Evaluation of fatigue crack propagation in surface modification layer of duralumin treated by various peening

Abstract

Peening techniques are used to introduce the compressive residual stress into the surface of metallic materials in order to improve the fatigue properties. The fatigue crack propagation is affected by many factors in surface modification layer, however, the effect of these factors on the fatigue crack propagation is not clarified in detail. In this study, the fatigue crack propagation behavior in surface modification layer of duralumin treated by various peening techniques including shot peening, cavitation peening and laser peening was investigated. The relationship between the fatigue crack propagation behavior and mechanical properties was also evaluated. The fatigue crack propagation behavior varies depending on peening techniques despite the condition of the same peening intensity, since the mechanical properties in surface modification layer are changed with the peening techniques. The compressive residual stress σ_R and Vickers hardness HV are the important factors about fatigue crack propagation, however they do not show a correlation with the number of cycle to failure of the specimen N_f. Therefore, the new indicator combined with four factors i.e. σ_R, HV, full-width at half maximum β and maximum height roughness Rz were proposed. It revealed a significant correlation with N_f, and possibility to evaluate the effect of suppression of fatigue crack propagation by peening.