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 mechanica l shear/cleavage experiments. The joints are aged at 70 degrees C and 100% humidity and exhibit significant loss of strength over a prolonged period o f exposure. The frequency-domain dielectric data indicate the rate at which water is absorbed in the joint structure. Time-domain data indicate whethe r the joint cross-section has undergone significant change with exposure to the ageing environment. A good correlation appears between the extent of c hange of the joint structure as characterised by the dielectric data and th e loss of mechanical strength. There is evidence of toughening due to plast icisation of the adhesive from the fracture toughness data. This is the thi rd in a series of papers dealing with dielectric studies on joints. The fir st looked at aluminium/epoxy/aluminium joints while the second looked at al uminium/epoxy/CFRP joints. (C) 2000 Elsevier Science Ltd. All rights reserv ed.