Influence of humidity on the durability of adhesively bonded aluminium composite structures

The manufacture of an adhesively bonded structure which involves the joining of a carbon-fibre-reinforced plastic (CFRP) composite panel and an aluminium sheet is described. The thermal characteristics of CFRP composites and aluminium structures are very dissimilar. Hence careful design of the joint is required in order to achieve a bond which has the potential of durability when exposed to a high-humidity environment, such as is met in aircraft structures. The design of such a set of joint structures and their ageing in a high-humidity environment are described. The durability of the joints was assessed using high-frequency dielectric measurements as a non-destructive method and, in a parallel investigation, destructive shear strength and fracture toughness measurements were undertaken. Changes in the mechanical properties of the joints are correlated with the effects of moisture ingress into the joint structures. The joints obtained were surprisingly durable and this study implies that the design of aluminium-CFRP composite joints are a practical proposition.