Design optimization of spot-welded plates for maximum fatigue life

Resistance spot welding is the most preferred and widely used method for joining metal sheets in automotive and many other industrial assembly operations. Spot-welded joints are usually the weakest parts of structures leading to fatigue failure under fluctuating loads. Increasing the fatigue strength of the joints through geometrical changes will also increase the overall integrity of the whole structure.In this study, a methodology is proposed to find the optimum locations of spot welds and the optimum overlapping length of the joined plates for maximum fatigue life. Minimum weld-to-weld and weld-to-edge distances recommended by the industry are considered as side constraints. The total strain life equation is used to predict the fatigue life. In order to use this model, the strain state in the structure developed under cyclic loading is required. For this purpose, a nonlinear finite element analysis is carried out, taking into account residual stresses due to localized plastic deformations around the spots. Nelder-Mead (Sequential Simplex) is employed as the search algorithm in the optimization procedure. A number of problems are solved to demonstrate the effectiveness of the proposed method.