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دسترسی آزاد مقاله
1 - نتایجی در مورد مدول‌های k- بی‌تاب
مریم سلیمیفرض کنید R یک حلقه جابه‌جایی و نوتری باشد. در ، مدول‌های بی‌تاب به‌عنوان تعمیمی از مدول‌های بی‌تاب و انعکاسی تعریف شده‌اند. بدین معنا که مدول‌های بی‌تاب، مدول 1- بی‌تاب و مدول‌های انعکاسی، مدول 2- بی‌تاب باشند. در این مقاله، برخی از ویژگی‌های مدول‌های بی‌تاب، انعک چکیده کاملفرض کنید R یک حلقه جابه‌جایی و نوتری باشد. در ، مدول‌های بی‌تاب به‌عنوان تعمیمی از مدول‌های بی‌تاب و انعکاسی تعریف شده‌اند. بدین معنا که مدول‌های بی‌تاب، مدول 1- بی‌تاب و مدول‌های انعکاسی، مدول 2- بی‌تاب باشند. در این مقاله، برخی از ویژگی‌های مدول‌های بی‌تاب، انعکاسی و در حالت کلی بی‌تاب را مورد بررسی قرار می‌دهیم. ثابت می‌کنیم که برای مدول با فرض ، مدول بی‌تاب است اگر و تنها اگر برای هر ، به طوری‌که ، مدول بی‌تاب باشد، و برای هر به طوری‌که داشته باشیم . بعلاوه، با استفاده از فرمول آسلندر - بریدجر، ثابت می‌کنیم مدول بی‌تاب است اگر و تنها اگر برای هر ، به طوری‌که ، مدول بی‌تاب باشد، و برای هر به طوری‌که داشته باشیم . همچنین ثابت می‌کنیم که روی حلقه‌های گورنشتاین و موضعی با بعد ، کلاس مدول‌های ماکزیمال کوهن - مکالی و کلاس مدول‌های بی‌تاب معادلند. در پایان شرایط لازم و کافی برای این که حاصل‌ضرب تانسوری مدول‌های بی‌تاب مدول بی‌تاب شود را به‌دست می‌آوریم. پرونده مقاله -
دسترسی آزاد مقاله
2 - Modifications of Internal Molecular Structures of Asphalt Components Due to Physical Aging
Iffat R. ArisaThe internal structure of a molecule can be presented in terms of intra-molecular (i.e., inter atomic)and inter-molecular energies such as van der Waals, bond and bending, torsion, and inversion energy.In this study, changes in molecular energies of individual asphalt c چکیده کاملThe internal structure of a molecule can be presented in terms of intra-molecular (i.e., inter atomic)and inter-molecular energies such as van der Waals, bond and bending, torsion, and inversion energy.In this study, changes in molecular energies of individual asphalt components are evaluated as afunction of physical aging factors. The factors for physical aging such as temperature and pressureare considered in a molecular dynamics simulation framework. The simulations are carried out byvarying temperatures within the range from -35 ºC to 75 ºC and pressures within the range from 0.95atm to 1.1 atm. The outputs of the simulations give a clear idea about the internal structure ofmolecules in liquid state. Simulation results show that physical aging process causes increase in bondstretching, angle bending, and torsion energy. Application of high temperatures results in highstretching of asphalt atoms. At high temperature intermolecular van der Waals repulsion increases.Pressure variation has negligible effects on intra and inter-molecular energy changes. From inversionenergy values, the geometry of the molecules is found. پرونده مقاله -
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3 - Planarity of Intersection Graph of submodules of a Module
P. MalakootiLet $R$ be a commutative ring with identity and $M$ be an unitary $R$-module. The intersection graph of an $R$-module $M$, denoted by $\Gamma(M)$, is a simple graph whose vertices are all non-trivial submodules of $M$ and two distinct vertices $N_1$ and $N_2$ are adjace چکیده کاملLet $R$ be a commutative ring with identity and $M$ be an unitary $R$-module. The intersection graph of an $R$-module $M$, denoted by $\Gamma(M)$, is a simple graph whose vertices are all non-trivial submodules of $M$ and two distinct vertices $N_1$ and $N_2$ are adjacent if and only if $N_1\cap N_2\neq 0$. In this article, we investigate the concept of a planar intersection graph and maximal submodules of an $R$-module. In particular, we show that if $\Gamma(M)$ is a planar graph, then $M\cong M_1\oplus M_2$ for a multiplication $R$-module $M$ with $|Max(M)|\neq 1$‎.‎ پرونده مقاله -
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4 - Optimal Design of Steppers in Single Step High Pressure Torsion (SIHPT) Process as a Novel SPD Method
Mehdi Eskandarzadeh Ghader Faraji A. Masoumi Ali KalakiSingle Step High Pressure Torsion (SIHPT) is a newly developed HPT based method for processing of materials which is capable of producing nanostructured long samples with characteristics comparable to conventional HPT process. While, conventional HPT can be applied only چکیده کاملSingle Step High Pressure Torsion (SIHPT) is a newly developed HPT based method for processing of materials which is capable of producing nanostructured long samples with characteristics comparable to conventional HPT process. While, conventional HPT can be applied only on thin samples; it is possible to produce nanostructured parts with about 10 cm long using SIHPT method. However, SIHPT needs some technical improvements in order to be used for production in industrial scale. One of key component of SIHPT is the steppers which help different sections of the sample to be twisted. This study investigates main parameters of Steppers including the corner radius, thickness and rotation speed. The experimental results revealed that for the lowest length of sample’s contact inside the Steppers (lower contact length) of 5mm; there is considerable slippage in pressures below 1GP. However, the amount of slippage decreases gradually by increasing the magnitude of the applied pressure and the amount of the lower contact length. Moreover, it found that the rotational speed influences the amount of slippage in low pressures (lower than 1 GPa) but not in high pressures. In addition, according to Finite Element (FE) analysis it was found that 1 mm corner radius of steppers is the optimal value for the SIHPT process. پرونده مقاله -
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5 - An Axisymmetric Torsion Problem of an Elastic Layer on a Rigid Circular Base
B Kebli S Berkane F GuerracheA solution is presented to a doubly mixed boundary value problem of the torsion of an elastic layer, partially resting on a rigid circular base by a circular rigid punch attached to its surface. This problem is reduced to a system of dual integral equations using the Bo چکیده کاملA solution is presented to a doubly mixed boundary value problem of the torsion of an elastic layer, partially resting on a rigid circular base by a circular rigid punch attached to its surface. This problem is reduced to a system of dual integral equations using the Boussinesq stress functions and the Hankel integral transforms. With the help of the Gegenbauer expansion formula of the Bessel function we get an infinite algebraic system of simultaneous equations for calculating the unknown function of the problem. Both the two contact stresses under the punch and on the lower face of the layer are expressed as appropriate Chebyshev series. The effects of the radius of the disc with the rigid base and the layer thickness on the displacements, contact stresses as well as the shear stress and the stress singularity factor are discussed. A numerical application is also considered with some concluding results. پرونده مقاله -
