Elucidation of fatigue characteristics and fracture mechanism of friction stir spot-welded tension-shear joint steels

The fatigue life and fracture mechanism of friction stir spot welded tension-shear joints using 590-MPa class steel as a base material under constant-amplitude conditions were investigated with focus on welding dimension variations caused by tool wear. The fatigue limit of the friction stir spot welding (FSSW) joint used for this study is significantly low compared with the static tensile strength of the joint itself. It was clarified that the FSSW joint in this study exhibited two different failure morphologies regardless of the applied load level: base metal fracture and weld area fracture. Although the welding state changes due to the tool wear phenomenon that produce two types of fracture modes in relation to the welding rip diameter, they have no effect on the fatigue strength, regardless of the applied load.

Automated summary

The study investigated the fatigue life and fracture mechanism of friction stir spot welded tension-shear joints using 590-MPa class steel as a base material, focusing on welding dimension variations caused by tool wear. The fatigue limit of the FSSW joint was found to be significantly lower than its static tensile strength, showing two different failure morphologies: base metal fracture and weld area fracture. However, changes in welding state due to tool wear leading to different fracture modes related to welding rip diameter had no effect on fatigue strength regardless of the applied load.