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دسترسی آزاد مقاله
1 - Multiple Moving Cracks in a Non-Homogeneous Orthotropic Plane
R Bagheri S. M HosseiniIn this paper, a theoretical study of the behavior of multiple moving cracks in a non-homogeneous orthotropic plane under anti-plate deformation is presented. Material properties of the functionally graded (FG) orthotropic plane are assumed to vary exponentially in the چکیده کاملIn this paper, a theoretical study of the behavior of multiple moving cracks in a non-homogeneous orthotropic plane under anti-plate deformation is presented. Material properties of the functionally graded (FG) orthotropic plane are assumed to vary exponentially in the y-direction. First, the distributed dislocation method is used to perform stress analysis, and the Galilean transformation is used to express the wave equations in terms of the coordinates attached to the moving crack. Then, the solution of the moving screw dislocation in the non-homogeneous orthotropic plane is obtained using the Fourier transform and shows that the stress components have the familiar Cauchy singularity at the location of dislocation. The solution is employed to derive integral equations for a non-homogeneous orthotropic plane weakened by multiple moving cracks. Numerical calculations are performed to show the effects of material properties and the cracks propagating velocity on the dynamic stress intensity factors of crack tips پرونده مقاله -
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2 - Evaluating the Effects of Overload and Welding Residual Stress in Fatigue Crack Propagation
Ali Moarefzadeh Shahram Shahrooi Mehdi Jalali AzizpourIn this paper, a suitable method is presented to predicate fatigue crack propagation for cyclic loading with overload in residual stresses field resulted by weld. For this, first effective stress intensity factor (SIF) and effective cycle ratio (R) are introduced as fun چکیده کاملIn this paper, a suitable method is presented to predicate fatigue crack propagation for cyclic loading with overload in residual stresses field resulted by weld. For this, first effective stress intensity factor (SIF) and effective cycle ratio (R) are introduced as function depending on SIFs resulted by external load, weld residual stress and overload. Weight function is applied to calculate SIF resulted by weld residual stress. Also, a method is introduced to determine overload SIF and overload stress ratio. Then fatigue crack propagation equation is modified for our purpose. In other words, a simple and efficient method is presented in this paper for predicting fatigue crack propagation rate in welded joints when the overload is happen. Finally for evaluating this modified equation, experimental methods are applied. Test samples were M(T) geometry made of aluminum alloy with a longitudinal weld by the Gas Tungsten arc welding process. Modified equation has a good agreement with the experimental model presented in this field. پرونده مقاله -
دسترسی آزاد مقاله
3 - Fatigue Crack Growth in Thin-Wall Pipes Subjected to Bending
MohammadMahdi AmiriIn this paper, a circumferential external surface flaw in a metallic round pipe under cyclic bending loading is considered. Because of very rapid changes in the geometrical parameters around the crack front region, the mesh generation of this region must be done with gr چکیده کاملIn this paper, a circumferential external surface flaw in a metallic round pipe under cyclic bending loading is considered. Because of very rapid changes in the geometrical parameters around the crack front region, the mesh generation of this region must be done with great care. The analysis of the fatigue crack growth is done in accordance with Paris law. The spread lane of the exterior defect is achieved from the graph of “α” vs. “relative crack depth”. The growth of fatigue crack is also analyzed (the comparative crack depth against loading runs diagram) with various initial crack “α” beneath periodic loading. Fatigue shape growth of primarily semi-elliptical peripheral surface flaws is shown. The weight of the Paris exponent (material constant) on fatigue crack propagation is presented as well. Furthermore, the “fatigue crack growth” progression of several specimens is evaluated experimentally by employing a manually-constructed experimental setup. Conclusively, the experimental results achieved by periodic bending loading tests are compared with the numerical results. Fatigue shape development of initially semi-elliptical external surface defects is illustrated. The effect of the Paris exponent (material constant) on fatigue crack propagation is shown as well. Moreover, the fatigue crack growth of several specimens is assessed experimentally using a manually-constructed experimental set up. Finally, the experimental results obtained by cyclic bending loading tests are compared. پرونده مقاله -
دسترسی آزاد مقاله
4 - Studying the Effect of Pulse Shape on Dynamic Stress Intensity Factor at the Finite Crack Tip using Displacement Fields
