Effect of hammer peening on fatigue life of aluminum alloy 2A12-T4

In this study, a series of tests were conducted in aluminum alloy 2A12-T4 to investigate the effect of hammer peening process on the fatigue behavior of holes in specimens. The fracture surfaces of the specimens were observed by means of an optical microscope in order to disclose the mechanism of fatigue failure. The finite element method (FEM) was used to analyze the distribution of residual stress around the holes which were preliminarily treated with hammer peening. The results revealed that the crack of a hammer peened hole always initiated at the peened face. The fatigue life of these hammer peened holes significantly was prolonged five fold compared to non-hammer peened holes. Their fatigue life showed a positive correlation with the residual plastic strain which was induced by hammer peening process. The longest fatigue life was found in cases in which the residual plastic strain surrounded the whole bore of the hole but did not emerge at the fix face.