Relaxation of Peening Residual Stresses Due to Cyclic Thermo-Mechanical Overload

Shot-peening induced residual stresses can be relaxed due to cyclic loading. This relaxation plays an important role in determining the fatigue life of the peened components. It is therefore the purpose of this study to conduct comprehensive three-dimensional dynamic elasto-plastic finite element analysis of the joint peening treatment and relaxation process. In this regard, a novel symmetry cell is developed and used to model the multiple impact indentations resulting from multiple impingements of a cluster of shots. The model was further extended to integrate the relaxation resulting from cyclic loading at stresses above the yield strength of the material. This integrated model accounts for the main features of both stages by considering strain-rate effects, shot and target inertia and the dependence of the mechanical properties of the target material on temperature. A wide spectra of cyclic mechanical and thermal loads as well as their combinations is considered and the resulting relaxed residual stress field is determined. As an application, the model was used to predict the residual stress relaxation in a high-strength steel target made from AISI 4340 under different peening and thermomechanical cyclic overload.