Hossein Rahmani Mohammad Ahmadi BalootakiIn analytical studies, step (Heaviside) function is used to simulate an impact load. However, in real behaviour of materials, loading and unloading take a short time. The present study discusses analytically the effects of pulse shape and rising time of an impact load o چکیده کاملIn analytical studies, step (Heaviside) function is used to simulate an impact load. However, in real behaviour of materials, loading and unloading take a short time. The present study discusses analytically the effects of pulse shape and rising time of an impact load on dynamic stress intensity factor. Firstly, a pulse load with positive slip (linear and non-linear) is applied on a cracked plate and the amount of dynamic stress intensity factor on the crack tip is obtained. Then the effects of pulse time are discussed. Results show that increasing the rise time decreases the stress intensity factor because of reduction of inertia effects. Moreover, the duration of rise time plays the main role in dynamic stress intensity factor changes and how the variations are not matter. پرونده مقاله -
دسترسی آزاد مقاله
5 - Evaluation of Mixed-Mode Center Crack SIF in a Curved Plate Repaired by Stop Holes, Composite Patch, and Hybrid Methods
Sirvan Mohammadi sadegh daryaeiIn this research, using the 3D finite element method and considering different materials for a composite patch, the effect of separate and simultaneous use of stop holes and composite patch (one-sided and two-sided) on reduction of SIF in a curved plate including mixed- چکیده کاملIn this research, using the 3D finite element method and considering different materials for a composite patch, the effect of separate and simultaneous use of stop holes and composite patch (one-sided and two-sided) on reduction of SIF in a curved plate including mixed-mode crack is investigated. Glass-epoxy, graphite-epoxy, carbon-epoxy, and boron-epoxy are used for repair patches. For the one-sided patch, the effects of different geometric parameters on the efficiency of the repair are investigated. For all four composite patches, as the thickness of the patches increases, KI and KII decrease, but with increasing the patch length, KI and KII increase. The research results also show that with increasing the width of the glass-epoxy patch, KI and KII almost do not change, but for other patches, as the patch width increases, the SIF increases. The effect of the radius of curvature of the plate on the efficiency of various repair methods is also investigated. In all repair methods studied, SIF decreases with increasing radius of curvature of the curved plate. Different repair methods are compared and the best method with the highest efficiency is introduced. The best repair mode is the hybrid repair method (stop-holes and two-sided boron-epoxy patch), which reduces KI and KII by 84.50 and 86.6%, respectively. Finally, the effect of adhesive thickness used for patch bonding on hybrid repair method efficiency and durability is investigated. for all four materials of patches understudy, KI and KII increase with increasing the thickness of the adhesive, but on the other hand, as the thickness of the adhesive increases, the maximum Von Mises stress in the adhesive decreases. پرونده مقاله -
دسترسی آزاد مقاله
6 - Removing Residual Stress and Increasing Fatigue Life by Ultrasonic Method
Ali MoarefzadehIn this paper, a new method is introduced for evaluating effects of residual stress on fatigue life. The ability of ultrasonic method using longitudinal wave with critical angle of refraction or LCR wave in measuring and removing residual stresses due to welding was use چکیده کاملIn this paper, a new method is introduced for evaluating effects of residual stress on fatigue life. The ability of ultrasonic method using longitudinal wave with critical angle of refraction or LCR wave in measuring and removing residual stresses due to welding was used. Two plates of alloy 2024-T351 were welded to each other. To measure their residual stress field acoustoelastic property was used and the changes in the speed of ultrasonic propagation of elastic waves when passing through the residual stress fields was investigated. In order to exert the effects of residual stress on fatigue life, the relations between the coefficients of effective stress intensity (SIF) and Fatigue Crack Propagation (FCP) rate in a state that the parts were welded together with residual stress under cyclic loading were obtained. Finally, ultrasonic waves with a certain frequency were used to remove the residual stresses. Also, the relationships between stress intensity factor and fatigue crack propagation rate were modified to predict fatigue life after removal of residual stresses. This method resulted in a 31% increase in fatigue life. The main reason for the increase in life was the plastic area created by the ultrasound wave. Therefore, it can be said that introduced method are suitable for using to remove residual stress due to welding. پرونده مقاله -
دسترسی آزاد مقاله
7 - Moving Three Collinear Griffith Cracks at Orthotropic Interface
