Transition in Interfacial Failure Mechanism of Resistance Spot Welds during Tensile–Shear Loading: Role of Fusion Zone Hardness

The failure of resistance spot welds through the fusion zone along sheet/sheet interface (i.e., interfacial failure) is critical for automotive crashworthiness. This paper investigates effect hardness on behavior during tensile–shear test. AISI 1040 medium carbon steel, producing a high level mismatch welding, was selected as base metal. By ex situ tempering heat treatment, various levels are achieved in with constant size. It shown that competition between ductile shear and rapid crack propagation. found there beyond which mechanism transitions from to In hardness, growth, fracture toughness governing factor load. Conversely, low FZ failure, would be