Environmental effects on the ageing of epoxy adhesive joints

Adhesive bonded joints are exposed to a range of different environments in aerospace applications. This paper reports dielectric and mechanical analysis of aluminium-epoxy bonded adhesives joints exposed to de-ionized water, aqueous urea solution and salt water at 65 degrees C. The changes observed are the results of plasticization and corrosion. In the case of the aqueous urea solution, passivation of the oxide by the urea reduced the rate of corrosion. Sea water contains mobile ions and a new feature is detected associated with filiform corrosion. The non-polar media aviation fuel and hydraulic fluid are able to plasticize the adhesive and there is a consequent reduction in the strength of the joint. Propylene glycol, although it is polar solvent, produces limited plasticization and degradation of the joints. Dichloromethanc was very aggressive and produced a rapid loss of strength of the joints.