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6 - Non-Linear Response of Torsional Buckling Piezoelectric Cylindrical Shell Reinforced with DWBNNTs Under Combination of Electro-Thermo-Mechanical Loadings in Elastic Foundation
M Sarvandi M.M Najafizadeh H SeyyedhasaniNanocomposites provide new properties and exploit unique synergism between materials. Polyvinylidene fluoride (PVDF) is an ideal piezoelectric matrix applicable in nanocomposites in a broad range of industries from oil and gas to electronics and automotive. And boron ni چکیده کاملNanocomposites provide new properties and exploit unique synergism between materials. Polyvinylidene fluoride (PVDF) is an ideal piezoelectric matrix applicable in nanocomposites in a broad range of industries from oil and gas to electronics and automotive. And boron nitride nanotubes (BNNTs) show high mechanical, electrical and chemical properties. In this paper, the critical torsional load of a composite tube made of PVDF reinforced with double-walled BNNTs is investigated, under a combination of electro-thermo-mechanical loading. First, a nanocomposite smart tube is modeled as an isotropic cylindrical shell in an elastic foundation. Next, employing the classical shell theory, strain-displacement equations are derived so loads and moments are obtained. Then, the total energy equation is determined, consisting of strain energy of shell, energy due to external work, and energy due to elastic foundation. Additionally, equilibrium equations are derived in cylindrical coordinates as triply orthogonal, utilizing Euler equations; subsequently, stability equations are developed through the equivalent method in adjacent points. The developed equations are solved using the wave technique to achieve critical torsional torque. Results indicated that critical torsional buckling load occurred in axial half-wave number m = 24 and circumferential wave number n = 1, for the investigated cylindrical shell. The results also showed that with the increase in the length-to-radius ratio and in the radius-to-shell thickness ratio, the critical torsional buckling load increased and decreased, respectively. Lastly, results are compared in various states through a numerical method. Moreover, stability equations are validated via comparison with the shell and sheet equations in the literature. پرونده مقاله -
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7 - Dispersion of Torsional Surface Wave in a Pre-Stressed Heterogeneous Layer Sandwiched Between Anisotropic Porous Half-Spaces Under Gravity
R.M Prasad S KunduThe study of surface waves in a layered media has their viable application in geophysical prospecting. This paper presents an analytical study on the dispersion of torsional surface wave in a pre-stressed heterogeneous layer sandwiched between a pre-stressed anisotropic چکیده کاملThe study of surface waves in a layered media has their viable application in geophysical prospecting. This paper presents an analytical study on the dispersion of torsional surface wave in a pre-stressed heterogeneous layer sandwiched between a pre-stressed anisotropic porous semi-infinite medium and gravitating anisotropic porous half-space. The non-homogeneity within the intermediate layer and upper semi-infinite medium is assumed to rise up, because of quadratic variation and exponential variation in directional rigidity, pre-stress, and density respectively. The displacement dispersion equation for the torsional wave velocity has been expressed in the term of Whitaker function and their derivatives. Dispersion relation and the closed-form solutions have been obtained analytically for the displacement in the layer and the half-spaces. It is determined that the existing geometry allows torsional surface waves to propagate and the observe exhibits that the layer width, layer inhomogeneity, frequency of heterogeneity in the heterogeneous medium has a great impact on the propagation of the torsional surface wave. The influence of inhomogeneities on torsional wave velocity is also mentioned graphically by means plotting the dimensionless phase velocity against non-dimensional wave number for distinct values of inhomogeneity parameters. پرونده مقاله -
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8 - Study of Torsional Vibrations of Composite Poroelastic Spherical Shell-Biot’s Extension Theory
R Gurijala M Reddy PeratiTorsional vibrations of composite poroelastic dissipative spherical shell are investigated in the framework of Biot’s extension theory.Here composite poroelastic spherical shell consists of two spherical shells, one is placed on other, and both are made of differe چکیده کاملTorsional vibrations of composite poroelastic dissipative spherical shell are investigated in the framework of Biot’s extension theory.Here composite poroelastic spherical shell consists of two spherical shells, one is placed on other, and both are made of different poroelastic materials. Consideration of the stress-free boundaries of outer surface and the perfect bonding between two shells leads to complex valued frequency equation. Limiting case when the ratio of thickness to inner radius is very small is investigated numerically. In this case, thick walled composite spherical shell reduces to thin composite spherical shell. For illustration purpose, four composite materials, namely, Berea sandstone saturated with water and kerosene, Shale rock saturated with water and kerosene are employed. The particular cases of a poroelastic solid spherical shell and poroelastic thick walled hollow spherical shell are discussed. If the shear viscosity of fluid is neglected, then the problem reduces to that of classical Biot’s theory. Phase velocity and attenuation are computed and the results are presented graphically. Comparison is made between the results of Biot’s extension theory and that of classical Biot’s theory. It is conclude that shear viscosity of fluid is causing the discrepancy of the numerical results. پرونده مقاله -
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9 - Free Torsional Vibration Analysis of Hollow and Solid Non-Uniform Rotating Shafts Using Distributed and Lumped Modeling Technique
A Saghafi M .A AziziIn this paper, the torsional free vibration of solid and hollow rotating shafts with non-uniform tapered elements are investigated. To this end, the exact solution and also transfer matrix for the free torsional vibration of a hollow tapered shaft element with uniform t چکیده کاملIn this paper, the torsional free vibration of solid and hollow rotating shafts with non-uniform tapered elements are investigated. To this end, the exact solution and also transfer matrix for the free torsional vibration of a hollow tapered shaft element with uniform thickness and also solid element are firstly obtained. Then, the natural frequencies are determined based on distributed and lumped modeling technique (DLMT). This technique is similar to transfer matrix method (TMM) but the exact solution is employed to obtain the transfer matrixes of the distributed element, therefore, there is no approximation and the natural frequencies and mode shapes are the exact values. To confirm the reliability of the presented method, the simulation results are compared with the results obtained from the other methods such as finite element method. It is shown that the proposed method provides highly accurate results and it can be simply applied to the complex torsional systems. پرونده مقاله -
