Bending fatigue behaviour of differently shot peened Al 6082 T5 alloy

The fatigue behaviour of the Al 6082 T5 alloy subjected to two different shot peening treatments was studied. The fatigue improvements with respect to the unpeened condition and the influence of the peening intensity on fatigue were discussed accounting for the effects of surface modifications (roughness and strain hardening) and of residual stresses. In particular, the extent of the residual stress redistribution during loading was investigated by means of X-ray diffraction (XRD) measurements. An evolution to a stabilised value of the surface stress, depending on the applied loads, was found. The initial and the stabilised residual stress profiles were considered for discussing the improvement in the fatigue behaviour due to peening. To this purpose, a multiaxial fatigue criterion was adopted to account for the biaxial residual stress field. Accordingly, an attempt to separate the effect of residual stresses from that of the microstructural modifications induced by the plastic deformation during peening was carried out and, in particular, the influence of the surface hardening was highlighted.