Sharif Digital Repository

The J-integral, as a powerful tool in fracture mechanics, is used to analysis of fracture behavior of materials. In order to, evaluate of three dimensional J-integral, an integral evaluation of line and surface is required. However, because surface integral evaluation requires the calculation of the second derivative of displacement field, an commercial finite element codes cannot calculate it.In this thesis, a method for computing 3D J-integral is presented using finite element analysis. In the analysis, the second derivative evaluation of displacement field is employed. In this method, error-minimal points for stress computation are not suitable for second derivative displacement... 

The so-called moving least square reproducing kernel method (MLSRKM), which is a meshfree Galerkin method, has two special properties in comparison with its prior version, say moving least square method (MLSM): (i) stability in preserving completeness conditions to the desired order for a discrete reproducing formula due to implementation of shifted and scaled basis, (ii) use of more accurate quadrature weights in a discrete reproducing form, especially along boundaries. However, because of employing shifted basis in MLSRKM, some of enrichment techniques, specifically in the context of linear elastic fracture mechanics (LEFM) problems, cannot be applied to this method. Therefore, we are... 

In this study, Interfacial crack is modeled by the extended finite element method (XFRM) in order to evaluate the stress intensity factors for interface crack problems. These problems have crack edge discontinuity, material interfaces and singularity at the crack tip, which is inappropriate to finite element (FEM) mesh. Furthermore, around crack tips and interface edge, extremely fine discretization is required to achieve reasonable accuracy. All these factors increase the time and cost of the FEM solution. Recently the extended finite element method is developed and applied to interface fracture problems. In the XFEM, special enrichment functions are added to the finite element displacement... 

Small punch test is an efficient technique to determine mechanical properties of large as well as small industrial parts. In this method a steel ball puncher with small radius, penetrate to the workpiece under certain displacement. Properties of the sample are detemined by measuing of force and obtaine the load-displacement diagram. In this study, small punch test was used to determine mechanical and fracture properties of 1.4841 steel. For these purpose small punch test was simulated by using finite element method, and exprimental small punch test was also done for mention steel which was under hydrogen embritment and creep due to working conditions. Afterward, exprimental results were... 

In the present work, the beginning and progressive growth of delamination in laminated composites plates has been studied. Interlaminar stresses at free edge of laminate may give rise to edge delamination and result in failure of laminate. So we need to determine the exact interlaminar stresses to predict the failure of laminated composites. A computer code based on layerwise theory that can obtain the exact interlaminar stresses been developed. Comparison between the present study and finite element software result showed the good agreement.A fracture mechanics approach is used to analysis delamination propagation between layers of composites laminate. In this approach damage propagation... 

Studying the failure mechanics of FGM materials is inevitable due to the increasing use of these materials in various industries. Stress intensity factor and integral-J are important parameters in fracture mechanics. Due to the fragile nature of ceramic components in FGM During the processing of these types of composite materials, cracks are encouraged. Therefore, crack analysis is inevitable in optimizing the design, reliability and durability of FGM materials and structures in innovative engineering applications. In this research, transverse crack growth in beams made of FGM materials has been investigated. First, a MATLAB code was prepared to extract the mechanical properties of these...