Modeling of deformation and failure behavior of dissimilar resistance spot welded joints under shear, axial and combined loading conditions

This paper presents the modeling of deformation and failure behavior of dissimilar resistance spot welded joints (RSW) between hot-stamped ultra-high strength (22MnB5) and microalloyed (HC340LAD) steels. For the determination of the deformation and the failure behavior of the different material zones of the weld, tensile and shear tests, that were cut from the base metals, the weld nugget and heat treated sheets were tested and modeled using the Gologanu-Leblond model coupled with the fracture criteria of Thomason and Embury. The joints were modeled using detailed 3-dimensional finite element models taking into account the different weld zones, i.e. base metal (BM), heat affected zones (HAZ) and weld metal (WM), their dimensions and their mechanical properties. Simulations of the spot welded joints' behavior under shear, axial and combined axial and shear loading were carried out and compared to experimental results such as force-displacement curves, load bearing capacity, fracture mode and fracture location. Maximum loads and force-displacement curves from experiments and simulations showed good agreements for all loading situations examined. Despite of its superior strength, pull-out fracture of the joints took place in the coarse grain HAZ of the hot stamped ultra-high strength steel in experiments and simulations.