Prediction and characterization of plastic damage in a weld joint resulting from laser shock processing

In this paper the plastic damage in welded joint produced with gas tungsten arc welding (GTAW) induced by laser shock processing is investigated by finite element method (FEM). Plastic damage in the welded joint during laser shock processing (LSP) is modelled combined with Gurson-Tvergaard-Needleman (GTN) plastic damage constitutive equations. In order to verify the FEM model, benchmark simulations are performed and verified with available experimental results. Results show that predicted residual stresses agree well with the experimental data. A key point of interest is that welding tensile residual stress can be modified and changed into compressive residual stress due to laser shock processing. Plastic damage results reveal that void volume fraction (VVF) referring to ductile damage of materials is approximately constant and decays sharply at the edge of the processed region at the surface. The magnitude of surface VVF in the base metal and the welded joint all increase with increasing shock pressure, pressure pulse duration and shot number, however, it almost stays the same at the centre of the impact zone for different spot sizes. A point should be noted that surface VVF in the welded joint is slightly larger than that in the base metal.