Characterisation of actual weld geometry and stress concentration of butt welds exhibiting local undercuts

Nowadays automated welding processes produce high-quality welds with smooth and regular global weld geometry. However, the local geometry of the weld exhibits a certain amount of variance in its topography due to dynamic effects of the welding process itself. The subsequent change in local stress concentrations affects the fatigue behaviour of welded structures. In literature, numerous equations for the estimation of a weld's stress concentration based on characteristic parameters of the weld geometry are available. Three-dimensional scans of ultra high-strength steel butt welds exhibiting local undercuts are processed with digital image acquisition to derive weld geometry parameters, which facilitate a subsequent statistical analysis. Hereby, a novel approach to estimate the local weld toe radius is presented. Furthermore, the derived values are utilized to calculate the respective stress concentration at various locations of the weld using state-of-the-art notch-factor approximation equations. For undercut-free samples, a comparison of the investigated notch stress concentration equations and the results of numerical simulations of the actual weld geometry show good accordance for all models. However, at locations with a distinct undercut, the stress concentration is consequentially underestimated. Therefore, an improved approach extending the existing notch-factor equations is presented. It enables the consideration of the stress concentrating effect of a local undercut at the weld toe.

Automated summary

Automated welding processes produce high-quality welds with smooth and regular global geometry, but the local geometry variations due to dynamic effects impact fatigue behavior; Estimation of stress concentration in welds based on characteristic parameters is common, but underestimation occurs at locations with distinct undercuts; An improved approach is presented to consider the stress concentrating effect of local undercuts at the weld toe.