Failure modes of gas metal arc welds in lap-shear specimens of high strength low alloy (HSLA) steel

The failure modes of gas metal arc welds in single lap-shear specimens of high strength low alloy (HSLA) steel are investigated in this paper. Notched lap-shear specimens of gas metal arc welds were made. Quasi-static test results showed two failure locations for the welds. The specimens cut from coupons with shorter weld lengths failed near the weld root whereas the specimens cut from coupons with longer weld lengths failed near the weld toe. Scanning electron and optical microscope images of the failure surfaces and cross sections showed that the gas metal arc welds failed in a ductile necking/shear failure mode. Micro-hardness tests were conducted to provide an assessment of the mechanical properties of the base metal, the heat affected zone, and the weld metal. In order to understand the failure modes of these welds, finite element models were developed with the geometric characteristics of the heat affected zones designed to match the micrographs of the cross sections for the long and short welds. Three-dimensional finite element analyses were conducted with consideration of micro void nucleation and growth. The distributions of the void volume fraction near the welds shown from the finite element analyses are consistent with the failure modes observed in the experiments. Further finite element analyses were conducted in order to understand the effects of the geometric characteristics of the heat affected zone. The results showed that the geometric characteristics of the heat affected zone have a negligible effect on the load-displacement results; however, the geometric characteristics of the heat affected zone are key factors for the resulting failure location. Finally, finite element analyses were conducted in order to understand the effects of the weld metal geometry. The results indicate that the weld penetration and the weld toe angle have negligible effects on the load-displacement response, the peak load, and the predicted failure locations.