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10 - Elasticity Exact Solution for an FGM Cylindrical Shaft with Piezoelectric Layers Under the Saint-Venant Torsion by Using Prandtl’s Formulation
M. R Eslami M Jabbari A Eskandarzadeh SabetFunctionally graded materials (FGMs) belong to a noble family of composite material possess material properties varying gradually in a desired direction or orientation. In a past decade, functionally graded materials were remained in an interest of material investigator چکیده کاملFunctionally graded materials (FGMs) belong to a noble family of composite material possess material properties varying gradually in a desired direction or orientation. In a past decade, functionally graded materials were remained in an interest of material investigators due to its prominent features, and have extensively used in almost every discipline of engineering which in turn significantly increases the number of research publication of FGM. In this paper the exact elasticity solution for an FGM circular shaft with piezo layers is analysed. piezoelectric layers are homogeneous and the modulus of elasticity for FGM varies continuously with the form of an exponential function. The shear modulus of the non-homogeneous FGM shaft is a given function of the Prandtl’s stress function of considered circular shaft when its material is homogeneous. state equations are derived. The Prandtl’s stress function and electric displacement potential function satisfy all conditions. The shearing stresses, torsional rigidity, torsional function for FGM layer and shearing stresses, electric displacements, torsional rigidity, electrical torsional rigidity ,torsional and electrical potential functions for piezoelectric layers are obtained. Exact analytical solution for hollow circular cross-section presented. At the end some graphs and conclusions are given. پرونده مقاله -
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11 - Torsion of Poroelastic Shaft with Hollow Elliptical Section
M Jabbari M.F KhansanamiIn this paper torsion of hollow Poroelastic shaft with Elliptical section is developed. Using the boundary equation scheme. It looks for a stress function where satisfied Poisson equation and vanishes on boundary. It also analyzed stress function and warping displacemen چکیده کاملIn this paper torsion of hollow Poroelastic shaft with Elliptical section is developed. Using the boundary equation scheme. It looks for a stress function where satisfied Poisson equation and vanishes on boundary. It also analyzed stress function and warping displacement for the hollow elliptical section in Poroelastic shaft. At the end, the result of elastic and poroelastic shaft in warping displacement and stress function is compared. پرونده مقاله -
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12 - Torsional Surface Wave Propagation in Anisotropic Layer Sandwiched Between Heterogeneous Half-Space
P.K Vaishnav S Kundu S.M Abo-Dahab A SahaThe present paper studies the possibility of propagation of torsional surface waves in an inhomogeneous anisotropic layer lying between two heterogeneous half-spaces (upper and lower half-space). Both the half-spaces are assumed to be under compressive initial stress. T چکیده کاملThe present paper studies the possibility of propagation of torsional surface waves in an inhomogeneous anisotropic layer lying between two heterogeneous half-spaces (upper and lower half-space). Both the half-spaces are assumed to be under compressive initial stress. The study reveals that under the assumed conditions, a torsional surface wave propagates in the medium. The dispersion relation of torsional surface wave has been obtained in the presence of heterogeneity, initial stress and anisotropic, and it is observed that the inhomogeneity factor due to quadratic and hyperbolic variations in rigidity, density and initial stress of the medium decreases the phase velocity as it increases. The result also shows that the initial stresses have a pronounced influence on the propagation of torsional surface waves. In the absence of anisotropy, Initial stress, inhomogeneity and rigidity of the upper half-space, then the dispersion relation coincide with the classical dispersion relation of Love wave. پرونده مقاله -
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13 - Torsional Stability of Cylindrical Shells with Functionally Graded Middle Layer on the Winkler Elastic Foundation
A.H Sofiyev S AdiguzelIn this study, the torsional stability analysis is presented for thin cylindrical with the functionally graded (FG) middle layer resting on the Winker elastic foundation. The mechanical properties of functionally graded material (FGM) are assumed to be graded in the thi چکیده کاملIn this study, the torsional stability analysis is presented for thin cylindrical with the functionally graded (FG) middle layer resting on the Winker elastic foundation. The mechanical properties of functionally graded material (FGM) are assumed to be graded in the thickness direction according to a simple power law and exponential distributions in terms of volume fractions of the constituents. The fundamental relations and basic equations of three-layered cylindrical shells with a FG middle layer resting on the Winker elastic foundation under torsional load are derived. Governing equations are solved by using the Galerkin method. The numerical results reveal that variations of the shell thickness-to-FG layer thickness ratio, radius-to-shell thickness ratio, lengths-to-radius ratio, foundation stiffness and compositional profiles have significant effects on the critical torsional load of three-layered cylindrical shells with a FG middle layer. The results are verified by comparing the obtained values with those in the existing literature. پرونده مقاله -
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14 - Thermal Creep Analysis of Functionally Graded Thick-Walled Cylinder Subjected to Torsion and Internal and External Pressure
