Failure analysis of resistance spot welds in a DP1000 automotive steel: full field macro/ micro scale deformation analysis

The effect of welding parameters on local deformation and failure of resistance spot welds in a DP1000 high strength dual phase steel are investigated. A novel experimental framework is developed together with new sample geometries to investigate failure modes in the weld sections. Macro and microscopic experiments using optical and scanning electron imaging combined with digital image correlation are used to better understand the role of microstructural morphology and loading conditions on deformation and damage of the weld nugget in the studied materials. The results show a transition from the interfacial failure to pull-out failure as the welding current increases. The measured plastic strain at failure is larger for higher welding currents. The fracture surface at the nugget is dominated by brittle and shear fracture for interfacial failure mode in samples produced with lower welding current, however ductile and shear fracture are more pronounced on the samples with pull-out failure mode under higher welding current.