| Components which are subjected to cyclic load often cause crack on account of local damage and under certain conditions, the crack will continue to propagate resulting the components completely failure eventually. In engineering practice, most failure of the components is caused by fatigue fracture and more than 80% of the crack initiate from the surface of the components in the failure. For fatigue failures, many process methods are adopted to improve the surface properties and suppress the initiation and propagation of the fatigue crack and improve the fatigue life and reliability of the components. Shot-peening is one of the most popular surface hardening technology domestic and aboard, which enables the surface occur plastic deformation by the impact of the shot, changing the surface morphology and stress distribution, influencing the fatigue life of components. Now, the research of shot-peening on fatigue life focused on the positive effect of residual stress field, and the study of the negative effect of the surface morphology is few. In this paper, a shot-peening numerical simulation model is established using ABAQUS software. On the one hand, the effect of surface topography on fatigue crack initiation life is studied and on the other hand, the influence rule of residual stress on fatigue crack closure effect and its effect on fatigue crack propagation life is analyzed. The main research contents are as follows:(1) Firstly, a shot-peening finite element model is established by the ABAQUS/Explicit software and is verified by comparing the residual stress numerical results with the experimental results. Then, the influence of different shot-peening process parameters on surface roughness is analyzed through the orthogonal test. On the basis of it, the effect of it on the stress concentration factor and fatigue crack initiation life is studied.(2) The critical factor of shot-peening improve the fatigue life is the residual compressive stress enhance the crack closure effect. A fatigue life prediction analysis method of residual stress field is proposed based on crack closure theory. The finite element model is established according to the experimental conditions and introducing the initial residual stress field by user subroutine SIGINI. The crack opening force is solved by analyzing the crack contact state, then calculating the crack closure factor and the fatigue crack propagation rate, predicting fatigue propagation life. Subsequently, based on the above model, the influence rule of the residual stress, stress ratio and element size at the crack tip on the crack closure effects is analyzed, so as to deepen the understanding of the mechanism of shot-peening residual stress on fatigue life.(3) Using the numerical solution of crack opening force to predict the fatigue life method, crack propagate along the predefined I path, it has strict requirements for the crack tip element size. To avoid the above shortcomings, an extended finite element method (XFEM) combined with a virtual crack closure technique (VCCT) is adopted to form a new method of prediction of the fatigue life. Virtual crack closure technique is used to calculate the crack tip energy release rate, combining the direct cycle method with the low-cycle fatigue fracture criterion to obtain stability response under cyclic load, quantitatively analyzing the fatigue life under the presence of residual stress. |
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