Abstract :
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, uT SF, 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.
