Analysis on fatigue characteristics of spot welded joints of stainless steel car body

In order to obtain the fatigue characteristics of the spot welded structure of the stainless steel car body, the S-N curve and P-S-N curve for fatigue life assessment of spot welding were proposed. Firstly, the tensile-shear fatigue tests were performed to obtain the fatigue life of the spot welded samples. Then, the finite element models of the spot welded samples were established by solid elements and shell elements respectively. The simulation results were compared with the quasi-static test results to verify the accuracy of the finite element model established by shell elements. Then, the equivalent structural stress values of the spot welded samples were obtained based on the Rupp method. The S-N curves of the spot welded samples at different stress ratios were obtained according to the equivalent structural stress and the test life. In order to eliminate the effect of the stress ratios on the S-N curves, the structural stress under the asymmetric cycle was equivalent to the structural stress under the symmetrical cycle based on the Goodman correction method. Thus the basic S-N curve of the spot welded samples was obtained. Finally, the P-S-N curves of spot welding were drawn based on three methods. By comparing P-S-N curves, method 1 based on failure rate and method 3 based on equivalent life can accurately predict the real life of spot welding, which provides some reference for the design and life prediction of spot welded structures.