Fretting wear mechanism and fatigue behavior of titanium alloy self-piercing riveted joint

Fatigue test of self-piercing riveted joints of TA1 titanium to itself (TT), TA1 titanium to 5052 aluminum alloy (TA), TA1 titanium alloy to H62 brass (TH) was performed. The fretting wear mechanism of the joints was analyzed by using scanning electron microscope (SEM) to observe the fracture surface and fretting domain. The influence of the strength of bottom sheet on the fatigue behavior and failure mode of the joints was investigated. The results show that crack initiation area on fracture surface located in the fretting wear domain. Micro cracks were generated from the sheet of fretting domain and gradually propagated and became macro fatigue cracks, which led to the final failure of the joints. The main function of fretting debris was to relieve wear in fretting process. In general, TT joint has excellent fatigue behavior; TA joint possesses superior fatigue behavior under high fatigue load; TH joint presents superior fatigue behavior under low fatigue load. As the upper and bottom sheets possess similar strength, the dominating fatigue failure mode of the joints is rivet fracture under higher fatigue load; the fatigue failure mostly occurred through the bottom sheet under lower fatigue load. As the strength of bottom sheet is lower than that of upper sheet, the fatigue failure mainly occurred through the bottom sheet.