3D modelling of plug failure in resistance spot welded shear-lab specimens (DP600-steel)

Ductile plug failure of resistance spot welded shear-lab specimens is studied by full 3D finite element analysis, using an elastic-viscoplastic constitutive relation that accounts for nucleation and growth of microvoids to coalescence (The Gurson model). Tensile properties and damage parameters are based on uni-axial tensile testing of the basis material, while the modelled tensile response of the shear-lab specimens is compared to experimental results for the case of a ductile failure near the heat affected zone (HAZ).

A parametric study for a range of weld diameters is carried out, which makes it possible to numerically relate the weld diameter to the tensile shear force (TSF) and the associated displacement, u (TSF) , respectively. Main focus in the paper is on modelling the localization of plastic flow and the corresponding damage development in the vicinity of the spot weld, near the HAZ.

For decreasing weld diameter, localization of plastic flow may be observed to occur in the weld nugget, introducing significant shearing. Due to these competing mechanisms a critical transition radius of the weld may be found. However, due to the limitation of the Gurson model in describing ductile failure at very low stress triaxiality, further analysis of the shear failure is omitted.