S Sharma S Yadav R SharmaSafety analysis has been done for the torsion of a functionally graded thick-walled circular cylinder under internal and external pressure subjected to thermal loading. In order to determine stresses the concept of Seth’s transition theory based on generalized pri چکیده کاملSafety analysis has been done for the torsion of a functionally graded thick-walled circular cylinder under internal and external pressure subjected to thermal loading. In order to determine stresses the concept of Seth’s transition theory based on generalized principal strain measure has been used. This theory simplifies the set of mechanical equations by mentioning the order of the measure of deformation. This theory helps to achieve better agreement between the theoretical and experimental results. Results have been analyzed with or without thermal effects for functionally graded and homogeneous cylinder with linear and nonlinear strain measure.From the analysis, it has been concluded that in creep torsion cylinder made up of less functionally graded material (FGM) under pressure is better choice for designing point of view as compared to homogeneous cylinder. This is due to shear stresses which are maximum for cylinder made up of functionally graded material as compared to homogeneous material. پرونده مقاله -
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15 - Torsional Waves in Prestressed Fiber Reinforced Medium Subjected to Magnetic Field
R Kakar S KakarThe propagation of torsional waves in a prestressed fiber-reinforced half-space under the effect of magnetic field and gravity has been discussed. The problem has been solved analytically using Whittaker function to obtain the exact solution frequency equations. Numeric چکیده کاملThe propagation of torsional waves in a prestressed fiber-reinforced half-space under the effect of magnetic field and gravity has been discussed. The problem has been solved analytically using Whittaker function to obtain the exact solution frequency equations. Numerical results for stress, gravity and magnetic field are given and illustrated graphically. Comparisons are made with the results predicted by the boundary value condition for rigid boundary and for traction free boundary in the presence and in the absence of the effect of a magnetic field, gravity and stress. It is found that the reinforcement, gravity and magnetic field have great effects on the distribution. پرونده مقاله -
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16 - Longitudinal-Torsional and Two Plane Transverse Vibrations of a Composite Timoshenko Rotor
M Irani Rahagi A Mohebbi H AfshariIn this paper, two kinds of vibrations are considered for a composite Timoshenko rotor: longitudinal-torsional vibration and two plane transverse one. The kinetic and potential energies and virtual work due to the gyroscopic effects are calculated and the set of six gov چکیده کاملIn this paper, two kinds of vibrations are considered for a composite Timoshenko rotor: longitudinal-torsional vibration and two plane transverse one. The kinetic and potential energies and virtual work due to the gyroscopic effects are calculated and the set of six governing equations and boundary conditions are derived using Hamilton principle. Differential quadrature method (DQM) is used as a strong numerical method and natural frequencies and mode shapes are derived. Effects of the rotating speed and the lamination angle on the natural frequencies are studied for various boundary conditions; meanwhile, critical speeds of the rotor are determined. Two kinds of critical speeds are considered for the rotor: the resonance speed, which happens as rotor rotates near one of the natural frequencies, and the instability speed, which occurs as value of the first natural frequency decreases to zero and rotor becomes instable. پرونده مقاله -
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17 - Homological dimensions of complexes of R-modules
N. Tayarzadeh Esmaiel Hosseini Sh. NiknejadLet R be an associative ring with identity, C(R) be the category of com-plexes of R-modules and Flat(C(R)) be the class of all at complexes of R-modules. We show that the at cotorsion theory (Flat(C(R)); Flat(C(R))−)have enough injectives in C(R). As an applicatio چکیده کاملLet R be an associative ring with identity, C(R) be the category of com-plexes of R-modules and Flat(C(R)) be the class of all at complexes of R-modules. We show that the at cotorsion theory (Flat(C(R)); Flat(C(R))−)have enough injectives in C(R). As an application, we prove that for each atcomplex F and each complex Y of R-modules, Exti(F,X)= 0, whenever Ris n-perfect and i > n. پرونده مقاله -
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18 - بهبود عملکرد مبدل حرارتی پیچشی کنگره‌دار دوسیاله حاوی نانوسیالات هیبریدی
مجتبی جمعیتی حسین پورمحمدیاندر این پژوهش به صورت عددی و با استفاده از دینامیک سیالات محاسباتی به بررسی اثر کنگره درون مبدل حرارتی پیچشی دوسیاله حاوی نانوسیال هیبریدی آب-مس-نانولوله کربنی پرداخته می‌شود. هندسه مبدل حرارتی پیچیشی با استفاده از نرم افزار دیزاین مدلر آماده می‌گردد. همچنین به منظور تحل چکیده کاملدر این پژوهش به صورت عددی و با استفاده از دینامیک سیالات محاسباتی به بررسی اثر کنگره درون مبدل حرارتی پیچشی دوسیاله حاوی نانوسیال هیبریدی آب-مس-نانولوله کربنی پرداخته می‌شود. هندسه مبدل حرارتی پیچیشی با استفاده از نرم افزار دیزاین مدلر آماده می‌گردد. همچنین به منظور تحلیل سیالاتی از روش حجم محدود و نرم افزار انسیس فلوئنت استفاده می‌شود. جریان نانوسیال هیبریدی در توربولنت بوده و به منظور مدل سازی آن از مدل توربولانسی کا امگا استفاده می‌شود. هندسه مبدل حرارتی پیچشی ساده با مبدل حرارتی پیچشی به همراه کنگره مورد مقایسه قرار گرفته و نتایج خروجی به صورت نمودار‌های عدد ناسلت متوسط، افت فشار و شاخص PEC ارائه می‌گردد. مطالعه برای اعداد رینولدز 6000 تا 24000، کسرحجمی 1 تا 5 درصد و سه ارتفاع مختلف 1، 2 و 3 میلی‌متر از کنگره انجام می‌شود. نتایج بدست آمده از شبیه سازی عددی نشان میدهد که استفاده از نانوسیال هیبریدی آب-مس-نانو لوله کربنی نسبت به سیال پایه آب باعث عملکرد حرارتی بیشتری می‌شود. پرونده مقاله -
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19 - Evaluation of Torsional Single Story Structure During Earthquake According to Canadian provision
Seiyed Ali Haj Seiyed Taghia Masoud Ebrahimi Abdoulreza Sarvghad MoghadamcIn this article, we tried to emphasis in how the range of torsionally stiff and flexible single story buildings works. The designed base was according to provisions of the Canadian standard, 2005 NBCC. The behavior of nonlinear dynamic time history of eight building mod چکیده کاملIn this article, we tried to emphasis in how the range of torsionally stiff and flexible single story buildings works. The designed base was according to provisions of the Canadian standard, 2005 NBCC. The behavior of nonlinear dynamic time history of eight building models subjected to seven horizontal bi-directional ground motions compatible with design spectra are investigated. These models cover a wide range of torsionally stiff to flexible buildings. Response parameters are element ductility demand and building story drift ratio. These criteria are appropriate indices for structural and nonstructural damages, respectively. This investigation shows that the linear static and dynamic analysis of building codes such as the 2005 NBCC and its framework are not generally adequate for structures with extremely low torsional stiffness. The provisions in mentioned codes and its framework are able to limit ductility demand, but they do not limit drift to the allowable level for extremely torsional structure. پرونده مقاله -
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20 - Seismic Performance of Torsionally Stiff and Flexible Single Story Buildings Designed Based on Iranian Seismic Code(Standard 2800)
