Surface layer modifications of micro-shot-peened Al-7075-T651: Experiments and stochastic numerical simulations

Shot peening is widely used to improve the fatigue resistance of metallic components, but the optimal tuning of the treatment parameters is not an easy task. Finite element (FE) dynamic simulations proved to be a reliable tool to estimate the effect of the main treatment parameters on surface roughness and residual stresses. This paper presents one of the first attempts to numerically simulate a micro-shot peening treatment; indeed, this is a tre- mendous numerical challenge given the large number of impacts to be simulated and the fine mesh needed to discretize the small impact dimples. The target material is the aeronautical aluminium grade Al-7075-T651. To best represent the hardening rule of the target material, the Lemaitre-Chaboche model is tuned on the basis of fully reverse axial strain tests. The statistical nature of the peening treatment is taken into account by randomly generating sets of bead individuals characterized by stochastic variability in dimension, velocity and impact loca- tion. Surface roughness and residual stresses resulting from the numerical analyses are compared with experi- mental measurements. A specific novel procedure is proposed to take into account the effect of surface roughness and radiation penetration on the in-depth residual stress profile measured by XRD. In addition, a static finite element model is devised to estimate the concentration effect exerted by the surface roughness on the ex- ternal stress field.