Fatigue strength and fatigue fracture mechanism of three-sheet spot weld-bonded joints under tensile–shear loading

•Fatigue property of three-sheet spot weld-bonded joints was studied.•Fatigue strength was improved by combining spot-welding and adhesive-bonding.•Fatigue crack initiation was delayed because of stress reduction by adhesive.•The delayed fatigue crack initiation resulted in the fatigue strength improvement.

This paper deals with fatigue behavior of three-sheet spot weld-bonded (SWB) joints to investigate the influence of adhesive bonding on fatigue strength and fracture mechanism. From the results of tensile–shear fatigue tests, the fatigue strength of the SWB joint was higher than that of the spot welded (SW) joint. For fatigue behavior in the SWB joint, debonding between a steel sheet and adhesive propagated from an edge of bonded area to a nugget edge, and a fatigue crack initiated at the nugget edge. It was concluded that the delayed fatigue crack initiation at the nugget edge in the SWB joint resulted in the fatigue strength improvement of SW joint.