Seiyed Ali Haj Seiyed Taghia A.S. MoghadamThis paper examines differences in performances of a range of torsionally stiff and flexible single story buildings designed with the provisions of Iranian Standard 2800. Seismic nonlinear dynamic time history behavior of eight building models subjected to seven horizon چکیده کاملThis paper examines differences in performances of a range of torsionally stiff and flexible single story buildings designed with the provisions of Iranian Standard 2800. Seismic nonlinear dynamic time history behavior of eight building models subjected to seven horizontal bi-directional design spectra compatible ground motions are investigated. These models cover a wide range of very torsionally stiff to very flexible buildings. Response parameters are element ductility demand and building story drift ratio. These criteria are appropriate indices for structural and nonstructural damages, respectively. This investigation shows that the linear static analysis of building code such as Iranian Standard 2800 is not generally adequate for structures with very low torsional stiffness. پرونده مقاله -
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21 - 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 چکیده کاملWhen 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. پرونده مقاله -
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22 - 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 چکیده کاملHigh-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. پرونده مقاله -
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23 - Design and Fabrication of a Longitudinal-Torsional Ultrasonic Transducer
Yahya Radi Najafabadi Reza Nosouhi Frahad SajajidA hybrid longitudinal-torsional ultrasonic transducer is designed and fabricated in this research. Thedesign of the transducer was performed using the FE method with ABAQUS software, with the aimof combining the longitudinal and torsional vibration modes. The transducer چکیده کاملA hybrid longitudinal-torsional ultrasonic transducer is designed and fabricated in this research. Thedesign of the transducer was performed using the FE method with ABAQUS software, with the aimof combining the longitudinal and torsional vibration modes. The transducer horn is then fabricatedusing a 4-axis milling machine. The PZT stacks are employed in order to excite the transducer. Thetransducer body is fabricated with grade 5 titanium for its appropriate mechanical properties. Thetransducer is then assembled and the experimental tests are carried out to measure the vibrationamplitude in both longitudinal and torsional directions using an Eddy current displacement sensor.Theresults showed that the resonance frequencies of both the torsional and longitudinal modes arethe same and experimental results are in good agreement with the FE results. The transducer can beused as a vibration tool for vibration assisted drilling which can produce both longitudinal andtorsional vibrations. پرونده مقاله -
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24 - میراسازی گشتاورهای پیچشی روی محور توربین- ژنراتور به کمک پایدارسازهای نوین ژنتیکی و فازی
عباس شولایی محمد بیاتی پوده غضنفر شاهقلیانحضور تنش‌های روی محور توربین- ژنراتور که محصول بروز اغتشاش در سیستم‌های قدرت هستند، باعث کاهش عمر مفید محور می‌شود. در این مقاله میراسازی سریع و کنترل این تنش‌ها، با کمک پایدارسازهای نوین محقق می‌گردد. پایدارساز ترکیبی در این مقاله بر روی سیستم تحریک ولتاژ ژنراتور و سیس چکیده کاملحضور تنش‌های روی محور توربین- ژنراتور که محصول بروز اغتشاش در سیستم‌های قدرت هستند، باعث کاهش عمر مفید محور می‌شود. در این مقاله میراسازی سریع و کنترل این تنش‌ها، با کمک پایدارسازهای نوین محقق می‌گردد. پایدارساز ترکیبی در این مقاله بر روی سیستم تحریک ولتاژ ژنراتور و سیستم کنترلی خط انتقال جریان مستقیم عمل می‌کند؛ در تنظیم پارامترهای این پایدارساز از الگوریتم ژنتیک با هدف کاهش تنش‌ها، یاری گرفته می‌شود که تاثیر این پایدارساز را چندین برابر می‌نماید. همچنین در کنترل بهتر این پایدارساز از روش کنترل منطق فازی استفاده می‌شود که تاثیر قابل توجهی در کنترل تنش‌های به وجود آمده در سیستم مورد مطالعه دارد. نتایج شبیه‌سازی موید تاثیر پایدارسازهای طراحی شده در کنترل گشتاورهای پیچشی روی محور توربین- ژنراتور است. پرونده مقاله -
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25 - بررسی تحلیلی و آیین‌نامه‌ای نامنظمی‌های پیچشی در سازه‌های کوتاه تا میان مرتبه
بیژن صناعتی جمال احمدیزلزلههای اخیر نشان داده‌اند که وجود نامنظمی پیچشی در سازه‌ها، عاملی است که باعث آسیب شدید سازه‌ای می‌شود. در ویرایش‌های قبلی استاندارد 2800، بحثی از نامنظمی پیچشی نشده بود. در ویرایش چهارم، ضوابط این نوع نامنظمی هم گنجانده شده است. هدف از تحقیق حاضر، بررسی این ضوابط با چکیده کاملزلزلههای اخیر نشان داده‌اند که وجود نامنظمی پیچشی در سازه‌ها، عاملی است که باعث آسیب شدید سازه‌ای می‌شود. در ویرایش‌های قبلی استاندارد 2800، بحثی از نامنظمی پیچشی نشده بود. در ویرایش چهارم، ضوابط این نوع نامنظمی هم گنجانده شده است. هدف از تحقیق حاضر، بررسی این ضوابط با استفاده از نتایج روش تحلیلی خطی طیفی درنرم افزارETABS 2015 ، سازه به حالت شبه دینامیکی تحلیل و پیچش تصادفی در نظر گرفته شده ، مقایسة نتایج به‌دست‌آمده با ضوابط سایر آیین‌نامه‌ها است. پارامترهای بررسی شده عبارت‌اند از: موقعیت دیوارهای برشی، تعداد طبقات و تعداد محورها. به‌منظور بررسی نامنظمی پیچشی در جهت Y پلان، موقعیت دیوارهای برشی حول محور X و Y به ترتیب متقارن و نامتقارن در نظر گرفته شده‌اند. با آنالیز 96 مدل تحلیلی مشخص گردید که حداکثر مقدار ضریب نامنظمی پیچشی با کاهش تعداد طبقات سازه افزایش می‌یابد. طبقات بالاتر دارای ضریب نامنظمی پیچشی کمتری نسبت به طبقات پایین‌تر هستند. نتایج به‌دست‌آمده برای دوران کف طبقات، برعکس نتیجة مربوط به ضریب نامنظمی پیچشی است. یک رابطه نیز برای ارتباط دادن مستقیم ضریب نامنظمی پیچشی و زاویة چرخش طبقات ارائه شده است. پرونده مقاله -
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26 - بررسی ضریب نامعینی در ساختمانهای بتنی با سیستم سازه‌ای غیر موازی
عظیم بنی جلالی سید سینا کورهلیدرمقاله حاضر به بررسی ضریب نامعینی درساختمانهای بتنی با سیستم سازه ای غیرموازی پرداخته شده است. چهار سازه بتنی سه بعدی 5و 7 طبقه با سه و چهار دهانه با سیستم قاب خمشی درنرم افزار ایتبس مورد تحلیل و طراحی قرارگرفته است. جهت برآورد ضریب نامعینی با تحلیل خطی، مقاومت جانبی و چکیده کاملدرمقاله حاضر به بررسی ضریب نامعینی درساختمانهای بتنی با سیستم سازه ای غیرموازی پرداخته شده است. چهار سازه بتنی سه بعدی 5و 7 طبقه با سه و چهار دهانه با سیستم قاب خمشی درنرم افزار ایتبس مورد تحلیل و طراحی قرارگرفته است. جهت برآورد ضریب نامعینی با تحلیل خطی، مقاومت جانبی و نامنظمی پیچشی سازه های مورد نظر با استفاده از نرم افزار مورد بررسی قرار گرفته است. در ساختمانهای مورد مطالعه که دارای سیستم نامنظم در پلان می باشند ابتدا طبقاتی که میزان برش در آنها از 35 درصد برش پایه تجاوز می کند را مشخص نموده و سپس مقاومت خمشی تیر حذف شده و کاهش مقاومت جانبی طبقه همچنین ایجاد نامنظمی شدید پیچشی کنترل می گردد. نتایج بدست آمده نشان میدهد درسازه های مورد مطالعه نامنظمی شدید پیچشی وجود نداشته و درصدکاهش مقاومت درتمامی سازه ها کمتراز 33 درصد می باشد و ضریب نامعینی میبایست برابر یک درنظر گرفته می شود. پرونده مقاله -
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27 - تأثیر میراگر پیچشی-تسلیمی بر جذب انرژی ارتعاشی سازه
