Residual stress measurement on shot peened samples using FIB-DIC

Shot peening is an established technique for improving the fatigue resistance of mechanical components by performing a deformation treatment that causes local near surface plastic deformation and introduces a layer of compressive residual stress. The knowledge of the residual stress distribution plays a crucial role in the correct prediction of fatigue life during service in the context of engineering design. Reliable prediction of safe fatigue life requires knowing how the residual stress state obtained after shot peening depends on the sample geometry, e.g. the presence of notches, and how it evolves during cyclic loading. The Focused Ion Beam milling coupled with Digital Image Correlation (DIC) analysis of SEM images (the FIB-DIC method) has been shown to be an efficient technique for stress evaluation at the (sub)micron-scale. The residual stresses in the vicinity of shot-peened rounded notch tips in Al-7075-T651 samples were studied as a function of notch radii (ρ = 2, 0.5, 0.15 mm). The interpretation of the results is aided by comparison with a simple numerical model of eigenstrain cylinder.