P Mandal S.C MandalThis work deals with the interaction of P-waves between a moving central crack and a pair of outer cracks situated at the interface of an orthotropic layer and an elastic half-space. Initially, we considered a two-dimensional elastic wave equation in orthotropic medium. چکیده کاملThis work deals with the interaction of P-waves between a moving central crack and a pair of outer cracks situated at the interface of an orthotropic layer and an elastic half-space. Initially, we considered a two-dimensional elastic wave equation in orthotropic medium. The Fourier transform has been applied to convert the basic problem to solve the set of four integral equations. These set of integral equations have been solved to to get the analytical expressions for the stress intensity factor (SIF) and crack opening displacements (COD) by using the finite Hilbert transform technique and Cooke’s result. The main objective of this work is to investigate the dynamic stress intensity factors and crack opening displacement at the tips of the cracks. The aims of the study of these physical quantities (SIF, COD) is the prediction of possible arrest of the cracks within a certain range of crack velocity by monitoring applied load. SIF and COD have been depicted graphically for various types of orthotropic materials. We presented a parametric study to explore the influence of crack growing and propagation. This result is very much applicable in bridges, roads, and buildings fractures. پرونده مقاله -
دسترسی آزاد مقاله
8 - Analytical Stress Solutions of an Orthotropic Sector Weakened by Multiple Defects by Dislocation Approach
A.R Hassani A HassaniIn this article, the anti-plane deformation of an orthotropic sector with multiple defects is studied analytically. The solution of a Volterra-type screw dislocation problem in a sector is first obtained by means of a finite Fourier cosine transform. The closed form sol چکیده کاملIn this article, the anti-plane deformation of an orthotropic sector with multiple defects is studied analytically. The solution of a Volterra-type screw dislocation problem in a sector is first obtained by means of a finite Fourier cosine transform. The closed form solution is then derived for displacement and stress fields over the sector domain. Next, the distributed dislocation method is employed to obtain integral equations of the sector with cracks and cavities under anti-plane traction. These equations are of Cauchy singular kind, which are solved numerically by generalizing a numerical method available in the literature by means of expanding the continuous integrands of integral equations with different weight functions in terms of Chebyshoff and Jacobi polynomials. A set of examples are presented to demonstrate the applicability of the proposed solution procedure. The geometric and force singularities of stress fields in the sector are also studied and compared to the earlier reports in the literature. پرونده مقاله -
دسترسی آزاد مقاله
9 - Analytical Solutions of Finite Wedges Coated by an Orthotropic Coating Containing Multiple Cracks and Cavities
A AjdariThis paper presents a general formulation for an isotropic wedge reinforced by an orthotropic coating involving multiple arbitrarily oriented defects under out of plane deformation. The exact closed form solution of the problem weakened by a screw dislocation in the iso چکیده کاملThis paper presents a general formulation for an isotropic wedge reinforced by an orthotropic coating involving multiple arbitrarily oriented defects under out of plane deformation. The exact closed form solution of the problem weakened by a screw dislocation in the isotropic wedge is obtained by making use of finite Fourier cosine transform. Also, the closed-form solutions of the out of plane stress and displacement fields are obtained. After that, by making use of a distributed dislocation approach, a set of singular integral equations of the domain involving smooth cavities and cracks subjected to out of plane external loading are achieved. The cracks and cavities are considered to be only in the isotropic wedge. The presented integral equations have Cauchy singularity and must be evaluated numerically. Multiple numerical examples will be presented to show the applicability and efficiency of the presented solution. The geometric and point load singularities of the stress components are obtained and compared with the available data in the literature. پرونده مقاله -
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10 - Three-Dimensional Stress Analysis for Semi-Elliptical Cracks in the Connection of Cylinder-Hemispherical Head for Thick-Walled Cylindrical Pressure Vessels
H Eskandari M Ghanbari F MirzadehThese pressure vessels are made by different type of heads. One of them is hemi-spherical head. The area of geometrical discontinuity, like the connection of the cylinder to its hemi-spherical head, are the most susceptible areas for crack initiation along their welds. چکیده کاملThese pressure vessels are made by different type of heads. One of them is hemi-spherical head. The area of geometrical discontinuity, like the connection of the cylinder to its hemi-spherical head, are the most susceptible areas for crack initiation along their welds. So it is worthwhile to consider cracks located at this connection. The purpose of this article is to investigate the effect of variation of stress field and geometry of problem on distribution of Stress Intensity Factor (SIF) for a semi-elliptical surface crack which is located at the connection of cylinder to its hemispherical head. The three dimensional finite element analysis is performed by employing singular elements along the crack front. The ratio of crack depth to crack length (a/c) ranged from 0.3 to 1.2; the ratio of crack depth to wall thickness (a/t)ranged from 0.2 to 0.8; and the cylinder geometry parameter of vesselranged from 1.2 to 2. For better comparison the results are normalized and reported in non-dimensional formats. The results show that the crack configuration, vessel thickness and radius have significant influence on the stress intensity factor distribution along the crack front. Also For a fixed and the maximum value of SIF occur in the cylindrical part and approximately near the deepest point of crack; not on the deepest point of crack depth and this may be due to changing stress field in this connection. The stress intensity factors are presented in suitable curves for various geometrical configurations providing useful tool for the fracture mechanics design of cracked pressure vessels. پرونده مقاله -
