Hybrid joints: Evaluation of the increase of the mechanical performances with respect to simple joints

Hybrid joints allow to bring together the advantages of bonded joints (i.e. lightweight design, cost reduction and higher energy absorption in case of impact loading) with the confidence, the high specific strength and well know production process of traditional mechanical joining technologies like welding, riveting and clinching. In this way, higher performances in terms of strength, stiffness and energy absorption are achieved with respect to simple adhesive, welded or fastened joints, while costs can be reduced with respect to welding or fastening and the manufacturing process is facilitated with respect to adhesive bonding. Many works deal with the static [1-4] and fatigue [5, 6] characterization of hybrid joints, and they point out higher mechanical properties in comparison with simple joints. The reason is found in a synergistic effect of the joining techniques [7] and in a more favourable stress distribution [8, 9]. In this work an extensive experimental campaign was carried out in order to compare the strength of weld-bonded, clinch-bonded and rivet-bonded joints with that of the related non-hybrid joints, evaluating also the influence of geometrical and environmental factors. The experimental analysis was conducted using the Design of Experiments (DoE) methodology, taking the maximum load (F max), the stiffness (K) and the energy absorption prior to the failure (E n) as objectives.