Novel rivet in flat electromagnetic self-piercing riveting with no concave die of CFRP/aluminum structures for enhancing performance

Abstract

The self-piercing riveting (SPR) is an ideal process for joining dissimilar materials such as carbon fiber-reinforced plastics (CFRP) and aluminum alloys. However, piercing CFRP with a rivet leg causes significant damage, thereby reducing joint performance. To address this issue, this study proposes a novel process called flat electromagnetic self-pierce riveting with no concave die (FE-SPR) to join 2.0-mm-thick CFRP and 5052 aluminum alloy sheets. This method is an improvement based on traditional semi-hollow rivets to enhance structural strength and reduce CFRP damage. A comparative analysis of cross-sectional quality, quasi-static mechanical properties, forming mechanisms, and failure behavior were conducted between joints fabricated with traditional semi-hollow rivet (T-rivet) and novel semi-solid rivet (N-rivet). The results showed that the N-rivet joint, unlike the T-rive joint, exhibited upsetting deformation of the rivet shank and secondary expansion of the rivet leg. These features help suppress CFRP damage and increase undercuts. The average area of CFRP damage for T-rivet joint was 33.99 mm², 135.1 % higher than the N-rivet with 5°. The peak load and energy absorption of the N-rivet with 5° were 4154 N and 11.81 J, 18.3 % and 13.5 % higher than T-rivet joints, respectively. All joints exhibited one failure mode, characterized by rivet pull-out from the aluminum plate while maintaining adhesion to the CFRP plate. This study offers a reliable solution for lightweight multi-material structures in automotive and aerospace applications.