علیرضا انصاری سعید عباسی اصغر رسولیبرای بهبود رفتار سیستم لرزه بر و افزایش ظرفیت سازه ، اﺳﺘﻔﺎده از میراگرها روشی مناسب برای استهلاک انرژی و کاهش تقاضای لرزه ای می باشد. رفتار سازه ها در هنگام زمین لرزه رابطه مستقیم با سختی، شکل پذیری و منحنی های هیسترزیس استهلاک انرژی سیستم مقاوم دارد و کنترل و استهلاک چکیده کاملبرای بهبود رفتار سیستم لرزه بر و افزایش ظرفیت سازه ، اﺳﺘﻔﺎده از میراگرها روشی مناسب برای استهلاک انرژی و کاهش تقاضای لرزه ای می باشد. رفتار سازه ها در هنگام زمین لرزه رابطه مستقیم با سختی، شکل پذیری و منحنی های هیسترزیس استهلاک انرژی سیستم مقاوم دارد و کنترل و استهلاک انرژی ورودی به سازه به منظور کاهش خسارت ناشی از زمین لرزه، روش مناسب برای پاسخ به نیاز سازه ها می باشد. بدین منظــور سیسـتمی معرفـی شـده است که با کاربرد آن حین وقوع زلزله و به دلیل شکل پذیری بالایی که دارد مانند یک فیوز عمل نموده و از وقــوع خرابـی در المان های اصلی سازه جلوگیری می کند. در این مطالعه نوع خاصی از میراگر تسلیمی با رفتار پیچشی کـه آن را میراگر تسلیمی-پیچشی یـا بـه اختصـار TFD[1] می نامیم مورد بررسی قرار می گیرد و توان جذب انرژی سازه مورد بررسی قرار می گیرد. بدین منظور سیستم پیشنهادی به صورت عددی در نرم افزار ABAQUS مورد بررسی غیر خطی قرار گرفته است و نتایج این تحقیق بدست آمده حاکی از آن است که استفاده از میراگر TFD سبب استهلاک انرژی در عضو رابط شده و سهم سایر اعضای سازه را در جذب انرژی به طور چشم گیری کاهش داده و رفتار سازه را در سطح عملکرد بهتری قرار می دهد.[1] Torsion Frame Damper پرونده مقاله -
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28 - Comparative Study of Seismic Response of Base Isolated Building with Plan Eccentricities and Elevation Eccentricities
Lavkesh Rameshrao WankhadeBase isolation is one of the most widely accepted techniques to protect structures and to mitigate the risk to life and property from strong earthquakes. In this paper, the effect of mass asymmetry in symmetric building with unidirectional and bidirectional eccentriciti چکیده کاملBase isolation is one of the most widely accepted techniques to protect structures and to mitigate the risk to life and property from strong earthquakes. In this paper, the effect of mass asymmetry in symmetric building with unidirectional and bidirectional eccentricities and asymmetric building with upward and downward eccentricities in elevation is studied. To study the effect of torsion in seismic behavior of base isolated structures, a symmetric and asymmetric thirteen story concrete building is chosen as reference model. These models with mass eccentricity of 5%, 10%, 15% and 20% of greatest dimension of building in unidirection and bidirection are considered. The response spectrum and linear time history analysis of this eccentric model of fixed base and base isolated building using ETABS software is done. The symmetric and asymmetric fixed base and base isolated building having eccentricity in plan and elevation are compared for parameters such as maximum shear force, torsion, bending moment, lateral displacement, storey drift, storey acceleration and base shear. It is concluded that base isolation is very effective for various mass eccentric models. Response of base isolated mass eccentric model even in large mass eccentricity reduces as compared to fixed base building. پرونده مقاله -
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29 - Practical Engineering Approach for Generating the Torsional Earthquake Excitation from Translational Components
Sandeep C. Potnis Raviji S. Desai I.D GuptaWorldwide networks of seismic recording instruments mostly record only translational ground motion in two or three orthogonal directions. Rotational component of earthquake is not commonly recorded. Several theories are available to estimate a torsional component from r چکیده کاملWorldwide networks of seismic recording instruments mostly record only translational ground motion in two or three orthogonal directions. Rotational component of earthquake is not commonly recorded. Several theories are available to estimate a torsional component from recorded translational components of ground motion. In this paper detailed investigations are made to study the relative performance of some available methods. This paper suggests a practical approach for obtaining true SH (S-wave having particle motion in horizontal direction) component from two recorded horizontal components of ground excitation. This new approach will help to obtain optimum torsional time histories from translational time histories. پرونده مقاله -
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30 - Torsion of cylindrically poroelasic circular shaft with radial inhomogeneity .some exact solutions for extruder
mohammad farid khansanami Faranak KhansanamiTorsion of elastic and poroelastic circular shaft of radially inhomogeneous, cylindrically orthotropic materials is studied with emphasis on the end effects example for extruder. To examine the conjecture of Saint-Venant’s torsion, we consider torsion of circular s چکیده کاملTorsion of elastic and poroelastic circular shaft of radially inhomogeneous, cylindrically orthotropic materials is studied with emphasis on the end effects example for extruder. To examine the conjecture of Saint-Venant’s torsion, we consider torsion of circular shaft with one end fixed and the other end free on which tractions that results in a pure torque are prescribed arbitrarily over the free end surface. Exact solutions that satisfy the prescribed boundary conditions point by point over the entire boundary surfaces are derived in a unified manner for cylindrically orthotropic shafts with or without radial inhomogeneity and for their coun- terparts of Saint-Venant’s torsion. Stress diffusion due to the end effect is examined in the light of the exact solutions.The present study enables us to assess Saint-Venant’s principle as applied to anisotropic, non-homogeneous poroelastic bodies in general and to evaluate the stress diffusion in torsion of radially inhomogeneous, cylindrically orthotropic cylinders in particular. The following conclusions can be drawn from the analysis. پرونده مقاله -
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31 - Torsion of cylindrically poroelasic circular shaft with radial inhomogeneity .some exact solutions for extruder
محمد فرید خان سمنی فرانک خان سمنیTorsion of elastic and poroelastic circular shaft of radially inhomogeneous, cylindrically orthotropic materials is studied with emphasis on the end effects example for extruder. To examine the conjecture of Saint-Venant’s torsion, we consider torsion of circular s چکیده کاملTorsion of elastic and poroelastic circular shaft of radially inhomogeneous, cylindrically orthotropic materials is studied with emphasis on the end effects example for extruder. To examine the conjecture of Saint-Venant’s torsion, we consider torsion of circular shaft with one end fixed and the other end free on which tractions that results in a pure torque are prescribed arbitrarily over the free end surface. Exact solutions that satisfy the prescribed boundary conditions point by point over the entire boundary surfaces are derived in a unified manner for cylindrically orthotropic shafts with or without radial inhomogeneity and for their coun- terparts of Saint-Venant’s torsion. Stress diffusion due to the end effect is examined in the light of the exact solutions.The present study enables us to assess Saint-Venant’s principle as applied to anisotropic, non-homogeneous poroelastic bodies in general and to evaluate the stress diffusion in torsion of radially inhomogeneous, cylindrically orthotropic cylinders in particular. The following conclusions can be drawn from the analysis پرونده مقاله -
