Modelling of the Mechanical Response in 304 Austenitic Steel during Laser Shock Peening and Conventional Shot Peening

Laser Shock Peening (LSP) and conventional Shot Peening (SP) are processes that aim to improve the surface properties of a workpiece by inducing compressive residual stresses. The peening processes also cause martensitic phase transformation in austenitic steels. Interestingly, experimental studies report significant differences in martensite content depending on the used peening process. This study aims to present numerical simulations of both peening processes. The study is based on a constitutive model which considers rate-dependent elasto-viscoplastic behaviour allowing for martensitic transformation. The results show the influence of spot size, laser pulse duration and laser intensity on the mechanical response. The differences in martensite content are investigated in terms of the corresponding transformation and yield surface evolution. The main finding of the study is an explanation for the significantly higher amount of martensite that is found after SP in comparison to LSP. It has been found that the main reason is not the intensity, but the stress trajectory in the stress space, which is inherently different between the two processes.