Determination of residual stresses in fibre laser welded AA2024-T3 T-joints by numerical simulation and neutron diffraction

摘要

This paper presents an experimental and numerical study of residual stress states and deformation in fillet welded AA2024-T3 T-joints produced using a high-power fibre laser. Welded sheets with one and three stiffeners were prepared, respectively, to determine changes in microstructure, residual stress, distortion and micro-hardness. 3D sequentially coupled thermo-mechanical finite element models were developed to analyse welding temperature fields, and accurately simulate welding residual stresses and deformation. The simulated results were calibrated using the experimental database on weld pool geometry obtained from optical metallography and temperature fields measured using thermocouples. Residual stress measurements were made using neutron diffraction techniques and sheet distortions were measured using a coordinate measuring machine. The influence of various mechanical boundary conditions on angular and cambering sheet distortions was examined to optimise the restraint parameters. The application of element death and rebirth and dummy element techniques were studied and compared to incorporate the effect of filler metal deposition during welding. The level of residual microstrain was evaluated by diffraction peak width analysis, which indicated the maximal values in the weld metal. The effect of grain growth with respect to strength was of minor importance, whereas, considerable softening in the weld metal was observed.