Influence of plastic pre-deformation on the failure behaviour of self-piercing riveted joints under multiaxial loading

The increasing use of multi-material structures in body-in-white applications has increased the importance of mechanical joining technologies such as self-piercing riveting (SPR). Since formed sheet metal components often exhibit local plastic pre-deformation in the joining zone, the effect of this pre-deformation on joint performance must be assessed under realistic loading conditions. However, joint qualification is still commonly based on individual load cases, although structural joints are typically subjected to superimposed shear and peel stresses. In this study, an L-specimen geometry was adapted to SPR joints to investigate the combined influence of plastic pre-deformation and multiaxial loading. Four material combinations comprising HCT590X steel and EN AW-6014 T4 aluminium were investigated using sheets in the as-delivered condition and after pre-stretching to a plastic strain of φ = 0.1. The results show that pre-deformation generally increased the maximum shear force, particularly for mixed-material joints. Under peel loading, the material arrangement strongly affected the joint response: peel capacity decreased by up to 34% when the aluminium was die-sided, whereas it increased by up to 56% when strain-hardened steel supported the rivet foot. Under combined shear–peel loading, load transfer shifted systematically towards the shear component, and favourable effects observed under individual load cases were not necessarily retained. The findings demonstrate that pre-deformed SPR joints cannot be assessed reliably on the basis of individual load cases alone. Instead, interlock, remaining bottom thickness, failure mode, and local material changes induced by pre-deformation must be evaluated jointly.