دسترسی آزاد مقاله
11 - Investigating Stress Intensity Factor and Fatigue Life Using Extended Isogeometric Analysis Based on Bézier Extraction of NURBS
M. M Shoheib Sh Shahrooi M Shishehsaz M HamzeheiIn this paper, the extended isogeometric analysis based on Bézier extraction of NURBS is applied for Investigating stress intensity factor and fatigue life in the two-dimensional crack problems with thermal and mechanical cyclic loading. By transforming NURBS fun چکیده کاملIn this paper, the extended isogeometric analysis based on Bézier extraction of NURBS is applied for Investigating stress intensity factor and fatigue life in the two-dimensional crack problems with thermal and mechanical cyclic loading. By transforming NURBS function to linear combination of Bernstein functions defined over C0-continuous Bézier elements, the extended isogeometric analysis can be implemented in the extended finite element method framework. Grid points around the crack line and crack tip are identified by the level set representation. Then, discontinuous enrichment functions are added to the isogeometric analysis approximation. Thus, this method does not require remeshing. The interaction integral method and Paris law has been used to extract stress intensity factor and evaluate fatigue life, respectively. Numerical examples are examined to validate the efficiency of the proposed method. The effect of adaptive refinement strategies on computational cost and convergence is studied. Numerical examples showed that the presented method produces highly accurate results, yet it is beneficial to implement. پرونده مقاله -
دسترسی آزاد مقاله
12 - Evaluation of Stress Intensity Factor in a Center Cracked Curved Plate Repaired with Stop Holes, Composite Patch, and Hybrid Methods
S Mohammadi S DaryaeiStop holes and composite patches are the most important methods used to repair cracked plates. In this research, using a 3D finite element method and considering different materials for a composite patch, the effect of separate and simultaneous use of stop holes and com چکیده کاملStop holes and composite patches are the most important methods used to repair cracked plates. In this research, using a 3D finite element method and considering different materials for a composite patch, the effect of separate and simultaneous use of stop holes and composite patch (one-sided and two-sided) on the reduction of SIF in a cracked curve plate is investigated. The best position and arrangement of crack stop holes and the best dimensions and material used for the composite patch are determined. Then, the effect of the radius of curvature of the plate on the efficiency of various repair methods is investigated. The results show that with increasing the radius of curvature of the plate, the SIF value decreases in all repair methods and the efficiency of the patch improves in the cases of using the patch or the hybrid method. Besides, from the radius of curvature of approximately 5 meters onwards, a further increase in the radius of curvature does not affect the efficiency of various repair methods. Simultaneous use of the graphite-epoxy double-sided patch and stop holes reduces SIF by 79.9% compared to unrepaired condition. پرونده مقاله -
دسترسی آزاد مقاله
13 - Effect of Boundary Condition on Pre-Existing Crack Under Fatigue Loading
V.K Singh P.C Gope R.K BhagatIn this paper, the present investigation has been conducted keeping in mind some of the problems concerning the crack propagation direction and growth under constant loading in an inclined crack geometry. The present studies mainly focused on the development and modific چکیده کاملIn this paper, the present investigation has been conducted keeping in mind some of the problems concerning the crack propagation direction and growth under constant loading in an inclined crack geometry. The present studies mainly focused on the development and modifications in the crack growth criterion to account the biaxial, shear loading and number of stress terms. Existing criteria for the prediction of crack initiation direction have been modified taking higher order stress terms. The effective methods of experimentally determining the stress intensity factor for a body containing a crack is to analyze the isochromatic pattern obtained from a photoelastic model. The effect of biaxial load factor, crack angle, Crack length/width of specimen and length of specimen/width of specimen were studied and a regression model was developed for geometry correction to predict stress intensity factor for tearing mode and intensity factor for shearing mode. This approach is being used to predict crack growth trajectory under biaxial cyclic loading by assuming that the crack may grow in a number of discrete steps using the vectorial method. MTS criterion (Maximum Tangential Stress criterion) is used for prediction of crack initiating angle. The crack growth trajectory has been determined by cycle simulation procedure. پرونده مقاله -
