Failure analysis of dissimilar thickness resistance spot welded joints in dual-phase steels during tensile shear test

•This paper theoretically describes the failure modes and mechanism of RSW joints.•IF is mainly brittle fracture and PF is mainly plastic fracture.•The tensile stress leads to the IF and the shear stress leads to the PF.•The fracture is initiated from the DP780 sheet.

Investigating the failure mode and failure mechanism of the dissimilar thickness dual phase sheets resistance spot welding joints was the objective of this study. Three distinct failure modes were observed during the tensile shear test: interfacial, partial interfacial and pullout failure. The results of the stress analysis of welded joints show that the tensile stress leads to the interfacial failure and the shear stress leads to the pullout failure. Due to more serious stress concentration and heat affected zone (HAZ) softening of DP780 side, the fracture is initiated from the DP780 steel.