Fatigue properties and failure mechanisms of self-piercing riveted joints in aluminium alloy

Self-piercing riveting (SPR) is an effective joining technology for lightweight materials. In order to promote the application of SPR technology widely, two groups of SPR joints in aluminium alloy were selected to obtain the fatigue properties and the microstructure characteristics of typical failure surface of joints by the fatigue test, statistical methods, scanning electron microscopy and energy dispersive X-ray. Results show that with the reduction of fatigue load, the fatigue life stability and relative slip value of joints decline. As the stress concentration in the SPR joints with multiple-rivet (MR) is reduced effectively, compared with SPR joints with single-rivet (SR) joints, the fatigue strength of MR joints is improved by 31.36%~23.14%, and the fatigue life stability of MR joints is favorable. The primary and secondary load bearing sequences are found in MR joints, and the fatigue fracture surface is the location of primary load bearing sequence. Macroscopic fatigue failure mode of all joints is the fracture of lower sheets, and fatigue crack initiation is located at the interface between the rivet shank and lower sheet. The fretting damage region spreads from the bottom of the rivet shank toward the rivet head. Deceleration of friction function can delay the initiation and slow down the propagation of fatigue crack to improve the fatigue life of joints.