Characterising moisture ingress in adhesively bonded joints using nuclear reaction analysis

The moisture ingress in bonded structures is usually characterised by gravimetric experiments on bulk adhesive samples. This is a relatively economic and convenient method. However, this approach poses a problem as only the total amount of moisture in the specimen can be determined and not the moisture concentration distribution throughout the adhesive layer. In this study, the moisture profile at two different ageing times (43 and 96 h) in a bonded joint has been determined by use of nuclear reaction analysis (NRA). The moisture ingress profile, which was found to be Fickian in the bulk adhesive sample, was dominated by apparent Case II kinetics in the bonded joint specimens. The ingress in the laminates was seen to be much faster than if the moisture transport had been governed by Fickian diffusion.