The critical role of fretting wear in the analysis of fretting fatigue

A finite element based approach is used to predict the effect of fretting wear on fretting fatigue life in the commonly used ‘rounded edge punch on flat’ laboratory geometry. The method predicts and hence explains experimentally observed phenomena, such as cracking location under the contact and dependence of fretting fatigue life on slip amplitude, which were not previously predictable. The results from the model are compared against available test data across a range of slip amplitudes. The model predicts a significant effect of slip amplitude on fretting fatigue life and, in particular, the well-known phenomenon of a critical range of slip amplitude for minimum life. The sensitivity of life and cracking location to the assumed value of wear coefficient on life and cracking location is studied for a partial slip case and it is shown (i) that the location of cracking switches from the contact edge to the stick–slip interface with increasing wear coefficient and (ii) that there is an associated critical value of wear coefficient which gives a maximum fretting fatigue life. For gross sliding cases, failure is always predicted at the contact edge. The work shows that inclusion of the effects of wear on fatigue damage accumulation is necessary for prediction of fretting fatigue life and cracking location.