On the effect of shot-peening on fretting fatigue of Al7075-T6 under cyclic normal contact loading

In this investigation, the effect of shot-peening on fretting fatigue life of Al7075-T6 under cyclic normal contact loading is investigated experimentally using a new testing apparatus. A Finite Element model was developed to study the influence of shot-peening on crack propagation lifetime. The crack initiation life was calculated by a combination of numerical and experimental results. It was found that, while cyclic contact loading diminishes the fretting fatigue life significantly, shot-peening can enhance it remarkably. Depending on stress level, introducing residual compressive stresses led to an improvement of about 16-110% and 44-162% in crack propagation and crack initiation lives, respectively. Optical microscopy examination of fretting scar revealed that shot-peened specimens have wider slip area in contact interface due to the higher reaction surface and subsequently higher oxidation rate, particularly for cyclic contact loading in which the contact load is released in each cycle and the fretted interface is exposed to air for longer duration. The predicted crack growth lives agreed with the experimental results.