Fracture behavior and numerical study of resistance spot welded joints in high strength steel sheet

Abstract

Cross tension tests of resistance spot welded joints with varying nugget diameter were carried out by using 980MPa high strength steel sheet of 1.6mm thickness. In proportion as nugget diameter increase from 3 t to 5 t (t; thickness) cross tension strength (CTS) increased, while fracture morphology simultaneously transferred from interface fracture to full plug fracture. In case of interface fracture, circumferential crack initiation due to separation of corona bond arose at early stage of loading. The crack opening process without propagation was recognized until just before fracture and then the crack propagated to nugget immediately in brittle manner around CTS. In full plug fracture, main ductile crack initiation from notch-like part at the end of sheet separation occurred with sub crack initiated at early stage. The ductile crack propagated toward HAZ and base material to form full plug fracture.