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In this paper, the fatigue behavior of laser welds in lap-shear specimens of non-galvanized SAE J2340 300Y high strength low alloy (HSLA) steel sheets is investigated based on experimental observations and a fatigue life estimation model. Optical micrographs of the laser welds before and after failure under quasi static and cyclic loading conditions are examined. The micrographs show that the failure modes of laser welds under quasi-static and cyclic loading conditions are quite different. Under quasi-static loading conditions, the weld failure appears to be initiated from the base metal near the boundary of the base metal and the heat affected zone at a distance to the pre-existing crack tip, and the specimens fail due to the necking/shear of the lower left load carrying sheets.

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.