Investigation of moisture ingress into adhesive bonded structures using high frequency dielectric analysis

The effects on the dielectric characteristics of aluminium-adhesive bonded joint structures with different surface treatments on exposure to moisture at elevated temperatures are reported. Analysis of the frequency domain data as a function of the exposure time allows th ree major ageing processes to be identified; plasticization of the adhesive, changes in the state of interfacial oxide and generation of disbonded areas. Time domain data allows identification of regions where changes in the characteristics of the bond have occurred and complements the data obtained from frequency domain data. Mechanical tests on joints aged for 733 days indicate a large decrease in the shear strength has occurred consistent with the detection of marked changes in the dielectric traces. Anodization of the substrate increases the durability of joints in comparison with etched samples. This study illustrates the potential of this method for in-situ characterization of changes occurring both within the adhesive and the adhesive substrate interface.