Residual stress near single shot peening impingements determined by nanoindentation and numerical simulations

The near-surface hardness and residual stresses resulting from a single shot peening impingement on aluminum alloy 2024-T351 were assessed by nanoindentation with spatial mapping of mechanical properties on cross sections through an impingement. For residual stress, a procedure was developed to couple nanoindentation experiments with numerical simulations for better understanding and predicting the effects of shot peening. A surface preparation method was developed that exposes the cross section of a single shot impingement for nanoindentation tests, while at the same time obtaining accurate measurements of the impingement dimensions. Starting parameters for the numerical simulation in terms of shot diameter and the shot velocity were selected to best match measurements of the impingement depth and diameter. The experimental results indicated that the greatest hardness was located at the nearest indent to the peened surface, whereas the maximum compressive residual stress was located sub-surface. When comparing experimental and numerical residual stresses, the experimental results showed a greater maximum compressive residual stress that was in closer proximity to the peened surface. Overall, residual stress fields compared between experimental and numerical results were similar, and differences could be explained in terms of the effect of strain hardening. The current work demonstrated the usefulness of coupling nanoindentation experiments with numerical simulations for evaluating the surface modifications resulting from a single shot peening impingement.