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

摘要

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.