Local weld geometry-based characterization of fatigue strength in laser-MAG hybrid welded joints

This research studies the influence of local weld notch parameters on fatigue crack initiation sites in laser-hybrid butt welds, utilizing high-resolution 3D scans and fatigue tests to failure. The suitability of different local geometric weld notch parameters for fatigue strength characterization is investigated, and the current challenges associated with their measurements are highlighted. The weld notch shapes were found to fluctuate significantly, resulting in considerable variation in notch parameters over short intervals. Undercut depth was found to determine the critical location for crack initiation. There were several instances where the fatigue crack initiated from notches with large radii despite the presence of sharper notches, contrary to what is expected on the basis of previous investigations. The results of the present study indicate that the undercut depth is a suitable fatigue strength indicator for high-quality laser-MAG hybrid welds, overcoming the practical limitations of notch radius measurement.