Joint strength and failure mechanism of laser spot weld of mild steel sheets under lap shear loading

Abstract

Ultimate strength and failure mechanism of laser spot welds under lap shear loading were investigated. Optical micrographs of cross-section of spot welds before and after failure were examined to understand the failure behaviour. The experimental results indicate that laser spot welds can fail in two distinct modes, namely interfacial and pullout failure. A failure mechanism which was confirmed by SEM investigations was proposed to describe these two failure modes. According to the experimental observations, a simple stress solution related to the far field load was conducted and the critical weld nugget diameter to ensure pullout failure mode was estimated. The results were compared with the experimental data and also with the test data of resistance spot welds. It was observed that the critical nugget diameter of laser spot welding was larger than that of resistance spot welding due to the different failure location in pullout mode. Furthermore, the effect of welding parameters on joint strength and failure mode was studied.