Application of Weld Fatigue Evaluation Procedure for Considering Multi-Axial Stress States Using the Battelle Structural Stress Method

Even under uniaxial loading, seemingly simple welded joint types can develop multi-axial stress states, which must be considered when evaluating both the fatigue strength and failure location. Based on the investigation of fatigue behavior for the multi-axial stress state, a procedure for fatigue behavior of welded joints with multi-axial stress states was proposed using an effective equivalent structural stress range parameter combined normal and in-plane shear equivalent structural stress ranges and the master S-N curve approach. In automotive structures, fatigue failure is often observed at weld end, which often show a complex stress state. Due to simplified weld end representation having a sharp right-angled weld corner, the fatigue failure prediction at the weld end tends to be overly conservative due to the excessive stress concentration at the right-angled weld termination. In order to overcome this modeling limitation, an extended weld-end correction procedure considering the stress behavior of the element adjacent to the weld end and reducing the mesh sensitivity in this region, was proposed. When the extended weld-end correction procedure and the effective equivalent structural stress range parameter was applied to the failure at the weld end, the fatigue predictions are improved. Therefore, the procedure using the effective equivalent structural stress range parameter can be generally applicable to predict the failure location and the fatigue life at welds of interest.