Three-dimensional modelling of coupled flow dynamics, heat transfer and residual stress generation in arc welding processes using the mesh-free SPH method

Abstract

In this paper, a novel mesh-free approach is applied for modelling thermo-mechanical responses in a three-dimensional arc welding configuration using the Smoothed Particle Hydrodynamics (SPH) method. A fully coupled three-dimensional elastoplastic and heat transfer analysis is used to study the flow pattern of the filler material, and the resulting plastic strain development and temperature distributions for a simple arc welding configuration. The mesh-less and Lagrangian nature of SPH enables modelling of problems with large deformation and discontinuities, avoiding several disadvantages of the traditional mesh-based methods (e.g., FEM, FDM and FVM), and it is also able to implement coupled physics and complex constitutive behaviours due to the history tracking ability of the method.The plastic deformation and temperature distribution of the metal in the weld pool and the surrounding parent material are analysed during the cooling stage using SPH, and the resulting residual stresses are evaluated. This work establishes the capability of SPH as a three-dimensional modelling tool for gaining insights into the key physical processes of material deposition and its subsequent evolution during welding processes. Arc welding generates a non-uniform plastic strain distribution. The welding speed is found to be a crucial factor in controlling the plastic strain distribution and the quality of the welded joint, and there is a critical welding speed which produces the most uniform plastic strain distribution in the weld pool.The SPH method is able to predict the long term thermo-mechanical responses, namely heat transfer and residual stresses in the welded joint during the cooling stage. The SPH solutions demonstrate non-uniform cooling rates and temperature fields in a workpiece, as exhibited in practical welding processes. The solutions also show the existence of high temperature gradients around the boundary of the weld, which causes rapid microstructural and phase transformations. The SPH method also incorporated the evaluation of thermal residual stresses in the workpiece. In the early stages of welding, the residual stress varies rapidly with time and subsequently changes gradually. The residual stress variation over the welded joint depends on the local temperature gradients. The residual stress is very high at the interface between the filler and parent material and decreases rapidly further away from it. The typical thermo-mechanical behaviour found in the present study conforms to the observations of real life arc welding processes.