Fatigue behavior and failure mechanism of friction self-piercing riveted aluminum alloy 2060-T8 joints

Abstract

Friction self-piercing riveting (F-SPR) provides an enabling technology for high efficiency and reliability joining of thin-walled structures in the aviation field. However, there is still a lack of quantitative understanding of the F-SPR joints fatigue performance, hindering its engineering application. For this purpose, the forming characteristics, static mechanical and fatigue properties of aluminum alloy 2060-T8 flat die F-SPR lap joints are systematically investigated by experiments. X-ray microscope is used to conduct a non-destructive observation for the crack initiation and propagation processes in the F-SPR joint under cyclic loads. A three-dimensional finite element model is developed to further reveal its stress distribution and failure mechanism. Two typical fatigue failure modes are identified, one is the rivet shear fracture accompanied by incomplete lower sheet fracture for high load level, the other is the lower sheet fracture under the rivet tip for low load level. Different from the low load level condition, the fracture position of the lower sheet at high load level is the contact surface between the sheets outside the rivet shank, which can be attributed to the stress concentration and the severe fretting wear. Moreover, numerical simulation indicates that the stress concentration of the rivet is mainly located at the groove under the rivet cap, and the stress in the sheets is concentrated at the rivet tip and the contact surface, which could well explain the experimental results.