Effects of Surface-level Defects on Tensile and Fatigue Strength of Spot Weld Bonding – Three-sheet Steel

The Resistance Spot Welding (RSW) technique is a prevalent method for joining thin metal sheets, particularly in transportation-related industries such as automotive and aerospace. A key advantage of RSW lies in its efficiency and the absence of additional materials, which contribute to structural weight reduction. In this study, the influence of visible defects (i.e., edge and intersection) on the mechanical behavior of triple-layer welded joints under static and fatigue loads is analyzed. To this end, a combination of laboratory testing and Finite Element Modeling (FEM) was utilized. The FEM approach was validated using experimental axial fatigue data (high-cycle S-N curves). Unlike prior research, this investigation incorporates such as surface-level defects into the FEM framework for the first time. Simulation results showed that a 0.2 mm edge defect leads to tensile and fatigue strength decrease of 5.4 % and 13.72 %, respectively, while a 0.6 mm intersection defect for the static and fatigue strengths causes reduction of 9.6 % and 54 %, respectively. These findings highlight the fatigue strength’s higher sensitivity to such defects compared to tensile strength.