Dielectric studies of adhesively bonded CFRP/epoxy/CFRP structures — design for ageing

The ageing behaviour of carbon fibre-reinforced plastic/epoxy/carbon fibre-reinforced plastic (CFRP/epoxy/CFRP) adhesively bonded structures has been investigated by the use of high-frequency dielectric analysis and mechanical shear/cleavage experiments. The joints are aged at 70°C and 100% humidity and exhibit significant loss of strength over a prolonged period of exposure. The frequency-domain dielectric data indicate the rate at which water is absorbed in the joint structure. Time-domain data indicate whether the joint cross-section has undergone significant change with exposure to the ageing environment. A good correlation appears between the extent of change of the joint structure as characterised by the dielectric data and the loss of mechanical strength. There is evidence of toughening due to plasticisation of the adhesive from the fracture toughness data. This is the third in a series of papers dealing with dielectric studies on joints. The first looked at aluminium/epoxy/aluminium joints while the second looked at aluminium/epoxy/CFRP joints.