Microstructure based modeling of deformation and failure of spot-welded advanced high strength steels sheets

Abstract

Microstructures and hardness of different weld zones of spot-welded high strength steel grade 1000 and press-hardened 22MnB5 steel were characterized. Tensile shear and cross tension test of welded specimens were conducted, in which load responses and fracture developments were identified. Then, samples with microstructures of each weld zone in all examined joints were generated by specific heat treatment processes. 2D representative volume elements (RVEs) for these microstructures were modelled. Flow stress curves of the individual phases were described by micromechanics based models under consideration of local chemical compositions and phase constituents. It was clearly shown that predicted overall stress-strain responses of all weld regions were well in accordance with the tensile test results of heat-treated samples. Furthermore, fracture criteria were determined for each weld zone by using samples having varying geometries for a wide range of stress triaxialities along with the digital image correlation technique. Finally, FE simulations of the tensile shear and cross tension tests of all investigated joints were carried out, in which the obtained flow stress curves and fracture criteria were defined for the individual weld regions. The experimental force-displacement curves up to fracture and observed failure occurrences could be correctly described by the simulation results.