Failure Mechanism of Laser Welds in Lap-Shear Specimens of a High Strength Low Alloy Steel

In this study, the failure mechanism of laser welds in lap-shear specimens of a high strength low alloy (HSLA) steel under quasi-static loading conditions is examined based on the experimental and computational results. Optical micrographs of the welds in the specimens before tests were examined to understand the microstructure near the weld. A micrographic analysis of the failed welds in lap-shear specimens indicates a ductile necking/shear failure mechanism near the heat affected zone. Micro-hardness tests were conducted to provide an assessment of the mechanical properties of the joint area which has varying microstructure due to the welding process. A finite element analysis was also carried out to identify the effects of the weld geometry and different mechanical properties of the weld and heat affected zones on the failure mechanism. The results of the finite element analysis show that the geometry of the weld protrusion and the higher effective stress–plastic strain curves of the heat affected and weld zones result in the necking/shear failure of the load carrying sheet. The deformed shape of the finite element model near the weld matches well with that near a failed weld. A finite element analysis based on the Gurson yield function with consideration of void nucleation and growth was also carried out. The results of the finite element analysis indicate that the location of the material elements with the maximum void volume fraction matches well with that of the initiation of ductile fracture as observed in the experiments.