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32 - Effect of HPT and CGP Processes on the Copper Me-chanical Properties
ش. جعفرزاده H. Bisad ه. میانجی ع. زینعلیOne of the most common methods for production of ultra fine grained materials is severe plastic deformation (SPD). In this study, constrained groove pressing (CGP) and high pressure torsion (HPT) processes as effective methods of severe plastic deformation for the strai چکیده کاملOne of the most common methods for production of ultra fine grained materials is severe plastic deformation (SPD). In this study, constrained groove pressing (CGP) and high pressure torsion (HPT) processes as effective methods of severe plastic deformation for the strain imposed on the pure copper were used. This paper presents the results of an experimental research, to review the influence of CGP and HPT processes of the mechanical properties such as hardness and tensile on copper samples has been done. The results of tensile and hardness tests represented that due to applying CGP process, strength and hardness of samples were increased significantly.The results of HPT process showed that hardness in the radial direction is variable and away from disk center in the radial direction continuously increases. Of course, in higher pressing steps the slight decrease in strength and hardness is observed, more explanation is given in this paper. Finally, comparison results of the two methods, their advantages and limitations of them are studied. پرونده مقاله -
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33 - Torsional Buckling Analysis of a Vehicle Composite Drive Shaft Based on a High Order Theory with Considering Initial Imperfection
مهدی حسینی محمد شرعیاتIn this paper, the finite element analysis of stability problem of vehicle composite drive shafts subjected to torsional loading is studied. First, using the minimum total potential energy principle, the governing equations are derived and then they are solved by finite چکیده کاملIn this paper, the finite element analysis of stability problem of vehicle composite drive shafts subjected to torsional loading is studied. First, using the minimum total potential energy principle, the governing equations are derived and then they are solved by finite element method. The initial geometrical imperfection which is usually in the form of radial displacement, is taken into consideration in the formulation and the displacement field is expressed according to the third order shear deformation theory. Finally, Budyanski’s criterion is employed for determination of the critical buckling load and the effect of different parameters on the buckling behavior is studied. The results show that the stacking sequence, has a significant effect on the buckling torque. Furthermore, the buckling torque increases as the initial imperfection amplitude decreases. پرونده مقاله -
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34 - Characterization of $\delta$-double derivations on rings and algebras
A. HosseiniThe main purpose of this article is to offer some characterizations of $\delta$-doublederivations on rings and algebras. To reach this goal, we prove the following theorem:Let $n > 1$ be an integer and let $\mathcal{R}$ be an $n!$-torsion free ring with the identity چکیده کاملThe main purpose of this article is to offer some characterizations of $\delta$-doublederivations on rings and algebras. To reach this goal, we prove the following theorem:Let $n > 1$ be an integer and let $\mathcal{R}$ be an $n!$-torsion free ring with the identity element $1$.Suppose that there exist two additive mappings $d,\delta:R\to R$ such that$$d(x^n) =\Sigma^n_{j=1}x^{n-j}d(x)x^{j-1}+\Sigma^{n-2}_{k=0} \Sigma^{n-2-k}_{i=0}x^k\delta(x)x^i\delta(x)x^{n-2-k-i}$$is fulfilled for all $x\in \mathcal{R}$. If $\delta(1) = 0$, then $d$ is a Jordan $\delta$-double derivation. In particular,if $\mathcal{R}$ is a semiprime algebra and further, $\delta^2(x^2) = \delta^2(x)x + x\delta^2(x) + 2(\delta(x))^2$ holds for all $x\in \mathcal{R}$, then $d-\frac{1}{2}\delta^2$ is an ordinary derivation on $\mathcal{R}$. پرونده مقاله -
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35 - Characterization of $(\delta, \varepsilon)$-double derivation on rings and algebras
Z. Jokar A. NiknamThis paper is an attempt to prove the following result:Let $n>1$ be an integer and let $\mathcal{R}$ be a $n!$-torsion-free ring with the identity element. Suppose that $d, \delta, \varepsilon$ are additive mappings satisfying\begin{equation}d(x^n) = \sum^{n}_{j=1}x^ چکیده کاملThis paper is an attempt to prove the following result:Let $n>1$ be an integer and let $\mathcal{R}$ be a $n!$-torsion-free ring with the identity element. Suppose that $d, \delta, \varepsilon$ are additive mappings satisfying\begin{equation}d(x^n) = \sum^{n}_{j=1}x^{n-j}d(x)x^{j-1}+\sum^{n-1}_{j=1}\sum^{j}_{i=1}x^{n-1-j}\Big(\delta(x)x^{j-i}\varepsilon(x)+\varepsilon(x)x^{j-i}\delta(x)\Big)x^{i-1}\quad\end{equation}for all $x \in \mathcal{R}$. If $\delta(e) = \varepsilon(e) = 0$, then $d$ is a Jordan $(\delta, \varepsilon)$-double derivation.In particular, if $\mathcal{R}$ is a semiprime algebra and further, $\delta(x) \varepsilon(x) + \varepsilon(x) \delta(x) = \frac{1}{2}\Big[(\delta \varepsilon + \varepsilon \delta)(x^2) - (\delta \varepsilon(x) + \varepsilon \delta(x))x - x (\delta \varepsilon(x) + \varepsilon \delta(x))\Big]$ holds for all $x \in \mathcal{R}$, then $d - \frac{\delta \varepsilon + \varepsilon \delta}{2}$ is a derivation on $\mathcal{R}$. پرونده مقاله -
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36 - بررسی وقوع استحاله فازی در آلیاژ Ti-6242 و تعیین دمای استحاله آن
علیرضا حجاری مریم مرکباتی رامین حسینی یاور منصوری مهدی عباسیهدف از پژوهش حاضر تعیین دمای استحاله‌ی دو آلیاژ Ti-6242 و بررسی تأثیر مقادیر مختلف عناصر بر پایداری فازهای آلفا و بتا با استفاده از بررسی‌های ریزساختاری و آزمایش پیچش گرم است. تعیین دمای استحاله‌ی بتا نقش مهمی در طراحی دقیق عملیات ترمومکانیکی و عملیات حرارتی در آلیاژهای چکیده کاملهدف از پژوهش حاضر تعیین دمای استحاله‌ی دو آلیاژ Ti-6242 و بررسی تأثیر مقادیر مختلف عناصر بر پایداری فازهای آلفا و بتا با استفاده از بررسی‌های ریزساختاری و آزمایش پیچش گرم است. تعیین دمای استحاله‌ی بتا نقش مهمی در طراحی دقیق عملیات ترمومکانیکی و عملیات حرارتی در آلیاژهای تیتانیم دارد و از اینرو عامل تأثیرگذاری بر خواص مکانیکی آلیاژهای دوفازی تیتانیم می‌باشد. برای این منظور، آزمایش پیچش گرم با نرخ کرنش s-1 001/0 در بازه‌ی دمایی ˚C960 تا ˚C1090 و نرخ سرمایش ˚C/s5/0 انجام شد. همچنین بررسی‌های متالوگرافی با هدف تعیین دمای جوانه‌زنی فاز آلفای مرزدانه‌ای و مشاهده‌ی تحولات ریزساختاری حین استحاله‌ی فازی روی نمونه‌های عملیات حرارتی شده در بازه‌ی دمایی °C980 تا °C1020 به مدت 40 دقیقه و کوئنچ در آب، صورت گرفت. بررسی‌ها نشان داد که با افزایش 10 درصدی Aleq/Moeq ، دمای استحاله‌ی بتا در آلیاژ Ti-6242 به میزان حدود °C5 افزایش می‌یابد. به این ترتیب، دمای استحاله‌ی این دو آلیاژ بین °C1000 تا °C1010 تخمین زده شد. همچنین دمای استحاله حاصل از آزمایش پیچش گرم دارای انحرافی حدود °C10 با نتایج حاصل از متالوگرافی است که این اختلاف ناشی از وقوع استحاله تسریع شده به دلیل اعمال کرنش است. پرونده مقاله -