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14 - 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 چکیده کاملPresent 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. پرونده مقاله -
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15 - Photoelastic Determination of Mixed Mode Stress Intensity Factors
V.K Singh P.C GopeA two dimensional finite model with inclined crack at different crack angles are being analyzed in mixed mode condition using photo elasticity method for the determination of Stress Intensity Factors. The well-known Sih’s equation and three points deterministic ap چکیده کاملA two dimensional finite model with inclined crack at different crack angles are being analyzed in mixed mode condition using photo elasticity method for the determination of Stress Intensity Factors. The well-known Sih’s equation and three points deterministic approach is used for the determination of stress intensity factors. The effects of biaxial load factor, crack angle, size factors were studied and a regression model was developed for geometry correction to predict Stress Intensity Factors. The results give a good compromise to the theoretical one. The experimental result also gives significant data for the two dimensional mixed mode loading conditions. پرونده مقاله -
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16 - Fracture Analysis of Externally Semi-Elliptical Crack in a Spherical Pressure Vessel with Hoop-Wrapped Composite
H Eskandari Gh Rashed F MirzadeIn this paper the effect of composite hoop-wrapped on stress intensity factor for semi-elliptical external crack which located in spherical pressure vessel, were investigated through the Finite Element Analysis. In order to find the effect of some parameters such as com چکیده کاملIn this paper the effect of composite hoop-wrapped on stress intensity factor for semi-elliptical external crack which located in spherical pressure vessel, were investigated through the Finite Element Analysis. In order to find the effect of some parameters such as composite thickness and width, internal pressure and crack geometry, comparisons between different cases were done and discussed in detail. The result show that repairing crack with composite hoop-wrapped, can significantly reduce the stress intensity factor along the crack front. پرونده مقاله -
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17 - Analysis of Mode III Fraction in Functionally Graded Plate with Linearly Varying Properties
M.R TorshizianA model is provided for crack problem in a functionally graded semi-infinite plate under an anti-plane load. The characteristic of material behavior is assumed to change in a linear manner along the plate length. Also the embedded crack is placed in the direction of the چکیده کاملA model is provided for crack problem in a functionally graded semi-infinite plate under an anti-plane load. The characteristic of material behavior is assumed to change in a linear manner along the plate length. Also the embedded crack is placed in the direction of the material change. The problem is solved using two separate techniques. Primary, by applying Laplace and Fourier transformation, the governing equation for the crack problem is converted to the solution of a singular integral equation system. Then, finite element technique is employed to analyze this problem by considering quadrilateral eight nodded singular element near the crack tips. The effects of material non-homogeneity and crack length on the stress intensity factor are studied and the results of two methods are judged against each other. پرونده مقاله -
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18 - Thermoelastic Fracture Parameters for Anisotropic Plates
S Kebdani A Sahli S SahliThis paper deals with the determination of the effect of varying material properties on the value of the stress intensity factors, KI and KII, for anisotropic plates containing cracks and subjected to a temperature change. Problems involving cracks and body forces, as w چکیده کاملThis paper deals with the determination of the effect of varying material properties on the value of the stress intensity factors, KI and KII, for anisotropic plates containing cracks and subjected to a temperature change. Problems involving cracks and body forces, as well as thermal loads are analysed. The quadratic isoperimetric element formulation is utilized, and SIFs may be directly obtained using the ‘traction formula’ and the ‘displacement formula’. Three cracked plate geometries are considered in this study, namely: (1) a plate with an edge-crack; (2) a plate with a double edge-crack; (3) a plate with symmetric cracks emanating from a central hole. Where appropriate, finite element method (FEM) analyses are also performed in order to validate the results of the BEM analysis. The results of this study show that, for all crack geometries, the mode-I stress intensity factor, K∗I decreases as the anisotropy of the material properties is increased. Additionally, for all these cases, K∗I decreases as the angle of orientation of the material properties, , increases with respect to the horizontal axis. The results also show that BEM is an accurate and efficient method for two-dimensional thermoelastic fracture mechanics analysis of cracked anisotropic bodies. پرونده مقاله -
