Static strength and fatigue life of optimized hybrid single lap aluminum–CFRP structural joints

Hybrid bolted/bonded joints are used to assemble structural components, commonly made by carbon fiber reinforced plastics (CFRP), with aluminum frames. Hence, they have become common solutions in a number of modern structural applications in the industrial fields, as well as civil constructions. Unfortunately, due to the lack of understanding of the relationships between the multiple parameters of influence that characterize their mechanical performance, only limited improvement have been achieved so far over classical bonding approaches, in terms of static and fatigue strength. As a result, further studies are needed in order to better exploit the potential of hybrid bolted/bonded joints and identify optimum joint configurations. This paper describes an optimization procedure of the joints, achieved through a systematic experimental analysis of hybrid single lap aluminum–CFRP structural joints. This, analyzing the effect of overlap length, stiffness imbalance, adhesive curing as well as of size, positioning and preload of the bolt, results in a significant rise of the strength, especially in presence of high cycles fatigue loading. Also, micrographic analysis and related numerical simulations have allowed to gain a better insight into the damage mechanisms occurring during the in-service tensile loading, corroborating the highest mechanical performance of the angle-ply lay-up proposed for the CFRP adherent.