تفاصيل المقالة -
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298 - Experimental Study of the Voltage and Number of the Coil Rounds in Electromagnetic Forming Process of the V shape Aluminum sheets
سجاد نادیان برسیانی احمد کشاورزی امین کلاه دوزElectromagnetic power, which is one of the fast ways for forming, is used for forming workpieces without having any effect on them. Using it causes the workpieces to reach the minimum back spring and tear; consequently building the equipment like pistons will cost less أکثرElectromagnetic power, which is one of the fast ways for forming, is used for forming workpieces without having any effect on them. Using it causes the workpieces to reach the minimum back spring and tear; consequently building the equipment like pistons will cost less than before. Electromagnetic power is used for forming Aluminium sheets into V shapes in this study. As the coils connect the machine and the workpieces, the number of rounds and the voltage in 10 levels will be discussed in this study. Considering the results and analysis that have been reached, the best forming occurs in the voltage of 1500 and 35 rounds. Because the machine creates a high ampere and a proper amount of rounds in this voltage in order to transfer the whole power to the workpiece. As the rounds increase to 40, the forming will decrease up to 34/3 percent تفاصيل المقالة -
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299 - پیشبینی پارامترهای چسبندگی الیاف فولادی هوک شکل و بتن با استفاده از شبکه‌های عصبی مصنوعی
امیر ابراهیم اکبری بقالبا توجه به اهمیت بکارگیری الیاف فولادی در تقویت بتن، در تحقیق حاضر با استفاده از شبکه‌های عصبی مصنوعی به پیشبینی رفتار بیرون کشیدگی الیاف فولادی هوک شکل از بتن پرداخته شده است. به دلیل محدودیت داده‌های جامع آزمایشگاهی، از داده‌های به دست آمده از تحلیل المان محدود به عن أکثربا توجه به اهمیت بکارگیری الیاف فولادی در تقویت بتن، در تحقیق حاضر با استفاده از شبکه‌های عصبی مصنوعی به پیشبینی رفتار بیرون کشیدگی الیاف فولادی هوک شکل از بتن پرداخته شده است. به دلیل محدودیت داده‌های جامع آزمایشگاهی، از داده‌های به دست آمده از تحلیل المان محدود به عنوان ورودی شبکه عصبی استفاده شده است. به منظور شبیه‌سازی بیرون کشیدگی الیاف از روش المان محدود سه‌بعدی و نرم‌افزار آباکوس استفاده می‌شود. در مدل المان محدود، اندرکنش بین الیاف و بتن با استفاده از مفهوم ناحیه انتقالی سطح مشترک شبیه‌سازی شده است که پارامترهای آن با استفاده از روش المان محدود معکوس و استفاده از نتایج تست تجربی بیرون‌کشیدگی انجام پذیرفته بر روی یک نمونه الیاف به دست آمده است. پس از صحت‌سنجی نتایج مدل عددی با نتایج تجربی، نتایج به ازای پارامترهای مؤثر الیاف استخراج شده و بر اساس آنها مدلسازی با استفاده از شبکه‌های عصبی صورت گرفته است. پیشبینی نیروی بیرون‌کشیدگی توسط شبکه‌های عصبی مصنوعی چندلایه و الگوریتم آموزش انتشار به عقب، با تکنیک بهینه‌سازی مارکورادت-لونبرگ انجام شده است. نتایج نشان می‌دهد که مدل شبکه عصبی ارائه شده در این تحقیق، به دلیل توانایی استفاده از متغیرهای بیشتر در مدلسازی و نتایج دقیق‌تر، روشی مؤثر برای پیشبینی نیروی بیرون‌کشیدگی الیاف از بتن است. تفاصيل المقالة -
حرية الوصول المقاله
300 - تشخیص خسارت در پل‌های بزرگ دهانه با وجود چند خسارت همزمان
محمد وحیدی آرمین عطیمی نژاد مریم فیروزی محمد هریسچیانمقاله حاضر یک روش دومرحله‌ای قدرتمند برای تشخیص خسارت پل‌های بزرگ دهانه با مقاطع متغیر ارائه می‌نماید. پل‌ها یکی از زیرساخت‌های اساسی در حوزه حمل‌ونقل شهری و برون شهری بوده که تشخیص خسارت به موقع درطول بهره‌برداری آن حائز اهمیت میباشد. خسارت دراین دسته از سازه‌ها سبب ا أکثرمقاله حاضر یک روش دومرحله‌ای قدرتمند برای تشخیص خسارت پل‌های بزرگ دهانه با مقاطع متغیر ارائه می‌نماید. پل‌ها یکی از زیرساخت‌های اساسی در حوزه حمل‌ونقل شهری و برون شهری بوده که تشخیص خسارت به موقع درطول بهره‌برداری آن حائز اهمیت میباشد. خسارت دراین دسته از سازه‌ها سبب اختلال درخدمت‌رسانی درزمان بروزبلایای طبیعی‌خواهد شد. روش ارائه شده بر مبنای ترکیب المان محدود طیفی و شاخص خسارت انرژی کرنشی مودال و همچنین ترکیب الگوریتم ژنتیک و رگرسیون بردار پشتیبان برای تشخیص وتخمین میزان شدت‌خسارت میباشد. یکی از روشهای کارآمد درحوزه انتشار امواج روش المان محدود طیفی بوده که از قابلیت مدلسازی با انعطاف‌پذیری بالا و تشخیص خسارات ریز میباشد. روشهای مبتنی بر ارتعاش بطور گسترده برای تشخیص خسارت سازه‌ها استفاده میگردد درحالیکه شاخص خسارت انرژی کرنشی مودال از حساسیت بالاتری در تشخیص خسارت در میان دیگر روشهای مبتنی برارتعاش برخوردار است. مدل مورد تحقیق، پل‌کروچایلد درغرب کانادا میباشد که دارای ویژگی‌های خاصی از نظرهندسی و هم از مشخصات المان‌های سازه‌ای میباشد. در این تحقیق شاخص خسارت انرژی کرنشی مودال به علت تغییر مقطع در طول شاه‌تیر‌ها اصلاح گردیده است. همچنین از رگرسیون بردار پشتیبان به عنوان یک تکنیک قدرتمند در تخمین میزان شدت خسارت استفاده شده است. جهت افزایش دقت و بهبود روش تخمین میزان شدت خسارات از الگوریتم ژنتیک برای بهینه‌سازی پارامترهای مؤثر رگرسیون بردار پشتیبان استفاده میگردد. روش ترکیبی الگوریتم ژنتیک و رگرسیون بردار پشتیبان توانسته است به نحو مطلوبی شدت خسارات را تخمین بزند. تفاصيل المقالة
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