Damage behavior and fatigue life prediction of plug-welded joints in vehicle bodies made of weathering steel

To investigate the fatigue performance of weathering steel plug-welded joints, fatigue tests were conducted on three types of single-point plug-welded specimens under different load levels. The fracture characteristics were analyzed, and a CWELD nugget finite element model of the plug-welded specimens was established. Based on the coarse mesh hybrid structural stress method, the S s -N (structural stress-life) curves of the plug-welded specimens were obtained, and the effects of load ratio, opening plate thickness, and hole diameter on their fatigue performance were examined. Finally, the S s -N curves were corrected using the quasi-Newton method, and the fatigue damage of plug welds in the weathering steel car body was calculated. The results show that the influence of load ratio on the S s -N curves is negligible. Increasing the hole diameter significantly improved the joint fatigue life, reaching 3.34 times that of the original at a cyclic load level of 3.56 kN. Reducing the plate thickness slightly increased the fatigue life, with an improvement of approximately 10% in the high-stress region. Applying the corrected S s -N curve to calculate the plug weld life of the car body indicated that, under cumulative damage from three-directional acceleration conditions, all plug welds met the standard requirements, thereby satisfying the design criteria for the car body.