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19 - Edge Crack Studies in Rotating FGM Disks
H EskandariThis article focused on the stress analysis of an edge crack in a thin hallow rotating functionally graded material (FGM) disk. The disk is assumed to be isotropic with exponentially varying elastic modulus in the radial direction. A comprehensive study is carried out f چکیده کاملThis article focused on the stress analysis of an edge crack in a thin hallow rotating functionally graded material (FGM) disk. The disk is assumed to be isotropic with exponentially varying elastic modulus in the radial direction. A comprehensive study is carried out for various combinations of the crack length and orientation with the different gradation of materials. The effect of non-uniform coefficient of thermal expansion on the distribution of stress intensity factor is also studied. The results which are normalized for the advantage of non-dimensional analysis show that the material gradation, the crack orientation and the crack length have significant influence on the amount of stress intensity factors. پرونده مقاله -
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20 - 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 چکیده کاملThis 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. پرونده مقاله -
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21 - تعیین ضریب شدت تنش در ورق با ترک میانی با استفاده از روش هم هندسی براساس عملگر بیزییر تحت بارگذاری کوپله حرارتی و مکانیکی
محمد مهدی شهیب پیمان یوسفیدر این تحقیق، هدف تعیین ضریب شدت تنش در یک ورق ترک دار تحت بارگذاری حرارتی و مکانیکی است. برای این منظور به کمک کدنویسی در نرم افزارمتلب یک ورق با ترک میانی به روش هم هندسی بر اساس عملگر بیزییر، مدل سازی و المان بندی گردید. در این روش توابع پایه نربز با استفاده از عمل چکیده کاملدر این تحقیق، هدف تعیین ضریب شدت تنش در یک ورق ترک دار تحت بارگذاری حرارتی و مکانیکی است. برای این منظور به کمک کدنویسی در نرم افزارمتلب یک ورق با ترک میانی به روش هم هندسی بر اساس عملگر بیزییر، مدل سازی و المان بندی گردید. در این روش توابع پایه نربز با استفاده از عملگر بیزییر به صورت یک ترکیب خطی از چندجمله ای های برنشتاین تولید می شوند. استفاده از این عملگر موجب تولید المان های بیزییر با پیوستگی Co شده که چندجمله ای های برنشتاین بر روی این المان ها تعریف می شوند. جهت مدل سازی ترک از روش هم هندسی توسعه یافته استفاده شد. در این روش به کمک تعریف تابع مجموعه تراز مناسب، نقاط کنترلی که در طول ترک و نوک ترک وجود دارند شناسایی و استخراج شده اند. با غنی سازی نقاط کنترلی استخراج شده با توابع غنی ساز مناسب و اعمال شرایط مرزی، فرآیند تحلیل انجام شده و کرنش ها و تنش ها محاسبه گردیدند. در نهایت مقدار ضریب شدت تنش مد اول بر اساس روش انتگرال اندرکنش به دست آمد. برای بررسی صحت نتایج به دست آمده، تحلیل مشابهی به روش اجزا محدود انجام شد و نتایج حاصل از هر دو روش مقایسه شد. پرونده مقاله -
دسترسی آزاد مقاله
22 - ارزیابی تاثیر ثوابت ناهمگنی مواد بر ضرایب شدت تنش در ورق پیزوالتریک مدرج تابعی با استفاده از روش بدون المان پتروف گالرکین محلی(MLPG)
محمد معدل شهرام شهروئیدر این مقاله از روش بدون المان پتروف گالرکین محلی برای به دست آوردن ضریب شدت تنش در ورق پیزو الکتریک مدرج تابعی تحت بارگذاری کششی یکنواخـت استفاده شده است. جهت مدل سازی میدان جابجایی و تنش، اطراف نوک ترک از روش مشاهده پذیری و اضافه نمودن گره ها و غنی سازی توابع پایه به چکیده کاملدر این مقاله از روش بدون المان پتروف گالرکین محلی برای به دست آوردن ضریب شدت تنش در ورق پیزو الکتریک مدرج تابعی تحت بارگذاری کششی یکنواخـت استفاده شده است. جهت مدل سازی میدان جابجایی و تنش، اطراف نوک ترک از روش مشاهده پذیری و اضافه نمودن گره ها و غنی سازی توابع پایه به دلیل وجود تکینگی اطراف نوک بهره گرفته شده است. همچنین از مدل تابع نمایی برای بیان تغییرات خواص جنس ماده پیزوالکتریک استفاده گردید. سپس میدان های جابجایی و پتانسیل الکتریکی تولید شده در اثر بارگذاری مکانیکی و تنش ها به ازای ثوابت ناهمگنی جنس متفاوت ماده پیزوالکتریک مدرج تابعی در راستاهای متفاوت ورق تنش از روش بدون المان محاسبه و با نتایج حاصل از نرم افزار اجزا محدود کامسول مقایسه گردید. در نهایت ضرایب شدت تنش از روش بدون المان با نتایج از حل تحلیلی مقایسه گردید که انطباق قابل قبولی را نشان داده است. پرونده مقاله -
دسترسی آزاد مقاله
23 - بررسی خستگی و ضرایب شدت تنش و رشد ترک در چندلایه های GLARE
فرزاد امام علی زاده سید میثم حسینی محمد جعفر استاد احمد قرابیدر این تحقیق به بررسی ضرایب شدت تنش و رشد ترک در چندلایه های هیبریدی از جنس GALRE و مورد استفاده در صنایع هوافضا پرداخته شده است. چندلایه GLARE، آلومینیوم های تقویت شده با لایه های کامپوزیتی از جنس شیشه/اپوکسی هستند. در این پژوهش ابتدا پس از ایجاد ترک با طولهای مختلف در چکیده کاملدر این تحقیق به بررسی ضرایب شدت تنش و رشد ترک در چندلایه های هیبریدی از جنس GALRE و مورد استفاده در صنایع هوافضا پرداخته شده است. چندلایه GLARE، آلومینیوم های تقویت شده با لایه های کامپوزیتی از جنس شیشه/اپوکسی هستند. در این پژوهش ابتدا پس از ایجاد ترک با طولهای مختلف در لایه های آلومینیوم، با استفاده از روش اجزای محدود به محاسبه ضرایب شدت تنش در لایه های آلومینیوم پرداخته شد. سپس با استفاده از رابطه پاریس رشد ترک چندلایه های هیبریدی مورد بررسی قرار گرفت. نتایج بدست آمده نشان می دهد که ضرایب شدت تنش در لایه های آلومینیوم مجزا، بسیار بیشتر از لایه های آلومینیوم موجود در چندلایه های هیبریدی است و در نتیجه رشد ترک در آنها سریعتر اتفاق می افتد. پرونده مقاله -
دسترسی آزاد مقاله
24 - تخمین مسیر رشد ترک مورب در صفحه سوراخدار تحت بارگذاری چند محوره
