Search Results

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.

Lightweight, optimized vehicle designs are paramount in helping the automotive industry meet reduced emissions standards. Self-piercing rivets are a promising new technology that may play a role in optimizing vehicle designs, due to their superior fatigue resistance compared with spot welds and ability to join dissimilar materials. This paper presents a procedure for applying the mesh-insensitive Battelle Structural Stress Method to self-piercing riveted joints for fatigue life prediction. Additionally, this paper also examines the development of an interim fatigue design master S-N curve for self-piercing rivets. The interim fatigue design master S-N curve accounts for factors such as various combinations of similar and dissimilar metal sheets, various sheet thicknesses, stacking sequence, and load ratios. A large amount of published data was collapsed into a single interim S-N curve with reasonable data scattering.

Welding induced residual stresses are an important factor to consider when evaluating fatigue design of welded automotive parts. Fortunately, design engineers have various residual stress mitigation technologies at their disposal for improving the fatigue performance of these parts. For this purpose, it is essential to understand the relationship between the residual stresses and fatigue performance quantitatively as well as qualitatively. It has been widely accepted that tensile residual stresses in welded structures are as high as the material yield strength level. Therefore, the fatigue strength of welded joints is governed predominantly by the applied stress range, regardless of the load ratio. However, in stress relieved components the tensile residual stress level is not as high, and the weld fatigue behavior is more influenced by the load ratio.