Analysis of hot cracking during lap joint laser welding processes using the melting state-based thermomechanical modeling approach

Although lap joint laser welding is in great demand in practice, very limited numerical studies have been performed to investigate the hot cracking behavior in this welding configuration. This is because the traditional numerical methods are ineffective in simulating lap joint welding processes, which requires consideration of the discontinuous thermomechanical fields across the metal sheet interface prior to joining and the complicated contact conditions that evolve with material phase transitions during the welding process. The aim of the present study is to introduce a new irreversible melting state variable into the thermomechanical coupled computational model to account for the melting state effects on the mechanical and thermal properties at the welding interfaces. Under this framework, the calculation of thermal conductance and frictional coefficient depends on both temperature and the melting state variable. This allows the proper thermal and mechanical contact conditions to be captured at various melting states during the whole welding process. The proposed melting state-based model has been applied to the simulation of lap joint laser welding for the numerical investigation of the critical crack initiation location as well as the influence of various processing parameters on the cracking susceptibility and the cracking mechanism during heating-cooling processes.