Fatigue life analysis in the residual stress field due to resistance spot welding process considering different sheet thicknesses and dissimilar electrode geometries

A typical vehicle body contains many 3-sheet spot-welded connections with different sheet thicknesses. In addition, the use of dissimilar electrode geometries is extremely common in the automotive industry. These two factors lead to an asymmetric spot weld with asymmetric residual stress distribution and heat-affected zone. This asymmetry has considerable effects on the fatigue behavior of these joints. Although many previous studies were dedicated to the analysis of spot welds, consideration of different electrode geometries and fatigue analysis of 3-sheet spot-welded joints are absent in the literature. To this end, in the present paper, the resistance spot weld process of three-sheet low carbon steels considering different sheet thicknesses and dissimilar electrode geometries (F0 and D0) was simulated. The finite element simulation presented, was verified by comparison to the experimental results for the nugget size and residual stress. Residual stress distribution diagrams were obtained with respect to the distance from the center of the nugget in four different paths. Eventually, fatigue life analysis of this type of joint was performed using the finite element method. The results indicate that the finite element-based fatigue results are within the scatter band of the experimental results (75/75 tolerance limits), and consequently, the provided algorithm can be reliably used to analyze the fatigue behavior of spot-welded connections with complex specifications.