Failure behaviour of laser spot welds of TRIP800 steel sheets under coach–peel loading

Abstract

This study is carried out to investigate the laser spot welds (LSWs) of advanced high strength steel sheets of 1?0 mm thickness for application to the automotive industry. Mechanical properties and failure behaviour of LSWs for transformation induced plasticity steel sheets (TRIP800) subjected to monotonic coach–peel loading are investigated by experimental and finite element (FE) simulation methods. Microstucture of LSW and fracture surfaces of the welded specimens were examined by scanning electron microscopy (SEM) to describe the microstructural features and to clarify the crack initiation mechanism respectively. Based on simulation solutions equivalent plastic strain was obtained to describe local deformation of LSW joints. Experimental results revealed a ‘plug type’ of failure mode of the circular LSW joints under ‘peel–coach’ loading condition. This type of ductile failure is the most common failure mode for spot welds used in the automotive industry. Numerical simulation of damage process was compared with experimental results and this revealed that fracture path was successfully predicted.