Study on the thermal and residual stress by welding and laser surface hardening using a new two-dimensional finite element model

The transient thermal stress and residual stress in bead-on-plate welding and laser surface hardening was analysed by employing a new two-dimensional finite element model. In the formulation, the sliced solution domain possessing one element in the welding or hardening direction was introduced to allow the change of longitudinal total strain along the width and depth of the specimen. The longitudinal total strain, which makes the resultant force in the longitudinal direction zero, was used as the boundary condition. To determine the longitudinal total strain, the equations of the compatibility, force equilibrium and moment equilibrium were considered. Calculation of the transient temperature distribution was based on the two-dimensional finite element model of the quasi-stationary condition. By using the proposed model the thermal and residual stresses of the bead-on-plate welding and laser surface heat treatment were successively calculated. Especially in laser surface hardening, the thermal stress was induced mainly from the temperature gradient and martensitic phase transformation, which was found to have a greater influence on the residual stress than the former. The computed results were compared with those obtained by the conventional two-dimensional model of the plane strain condition. The simulation results revealed that the present model could more reasonably describe the thermal and residual stresses than the plane strain model.