The Effects of Pre-bond Moisture on the Fracture Behaviour of Adhesively-bonded Composite Joints

The results of an investigation into the effects of pre-bond moisture absorbed by fibrecomposite substrates prior to bonding with various structural epoxy adhesives are presented. Substrates were bonded in the as-received condition (where substrates had been exposed to atmospheric moisture for periods of greater than three months) and were also bonded in the fully-dried condition (after drying under vacuum at 105 oC for 28 days). Additionally, substrates were conditioned by water submersion for various durations prior to bonding. Double cantilever beam tests were performed on the resulting joints to determine the adhesive fracture energy, GIC. The effect of pre-bond moisture on the glass transition temperature of the adhesive was also determined. One adhesive was shown to exhibit an extreme sensitivity to pre-bond moisture. A severe reduction in fracture energy accompanied a change in the fracture morphology and Tg. Other adhesives were shown to be relatively insensitive to the levels of pre-bond moisture introduced.