Eigenstrain modelling of residual stresses generated by laser shock peening

Abstract

This paper presents an eigenstrain (misfit strain) model of the residual stresses generated by laser shock peening (LSP). The shock wave is first modelled as a dynamic pressure load in an explicit finite element (FE) model and the stabilised plastic strain distribution is extracted. This strain distribution is then incorporated as an eigenstrain distribution in a static FE model and the residual stresses generated by the original shock wave are obtained as the elastic response to the eigenstrain. In order to focus on the basic mechanics, an elastic-perfectly plastic material model is assumed. Similarly, a simplified pressure/time variation (a triangular ramp with the peak pressure occurring at the half the total pulse duration) is assumed in order to characterise the pressure pulse. The peak pressure and the duration of the pressure pulse are determined in a way that they are consistent with experimental results. The analysis is extended to study the case of multiple pulses and the results show that the process generates compression in a surface layer of about 1.5–2mm deep. Furthermore, the results demonstrate that the magnitudes of subsurface tensile stresses are of the order of one fifth of the material's yield strength for typical peening conditions.