Comparative evaluation of plane-bending fatigue behavior of resistance spot-welded joints in dual-phase steels of different strength levels

This study attempted to explain comparatively the plane-bending fatigue behaviors of resistance spot-welded junctions using commercial DP600 and DP1000 automotive steel sheets having different strength levels.In addition, the fracture modes of the samples were evaluated and interpreted according to SEM examinations.First, standard junction samples were produced via resistance spot welding using two weld currents and three different electrode pressures.Microimage analysis and plane-bending fatigue tests were carried out on the samples.The maximum strain energy hypothesis was applied experimentally to obtain the fatigue test load force, and plane-bending fatigue stress values were obtained.Unlike the load/cycle graphics generally presented in the literature, Wohler S-N graphics were drawn, making this study different from others.The results of this study demonstrated that an increase in welding current led to an increment in fatigue strength.A significant relationship was also observed between weld nugget attributes and fatigue strength.Moreover, some intriguing results were obtained, e.g., the low-cycle fatigue life of the DP600 samples exhibited lower fatigue strength than that of the DP1000 samples; however, the high-cycle fatigue life of the DP600 samples showed higher fatigue strength than that of the DP1000 samples.