Numerical Simulation Of2D Crack Propagation And Fatigue Life Prediction

In engineering practice, a variety of microcracks inevitably exist in the components due to defects of the material itself or damage caused by the processing. Under certain conditions, microcracks will continue to expand, accumulate and result in the material fracture failure eventually. A large number of project accidents have shown that brittle fracture under low stress caused by initial crack propagation is the major failure mode for engineering structures. So it is of great practical and theoretical significance to study the law of crack growth and to analyze their fracture characteristics. Based on the theories of linear-elastic fracture mechanics, A special finite element program has been developed using ANSYS APDL to simulate crack propagation and predict fatigue life in2D solids. The main contents of this paper are as follows:1) The numerical calculating methods for stress intensity factors including displacement extrapolation, crack opening displacement and J integral are elaborated systematically aiming at singular stress field near the crack tip. A comparison and analysis has been carried out for above methods by introducing several typical samples. Meanwhile, The effects of crack length, geometric parameters and external load on the stress intensity factors are investigated.2) A specific analysis procedure based on the platform of ANSYS is programmed to simulate the crack growth path. Stress intensity factor is calculated for each step during the propagation and the crack propagation angle is determined using the maximum circumferential stress criterion. Crack model is then updated and automatically meshed according to the coordinates of the new crack tip until the condition in which crack will propagate unsteadily is met. The excellent agreement between numerical results and the analytical solutions or experimental observations shows the accuracy of the proposed algorithm.3) A fatigue life prediction model is set up adopting the Paris criterion with the equivalent stress intensity factor introduced in the crack growth analysis presented above. Numerical simulations for through-thickness cracks under constant amplitude loading are carried out with this model. The results are well in agreement with that of the references. Moreover, a shot peening residual stress field is formed by initial stress method and the influence of compressive residual stress on fatigue crack growth is discussed. The results show that the residual stress has obvious inhibitory effect on crack propagation. The influence of the compressive stress does not disappear immediately, instead, there is an influence domain when the crack tip pass over the compressive stress layer, with the increase of distance between crack tip and the compressive stress layer boundary the inhibition decreases gradually until it reaches zero.4) For the special failure mode of interfacial fracture in composites, the cohesive zone model (CZM) and the virtual crack closure technique are used to simulate interfacial debonding of double cantilever beam. The simulation result indicates that both methods produce good agreement with each other and are insensitive to the mesh size. However, the cohesive strength have a significant impact on the load-displacement curve.