Numerical Simulation Of The Effect Of Shot Peening Residual Stress On Crack Growth Fatigue Life

Generally there comes out micro cracks under cyclic loading in metal components, which results in degradation of material strength, stiffness and so on. Extending cracks come out when micro cracks accumulate to a certain extent, finally they cause fatigue fracture destruction. In engineering practice, most metal components work in the cyclic loading, and 80%-90% of the total destruction are caused by fatigue fracture according to statistics. Mastering the crack propagation rule and controlling the crack propagation is very important and necessary. How to prevent crack extending so as to avoid fatigue fracture failure and to improve the safety life, which has become an urgent problem to be solved for avoiding catastrophic accident. Based on fatigue fracture theory, with the help of software ABAQUS and the method of numerical simulation, the fatigue life of selected specimen is predicted and verified. On the basis of it, the effect of shot peening on fatigue life is discussed. The main research contents are as follows:(1)To predict the fatigue life of crack extension, energy release rate of the crack tip was calculated based on the virtual crack closure technique (VCCT), and crack growth was controlled by the fracture criterion. A stable response of low cycle fatigue under cyclic loading was obtained by direct cycle method. In order to accelerate the efficiency of calculation of low cycle fatigue, a interpolation technique was applied, which namely release at least one unit length at the crack tip after a certain cycles.(2)To predict the effect of shot peening on the fatigue life of crack propagation, the above method based on linear elastic fracture mechanics is no longer applicable. A new fatigue life prediction method based on plasticity induced crack closure is presented. Selecting the appropriate material plastic hardening model, and importing the shot peening residual stress as the initial stress by user subroutine SIGINI. The crack opening force was solved through the finite element model in each extending step, then the effective stress intensity factor was calculated and the fatigue life was predicted. By comparing the predicted results with the experimental results, the model and fatigue life prediction method were validated.(3) Based on the correct and effective model and research method, the crack closure effect and the fatigue life of shot peening and no shot peening were studied in several aspects, such as the smallest unit size at crack tip, stress ratio, initial crack length and shot peening process conditions. The general rule of effect factors and their incidence were analysed, so as to provide a beneficial role for practical engineering application.