دسترسی آزاد مقاله
37 - بررسی فرآیندهای ترمیم دینامیکی و استاتیکی در تغییرشکل گرم آلیاژ تیتانیوم SP-700
امیرحسین شیخعلی مریم مرکباتی سید مهدی عباسیبه منظور بررسی فرآیندهای ترمیم دینامیکی و استاتیکی آلیاژ SP-700، در این تحقیق آزمایش پیچش گرم پیوسته و منقطع در دماهای 850 و ºC1000 با کرنش‌ها و زمان‌های بین پاسی مختلف انجام شد. مکانیزم غالب تغییرشکل در دمای ºC1000، تبلورمجدد دینامیکی (DRX) است. درحالیکه در د چکیده کاملبه منظور بررسی فرآیندهای ترمیم دینامیکی و استاتیکی آلیاژ SP-700، در این تحقیق آزمایش پیچش گرم پیوسته و منقطع در دماهای 850 و ºC1000 با کرنش‌ها و زمان‌های بین پاسی مختلف انجام شد. مکانیزم غالب تغییرشکل در دمای ºC1000، تبلورمجدد دینامیکی (DRX) است. درحالیکه در دمای ºC850، تضرس و درهم تنیدگی مرزدانه‌ها مشاهده شد. با این وجود ریزساختار نمونه پیچش گرم در دمای ºC850 حاوی دانه‌های ریز (10-3 میکرون) بوده که بیانگر وقوع تبلورمجدد دینامیکی است. دانه‌های تبلورمجدد یافته در اطراف مرزدانه‌ها و نقاط سه‌گانه از طریق مکانیزم تحدب تشکیل شده‌اند. با افزایش کرنش پاس اول (5/0ε=) در دمای ºC1000، بدلیل افزایش نیرو محرکه جوانه‌زنی و رشد دانه‌های جدید، سینتیک فرآیند ترمیم استاتیکی نیز افزایش می‌یابد. اما در کرنش‌های حالت پایدار (1ε=) بدلیل وقوع تبلورمجدد دینامیکی کامل حین تغییرشکل، نیرو محرکه و در نتیجه سینتیک فرآیند ترمیم استاتیکی کمتر است. در واقع، در دمای ºC850 علاوه بر ترمیم استاتیکی، وقوع استحاله فازی α به β نیز در کسر نرم‌شدگی تاثیر دارد. پرونده مقاله -
دسترسی آزاد مقاله
38 - Fracture analysis of multiple axisymmetric interfacial cracks in an FGM Coated orthotropic layer
Behrooz MomeniBased on the distributed dislocation technique, an analytical solution for the orthotropic layer with functionally graded material (FGM) orthotropic coating containing multiple axisymmetric interfacial cracks subjected to torsional loading is investigated. It is assumed چکیده کاملBased on the distributed dislocation technique, an analytical solution for the orthotropic layer with functionally graded material (FGM) orthotropic coating containing multiple axisymmetric interfacial cracks subjected to torsional loading is investigated. It is assumed that the material properties of the FGM orthotropic coating vary power-law form along the thickness of the layer. At first, by using the Hankel transform, the solution for Somigliana type rotational ring dislocation in the layer and its coating is obtained. Then, the dislocation solution is used to derive a set of singular integral equations for a system of coaxial axisymmetric interface cracks, including penny-shaped and annular cracks. cracks with Cauchy type kernel. The integral equations are of Cauchy singular type, which are solved by Erdogan’s collocation method for dislocation density on the surface of interfacial crack and the results are used to determine stress intensity factors (SIFs) for axisymmetric interface cracks. Finally, several examples are provided to study the effects of the non-homogeneity constant, orthotropy parameter and thickness of FGM coating on the SIFs for interfacial cracks.. The effects of the non-homogeneity constant, orthotropy parameter and thickness of FGM coating as well as the interaction of multiple interfacial cracks on the SIFs are investigated. The results reveal that the value of the SIFs decreases with increasing the non-homogeneity parameter, orthotropy and thickness of FGM coating. The SIFs for inner tips of annular interface crack are larger than the outer tips. پرونده مقاله -
دسترسی آزاد مقاله
39 - Analysis of Stress Intensity Factors in Hollow Cylinders Reinforced by an Effective Coating Containing Multiple Cracks
Mostafa Karimi Alireza HassaniIn this paper, the solution of an isotropic hollow cylinder, with an isotropic coating, weakened by multiple radial cracks is studied. The hollow cylinder and its coating are under Saint-Venant torsional loading. The series solution is then derived for displacement and چکیده کاملIn this paper, the solution of an isotropic hollow cylinder, with an isotropic coating, weakened by multiple radial cracks is studied. The hollow cylinder and its coating are under Saint-Venant torsional loading. The series solution is then derived for displacement and stress fields in the cross section of the cylinder containing a Volterra-type screw dislocation. The dislocation solution is employed to derive a set of Cauchy singular integral equations for the analysis of multiple curved cracks. The solution to these equations is used to determine the torsional rigidity of the domain and the stress intensity factors (SIFs) for the tips of the cracks. Finally, several examples are presented to show the effect of the coating on the reduction of the mechanical stress intensity factor in the hollow cylinder.According to the above review, the fracture problem of the shafts under torsion is an interesting problem. It is worth noting that all of the above mentioned works were limited to the shafts with particular orientation and geometry پرونده مقاله -
دسترسی آزاد مقاله
40 - بررسی تحلیلی رفتار کمانشی ستون دارای ترک بر مبنای خاصیت فیزیکی تابع دلتای دیراک
سید هادی دهقان منشادی رهام ریحانی Mohammad Ali Dashti Rahmat Abadiتابع دلتای دیراک نمایش ساده و مؤثر بارهای نقطه‌ای و تکینگی‌ها را در انواع مسائل سازه‌ای امکان‌پذیر می‌کند که اغلب به راه حل‌های بسته منجر می‌شود. در این پژوهش کمانش ستونی دوسر ساده با یک و دو ترک به صورت تحلیلی مورد بررسی قرار گرفته است. با وجود این‌که در سال‌های اخیر چکیده کاملتابع دلتای دیراک نمایش ساده و مؤثر بارهای نقطه‌ای و تکینگی‌ها را در انواع مسائل سازه‌ای امکان‌پذیر می‌کند که اغلب به راه حل‌های بسته منجر می‌شود. در این پژوهش کمانش ستونی دوسر ساده با یک و دو ترک به صورت تحلیلی مورد بررسی قرار گرفته است. با وجود این‌که در سال‌های اخیر این موضوع مورد توجه پژوهشگران زیادی قرار گرفته، اما روش‌های ارائه شده برای حل مساله معمولا بار محاسباتی قابل توجهی دارند. از اینرو در این پژوهش از نگرشی جدید جهت حل مساله با استفاده از خاصیت تابع دلتای دیراک استفاده شده که روند حل مسأله را ساده‌تر و حجم محاسبات را به شدت کاهش میدهد. بر این اساس، ترک با رفتار دو طرفه به کمک تابع دلتای دیراک مدل شده است. این مدل با معرفی یک معیار مناسب، اثر بسته شدن ترک روی رفتار خمشی ستون را در نظر می‌گیرد. این معیار بسته به علامت کرنش محوری و همچنین یک یا دو طرفه بودن ترک، به هر ترک اجازه میدهد که باز یا بسته باشد. از روش پیشنهادی به منظور یافتن بار کمانشی، اثرات سختی ترک به ازای موقعیت‌های مختلف در دو حالت یک و دو ترکه و همچنین تاثیر باز و بسته شدن ترک روی بار کمانشی استفاده شد . به منظور صحت‌سنجی روابط تحلیلی به دست آمده از نرم‌افزار اجزای محدود SAP2000 بهره گرفته شد. پرونده مقاله
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