On the fracture behaviour of aerospace-grade Polyether-ether-ketone composite-to-aluminium adhesive joints

The inherently low surface energy of carbon fibre reinforced Polyether-ether-ketone (CF/PEEK) composites results in an extremely low compatibility with adhesives. This subsequently causes significant challenges in the adhesive joining of them to other dissimilar materials. Herein, the bonding surfaces of the CF/PEEK composites were treated by a high-power UV-irradiation technique prior to the adhesive bonding, with an attempt to develop hybrid composite-to-aluminium joints with excellent fracture resistance. The mode-I, mode-II and mix-mode fracture behaviour of CF/PEEK-to-aluminium joints bonded by two commercial aerospace adhesives was evaluated. Cohesive failure within the adhesive layers or substrate damage to the CF/PEEK composites were observed in all the cases. This indicated that the adhesion between the CF/PEEK composites and the adhesives was sufficient to prevent an adhesive failure at the composite/adhesive interfaces under different fracture modes. This study explored an effective route to develop strong and tough CF/PEEK-to-aluminium joints for aerospace applications. Additionally, it revealed that the form of the adhesive supporting carrier was a key factor affecting the fracture behaviour and fracture energies of the adhesive joints.