Numerical prediction of plastic deformation and residual stresses induced by laser shock processing

Laser shock processing (LSP) involves a high-energy laser beam combined with suitable overlays to generate high pressure pulses on the surface of the metal. This stress wave propagates into the material, causing the surface layer to yield and plastically deform, and thereby, develop a significant residual compressive stress in the surface of the metallic material. This compressive stress field is beneficial for surface mechanical properties such as fatigue, wear or corrosion. After briefly reviewing the mechanism of shock wave formation, a numerical algorithm to predict this stress field is presented. To calculate the surface compressive stress, several experimental and analytical formulations with simplified assumptions have been reported in the literature. The proposed method uses a finite difference algorithm to simulate propagation of stress wave in the material. This module is explicitly coupled at each time step with a finite element module to predict deformation and stresses. The proposed method is implemented in a computer code and several problems are tested. The comparison of the calculations using the proposed numerical model with experimental results as well as with results obtained by analytical solutions shows a very good correlation.