Fatigue Life Prediction in Spot Welded Rectangular Section Members under Springback Effect

Abstract

Most automobile body members are fabricated from formed steel sheets joined by spot welding, and these welded joints typically tend to cause fatigue failure owing to local stress concentrations. In this study, fatigue tests were conducted under cyclic torsion loads using spot-welded rectangular section members made of 590 MPa grade dual-phase high-strength steel to investigate the springback effect on fatigue properties. These members were assembled using the rectangular sections that were formed under different blank holder forces, as this would change the amount of springback. Furthermore, the prediction of the fatigue life of these members was attempted through springback analysis, an elastic analysis together with a method of fatigue life prediction for spot welds using nominal structural stress. In this prediction, residual stress caused by springback was regarded as the mean stress. Concerning the experimental results, every fatigue failure was initiated close to the spot weld edge located at the center of the tested members, and fatigue life decreased with springback amount increasing. In addition, the predicted results were generally in agreement with the experimental results in terms of the effect of springback.