Dielectric studies of ageing in aluminium epoxy adhesively bonded structures: Design implications

Abstract

Abstract

The ageing behaviour of aluminium epoxy-aluminium, adhesively bonded structures is investigated using high-frequency dielectric analysis, mechanical shear and cleavage experiments. The joints are aged at 70 °C and 100 per cent 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 and whether or not significant corrosion of the oxide layer at the interface between the adhesive and the substrate has occurred. 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 in the joint structure as characterized by the dielectric data and the loss of mechanical strength. There is evidence of toughening due to plasticization of the adhesive from the fracture toughness data.