Geometrical Aspects of the Fatigue Behaviour Of

Cracking of laser hybrid welding of eccentric fillet joints has been studied for stainless steel. Laser hybrid welding enables narrow deep welds with freedom for shaping the upper weld geometry. The significance of geometrical aspects like weld toe radius, weld surface topography and lack of fusion on fatigue cracking is discussed. Constant amplitude four point bending tests, S/N-curve, topography measurement, microscopic analysis, finite element analysis (FEA) and other methods were carried out. Cracking is initiated inside the weld, thus not in the HAZ. The influence of both global and local weld geometry, like the toe radii, on the stress concentration factor was studied by FEA. The FEA revealed that surface roughness profiles can generate high stress peaks. In particular, it was found that the typical fishbone-like resolidification pattern at the top surface determines the crack propagation direction at the surface. Thus not necessarily the toe radius but rather the surface topography determined the crack initiation. Correlations between toe radii, the corresponding stress maxima and FAT values of each specimen were studied. Moreover, it could be explained why even significant lack of fusion does not affect stress raisers during the initial cracking phase, as long as the lack of fusion interface experiences compressive stresses only.