Finite Element Simulation Of Fatigue Crack Growth Path Under Mixed Mode Ⅰ-Ⅱ Loading

Many types of mechanical equipment such as boilers, pipes and pressure vessels are subjected to multiaxial cyclic loading. The fracture induced by fatigue is one of the most common failure forms. Therefore, it is of great significance and worthy to study on the fatigue failure mechanism and fatigue crack growth behavior under multiaxial cyclic loading.The fatigue crack growth behavior under mixed mode I-II loading was investigated numerically by modeling the non-standard compact tension-shear specimens of16MnR steel. In order to obtain the accurate elastic-plastic stress-strain responses, the Armstrong-Frederick type cyclic plasticity model proposed by Jiang and Sehitoglu was used. This theoretical model can capture the cyclic plasticity characterization of16MnR steel and was implemented into Abaqus by the user subroutine UMAT. The upper and lower crack surfaces were set to be master and slave contact surfaces respectively to simulate the potential closure of fatigue crack. To consider the effect of the residual stress induced by fatigue crack growth, the dynamic crack propagation model was used in the finite element simulation. A multiaxial fatigue damage criterion based on the critical material plane was adopted to calculate the accumulated fatigue damage in order to consider the multiaxial loading condition.Based on the outputted elastic-plastic stress-strain results from finite element analysis, the stabilized stress-strain hysteresis loops were obtained. And then the position and orientation of fatigue initiation, the fatigue crack growth rate as well as the fatigue crack growth path were predicted by the unified model. It is obvious that the numerical results agree well with the experimental data.