کاظم رضاکاشی زادهدر مقاله حاضر، هدف اصلی مشخص نمودن مسیر رشد ترک مورب در صفحه سوراخ دار تحت بارگذاری چند محوره است. بدین منظور یک صفحه مستطیلی شکل که دارای یک سوراخ مربعی در وسط آن میباشد، در نظر گرفته شده است. در گوشه سمت راست بالای این سوراخ، ترک اولیه ای به طول 5 میلیمتر و زاویه 55 چکیده کاملدر مقاله حاضر، هدف اصلی مشخص نمودن مسیر رشد ترک مورب در صفحه سوراخ دار تحت بارگذاری چند محوره است. بدین منظور یک صفحه مستطیلی شکل که دارای یک سوراخ مربعی در وسط آن میباشد، در نظر گرفته شده است. در گوشه سمت راست بالای این سوراخ، ترک اولیه ای به طول 5 میلیمتر و زاویه 55 درجه در جهت پادساعتگرد وجود دارد. با استفاده از نرم افزار المان محدود آباکوس ضریب شدت تنش ترک در مودهای شکست اول و دوم بدست آمده و در پی آن با محاسبه شدت تنش معادل، زاویه رشد ترک در مرحله بعدی به روش ماکزیمم تنش محیطی بدست آمده است. این روند تا شکست کامل قطعه و یا از کارافتادگی آن ادامه یافته است. پرونده مقاله -
دسترسی آزاد مقاله
25 - Cracks Analysis in Zavin Concrete Dam Using Fracture Mechanics Approach
Hossein Rezaee Azariani Mohammad Reza Esfahani keivan bina Soheil GharehMost of the existing concrete dams are subjected to cracking. These cracks are caused by various factors such as construction practices, curing, loads and volume change of mass concrete which reduce the efficiency, failure or instability of concrete dams. Using fracture چکیده کاملMost of the existing concrete dams are subjected to cracking. These cracks are caused by various factors such as construction practices, curing, loads and volume change of mass concrete which reduce the efficiency, failure or instability of concrete dams. Using fracture mechanics as a new method to estimate stability and durability of concrete dams is recommended in scientific publications in worldwide. This study aimed to apply the principles and criteria of linear elastic fracture mechanics to evaluate the propagation of cracks in body and foundation of Kalat concrete gravity dam -that is located in the northern province of Khorasan Razavi, Iran- subjected to the worst-case loading, including the extraordinary loading case due to earthquake with full reservoir. For this purpose, ZENCRACK-v 7.7 and ABAQUS-v 6.10.1 software were utilized and nonlinear analysis of finite element are performed. Subsequently, linear elastic fracture mechanics criteria including stress intensity factor and maximum circumferential stress were calculated for existing cracks in various parts of dam body and foundation and stability of initial cracks, kinking angle and extension of them were determined. Based on the obtained results, crack propagation in areas near to both dam abutments is investigated. To do so, a plain strain condition is assumed that only expanded in longitudinal and transverse axes, but with being away from abutments toward dam center, crack growth logged from plain strain condition and expanded in the vertical direction. Also, under earthquake load with 10 second duration, maximum tension and compression stress were occurred between 2.32 to 4.26 seconds. پرونده مقاله -
دسترسی آزاد مقاله
26 - 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 چکیده کاملConical 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. پرونده مقاله -
دسترسی آزاد مقاله
27 - Investigating the Effect of Residual Stress on Fatigue Crack Propagation by Modified J-integral and Experimental Method
Ali Moarrefzadeh Shahram ShahrooiThis paper is introduced new method for predicting of fatigue crack propagation (FCP) in residual stress (RS) field due to welding. If there is stress in the material and is subjected to loading, the effects of loading and RS must be considered simultaneously. For this چکیده کاملThis paper is introduced new method for predicting of fatigue crack propagation (FCP) in residual stress (RS) field due to welding. If there is stress in the material and is subjected to loading, the effects of loading and RS must be considered simultaneously. For this purpose, stress intensity factor (SIF) in liner elastic fracture mechanics (LEFM) approach and J-integral in elastic-plastic fracture mechanics (EPFM) approach are used. The superposition principle based on LEFM is used to consider the RS effects on the cycle ratio and SIF. To achieve more appropriate results based on EPFM, the J-integral is modified to consider the simultaneous effects of RS and external loading. Finally, the FCP equations are modified to consider into calculation the simultaneous influences of RS and cyclic loading. Results from FCP equation based on J-integral are in good agreement with experimental results. The obtained results show that the MLPG method is suitable for calculating the residual stress and the modified J-integral method is the best method for predicting FCP in the RS field caused by welding. پرونده مقاله -
دسترسی آزاد مقاله
28 - Stress Field Analysis of V-Notches with Tip Cracks in a Polymer Material Using Digital Image Correlation
ن. سلطانی م.ر. یادگاری ا. اشراقیIn this study, displacement field around v-notches of a poly methyl metha crylate (PMMA) specimen with tip cracks will be analyzed using digital image correlation technique. First intensity factor in combination with in-plane rigid body translations and rotation compone چکیده کاملIn this study, displacement field around v-notches of a poly methyl metha crylate (PMMA) specimen with tip cracks will be analyzed using digital image correlation technique. First intensity factor in combination with in-plane rigid body translations and rotation components will be determined by linear least squares fitting of the displacement field data to the corresponding relations among stress intensity factor and displacement field. The effect of v-notch angle on the results would be investigated. Experimental results will be compared with those obtained from finite element analysis. Good consistency is shown to exist between the results of two methods. The existence and a measure of a small region (corresponding to the plastic deformation zone in front of the crack tip) is demonstrated which should be excluded in data extraction for digital image correlation post-processing using linear elastic fracture mechanics relations. پرونده مقاله -
