چكيده به لاتين
In recent years, the meshless methods have been developed in fracture mechanics field. These methods, reduce the time which is needed for modeling of structures. because there is no need for element creation. Besides this matter, some advantages like high accuracy in computation of stresse and strains specially in stress raiser areas e.g. at the vicinity of the crack tip, getting smooth stresses and strains and crack growth simulation with no need to remeshing, caused that the researchers tend to this methods in solving fracture mechanics problems.
In this thesis, a meshless code has been developed for two dimensional stress analysies of cracked bodies under creep condition. The results obtained by the developed code are validated by a creep testing machine, equipped with crack growth measurement facilities.
For evaluation of the developed meshless code, some examples are solved including investigation of Stress Concentration Factor in a plate with circular hole, investigation of Stress Concentration Factor in a plate with elliptical hole and investigation of Notch Shape Factor in the V-notched Brazilian Disc. Then a new criterion is proposed for simulation of crack discontinuity. In fact, in this criterion, a combination of the visibility method and the surrounding triangles method is used for determination of support domain. The advantage of the proposed criterion in comparison with the common criteria in the meshless methods, is that by using the connectivity concept in the Finite Element Method and by combination of two mentioned methods, the support domain for the nodes and the integration points near the crack faces is modified without any special mathematical formulation for the weight function paremeter. After that, by using the Initial Strain Method, creep analysis is done in the Element Free Galerkin method. In the next step, the dimenless h1 function which is the most important parameter in the C* integral, is determined for the standard test specimens and is compared with the Kumar relationships. Then in the next step, C* parameter is estimated by implementing Elastic Modulus Reduction (EMR) approach in the reference stress method and it is shown that this is an over estimate procedure and therefore is usefull for design purposes. In the last step, high temperature tests are performed for A286 superalloy at 650c for validation of the results obtained in the previous sectons. The performed tests includes determination of the fracture toughness and the determination of the C* parameter. In the section that the C* parameter is determined, the obtained results are compared with the related relationships and it is concluded that the tested specimens are close to the plane stress condition.
