The failure modes of two single-weld specimens, the coach-peel and the tensile-shear specimens, were studied in detail. Weld overload experiments, along with optical and scanning electron microscopy, revealed that the coach-peel specimen failed by microvoid coalescence (ductile fracture) near the weld nugget/heat affected zone (HAZ) boundary and that the tensile-shear specimen failed predominately by localized necking (shear localization) near the HAZ/base metal boundary. Empirical data extracted from measurements performed on metallurgical cross sections of interrupted coach-peel and tensile-shear specimens established the deformed characteristic material distance (coach-peel) and the existence of a critical thickness strain for localized necking (tensile-shear). These quantities were used to predict weld failure via finite element analysis as described in Ref 1.
The work presented here is the first step in a larger project that is focused on developing a methodology for predicting spot weld overload failure in detailed finite element simulations of spot-welded joints. This methodology is based upon the failure phenomena (as reported here) and detailed characterization of the HAZ (as reported in Ref 1). The main requirement of this predictive methodology is that it be adaptable to any combination of joint configuration and loading direction. This predictive methodology will serve as the basis for the final step of developing a model of resistance spot weld failure based upon a simpler representation of the spot weld that can be used in car crash simulation models.