Failure Mode of Laser Welds in Lap-Shear Specimens of HSLA Steel

Failure mode of laser welds in lap-shear specimens of high strength low alloy (HSLA) steel is investigated in this paper. The experimental results from quasi-static tests show that the laser welds failed in a ductile necking/shear failure mode near the heat affected zone. In order to understand the failure mode of these welds, a finite element analysis under plane strain conditions was conducted to identify the effects of the different plastic behaviors of the base metal, heat affected zone, and weld metal on the ductile failure. The results of the finite element analysis show that the higher effective stress-plastic strain curves of the weld metal and the heat affected zone results in the necking/shear failure mode. The deformed shape of the finite element model near the weld matches well with that of a failed weld. A finite element analysis of the lap-shear specimen with consideration of void nucleation and growth for all material elements based on the Gurson yield function was also carried out. The results of the finite element analysis based on the Gurson yield function are in good agreement with the experimental observations of the dimple fracture surface of the failed specimens.