Mechanical testing of adhesive, self-piercing rivet, and hybrid jointed aluminum under tension loading

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Joining technologies play a crucial role in facilitating vehicle weight reduction, while maintaining structural performance and vehicle crashworthiness. Adhesive and self-piercing rivet (SPR) joining have individually been assessed in joining multi-material structures including aluminum alloys; however, limitations include fixturing requirements for adhesive joints and non-uniform load distribution within SPR joints. Hybrid (adhesive-SPR) joining has been proposed to potentially address these limitations. Yet, there is limited data regarding the strength, stiffness and energy absorption of hybrid joints under tension loading, and a lack of quantitative comparisons between adhesive, SPR and hybrid joints. In the present study, adhesive, SPR and hybrid joints were created in aluminum H-shaped tension specimens and the joint morphologies were quantified. Joint strength, stiffness and energy absorption were compared for two aluminum sheet metal alloys and three sheet thicknesses. Adhesive joints exhibited higher strength (up to 20.5%) and stiffness (up to 422%) than SPR joints, while SPR joints demonstrated higher energy absorption (up to 352%). Hybrid joints in 3 mm sheet exhibited reduced strength and stiffness relative to adhesive joints. Importantly, hybrid joints for 1 and 2 mm sheet thicknesses demonstrated strength and stiffness comparable to adhesive joints (<8% difference), and improved energy absorption compared to adhesive (up to 336%) and SPR joints (up to 53.5%), enhancing the performance of the individual methods. The study results could facilitate identifying suitable joining method, sheet thickness and alloy type according to structural applications (e.g. intrusion prevention versus energy-absorbing structures), and support future adoption and improvement of hybrid joints.