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
Welding generates a considerable amount of residual stresses which affect the structural integrity of welded components. It is often assumed that the magnitude of residual stresses around the welded joint is as high as the yield stress of the material. In this investigation, such assumption was found to be overly conservative and failed to accurately represent the distribution of residual stresses in fibre laser welded aluminium alloy 2024-T3 sheets. Welding simulation based on the finite element method was used to reliably determine the distribution and magnitude of transient residual stress fields and distortions in thin sheets welded using three different sets of welding parameters. The accuracy of the finite element models was checked by calibrating with experimentally measured weld pool geometries and temperature field prior to conducting parametric studies. X-ray and neutron diffraction measurements were performed on the surface and in the bulk of the welded components, respectively and compared with numerical results. The influence of weld metal softening, welding parameters and restraints on residual stresses and distortion were investigated systematically by numerically simulating ideal conditions which eliminate the practical limitations of conducting experimental studies, for process optimization as well as evaluation of in-service structure integrity and failure modes of the welded sheets.
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