دسترسی آزاد مقاله
29 - The mixed mode fracture mechanics in a hole plate bonded with two dissimilar plane
محمد رحیم ترشیزیان حسین اندرزجوIn the present research, the mixed-mode fracture mechanics analysis in a plate with central hole under tensile loading is considered. It is assumed that a plate containing two symmetrical hole-edge cracks is bonded with two dissimilar planes. The stress intensity factor چکیده کاملIn the present research, the mixed-mode fracture mechanics analysis in a plate with central hole under tensile loading is considered. It is assumed that a plate containing two symmetrical hole-edge cracks is bonded with two dissimilar planes. The stress intensity factors at the crack tips are calculated. The problem is modeled in Casca software and this model is analyzed with Franc software. The effects of various factors such as hole diameter, crack length, angle of crack and material properties of plates have been investigated on stress intensity factors. The stress intensity factors increases with increasing crack length. Also, the stress intensity factors increases with the increase of hole diameter. For a certain amount of for small crack lengths the effect of cracks length on variation of stress intensity factors is more than the hole diameter but for large crack lengths the effect of hole diameter on variation of stress intensity factors is more than the cracks length. پرونده مقاله -
دسترسی آزاد مقاله
30 - Determination The Stress Intensity Factor in The Un-Central Edge Cracks With The concentrated Load
فرزاد فریبا سید مهران زحلیThe stress distribution on the tip of the cracks and the stress intensity factor on them are the main courses in the fracture mechanic. The stress intensity factor of the cracks with the different load exited and the different geometry are listed in the tables of the st چکیده کاملThe stress distribution on the tip of the cracks and the stress intensity factor on them are the main courses in the fracture mechanic. The stress intensity factor of the cracks with the different load exited and the different geometry are listed in the tables of the standard books. In all of them, the cracks are located in the central point of the plates. In the uniform edge loaded case, the crack position is not effect on the stress intensity factor of the crack but in the case that the load is concentrated the stress distribution different from point to another point and therefore the stress intensity factor of the crack, is changed with the crack displacement from the point of the exited load. In this paper, the stress intensity factor changes with the distance of it from the edge of the semi-infinite plate with the edge crack is investigated. A new relation is introduced from the simulation solution with the Abaqus. Then, similar relation from analytical solution from the theory of the linear fracture mechanic was proposed. This relation was determined from the stress distribution calculation in the plate with the pointed load with the analytical solution from the elasticity theory. This two relations were compared with another and finally the more accurate relation was introduced as the relation of the stress intensity factor with the distance from the edge of the plate. پرونده مقاله -
دسترسی آزاد مقاله
31 - 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 چکیده کاملIn 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. پرونده مقاله -
دسترسی آزاد مقاله
32 - 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
33 - 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
34 - Modeling and Crack-growth and Calculate First Intensity Factor with Ansys Software
S.M. Hossein MirgilaniStudy about Fracture Mechanics and the root cause of fracture in order to estimates lifetime for Mechanical parts in designing process and manufacturing have tremendous role in this realm. Stress intensity factor comes into design which not only is dependent to geometry چکیده کاملStudy about Fracture Mechanics and the root cause of fracture in order to estimates lifetime for Mechanical parts in designing process and manufacturing have tremendous role in this realm. Stress intensity factor comes into design which not only is dependent to geometry also extremely to load condition; for instance, it is important in failure processes (brittle and ductile Materials) or to predict rest life for a mechanical part under fluctuating stress. Stress intensity factor is separated from stress concentration factors. This dimensionless factor, is used to quantify how "concentrated" the stress is. Stress concentration factors are due to geometrical changes of cross sections and regardless of the load condition. At this article, concentrate on modeling and growing a crack during Tension Stress and calculate first stress intensity factor with Ansys software and compare the result with Westgard function پرونده مقاله
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