Analytical and Experimental Investigation of the Effects of Spot Weld Diameter, Gap Distance and Electrode Force on the Mixed Mode of Resistance Spot Welded-Joints

The effects of mixed mode fracture and fatigue crack path have been investigated in tensile-shear spot weld specimens having different gaps between their sheets. Non-linear analysis has been performed to obtain the stress distributions along the line perpendicular to the fatigue crack path. The amounts of effective stress and notch strength reduction factors have been obtained using the volumetric method. Fatigue crack growth approach has been applied to obtain stress intensity factors in mode I and mode II of fracture and to estimate fatigue crack propagation of spot welds. The results obtained from numerical predictions such as the volumetric method and the fatigue crack growth approach have been compared with the available fatigue test data. The results obtained from the fatigue crack growth approach show that spot weld specimens with bigger nugget diameter have the smaller values of stress intensity factors compared with those spot welds with smaller nugget diameters. However, with due attention to the fact that fatigue cracks propagate in the mixed mode condition, the ratio of mode I stress intensity factor to the mode II become more important parameter while predicting the fatigue life of specimens.