Mechanical properties and failure mechanism of steel/aluminum pre-holed self-piercing riveted joints under different loading speeds and loading types: An experimental and numerical investigation

Current research lacks a comprehensive understanding of the mechanical responses of pre-holed self-piercing riveted (PH-SPR) joints under dynamic loading conditions, similar to those experienced in vehicle collisions. Thus, this study systematically evaluates the effects of hole diameters and sheet thickness on three loading types (shear, peel, cross-tension joints) across a range of loading speeds from quasi-static (3.0 mm/min) to dynamic conditions (1.0 m/s, 3.0 m/s, and 6.0 m/s). Additionally, numerical models of PH-SPR joints are developed to analyze the failure mechanisms under various loading conditions. Results indicate that under quasi-static loading, thicker sheet thickness can improve peak load and has a more significant impact on the peel joints. The decreasing rates in the peak load of the J16 group (steel sheet thickness is 1.6 mm) are higher than that of the J12 group (steel sheet thickness is 1.2 mm) as the hole diameter increases. The peak shear load shows a linear increase with loading speed due to the strain rate effect on steel under dynamic loading. The 1.2 mm steel sheet thickness and 5.5 mm hole diameter are more significantly affected by loading speed. The peak loads for shear, peel, and cross-tension joints increase with the loading speed, with cross-tension joints demonstrating a higher increasing rate. Two failure modes, interlock failure and upper sheet failure, are identified. Furthermore, failure modes are primarily influenced by hole diameter and sheet thickness, while loading type and loading speed mainly affect the sheet deformation behavior. The deformation of pre-drilled holes can lead to uneven load distribution and subsequent joint failure.