Vibration fatigue analysis for multi-point spot-welded joints based on frequency response changes due to fatigue damage accumulation

► We estimated S–N curve of a spot-welded joint using fatigue test and a FE analysis. ► We analyzed the change in frequency response as damaged welding point increase. ► Fatigue life was computed by combining transfer functions, S–N curve and input PSD. This study conducted a vibration fatigue analysis that considered changes in frequency response resulting from the cumulative fatigue damage to multi-point spot-welded joints in an automotive body. The S–N curve was obtained using a fatigue test for tensile-shear spot-welded (single-point) joint under constant amplitude load and a finite element analysis based on the Rupp/LBF model. In addition, a vibration fatigue analysis that considered changes in the frequency response due to the fatigue damage was conducted on multi-point spot-welded joints. The fatigue life of the spot-welded joints was computed by combining the transfer function, the S–N curve of the tensile-shear spot-welded joint and the input PSD. Furthermore, a vibration fatigue test using an electronic dynamic shaker was conducted to verify the results of the analysis. The fatigue life by the proposed method was in conformance with the test results.