Increasing strength and fracture toughness of carbon fibre-reinforced plastic adhesively bonded joints by combining peel-ply and oxygen plasma treatments

Multifunctional surface treatment combined with mechanical interlocking and chemical bonding is one of the directions to further expand the field of surface treatment of composite materials. In this study, plasma modi-fication was conducted on the surface of carbon fibre reinforced plastic (CFRP) pretreated by peel-ply, and then comparative analyses were conducted. The adherend surface and the bonding interface were analysed from microstructure, element distribution and chemical bonding to study the strengthening mechanism. Experimental results showed that the bonding strength and fracture toughness of the joints significantly improved after oxygen plasma treatment, which removed and transformed the silicon-containing impurity and reorganised the surface groups. Surface properties of the treated specimens were also improved, as indicated by their higher surface energy values and mechanical interlocking between substrate and adhesive. Compared to plasma treatment taken individually, the CFRP bonded joints had better performance after peel ply plus plasma treatments, and there was less strength loss and higher toughness when the surface damage resulted from the long-duration plasma treatment. These findings may provide insights into solving the challenge of simultaneously increasing the strength and toughness of CFRP bonded joints.