Fatigue characterization and crack propagation mechanism of self-piercing riveted joints in titanium plates

The fatigue characterization and failure modes of self-piercing riveted joints in titanium plates were studied experimentally. The self-piercing riveting (SPR) process was optimised to improve the forming quality, mechanical property and failure behaviour of titanium joints through the comparative trials. The crack propagation mechanisms and fretting behaviours are quite different for different failure modes and analysed in detail from macro- and micro-perspective. The static and fatigue properties are both enhanced and the failure mode of rivet fracture is avoided for the optimised joints. The failures of upper sheet fracture and lower sheet fracture occur in the fatigue tests. Heavy fretting wear exists precisely at the critical faying interfaces and results in the fatigue crack initiations. The fatigue crack initiates at the faying interface between both sheets for the upper sheet fracture and propagates to both sides of the upper sheet simultaneously. Concerning the lower sheet fracture, the fatigue crack initiates at the faying interface between the rivet and the lower sheet, and then propagates to the close side of the lower sheet in the first stage, extends to the far side in the second stage.