Moisture-assisted crack growth at epoxy-glass interfaces

The double cleavage drilled compression (DCDC)test was used to measure the critical energy release rate, moisture-assisted crack growth, and fatigue threshold for epoxyÐglass interfaces bonded with and without a silane coupling agent. The DCDC specimen consists of two glass beams (either soda-lime or fused silica)bonded together with an epoxy adhesive. A through-the-thickness hole is drilled in the centre of the specimen. In the DCDC test compressive loading causes tensile stresses to develop at the poles of the drilled hole. Cracks then nucleate in the epoxyÐglass interface, extend from the poles, and propagate axially along the interface in primarily mode I loading. The resistance to moisture-assisted crack growth at untreated epoxyÐglass interfaces is significantly less than that in monolithic glass specimens. However, the resistance to oisture-assisted crack growth at silane bonded epoxyÐglass interfaces can be comparable with or greater than that in monolithic glass. Silane bonding of epoxy to glass is more effective with fused silica than soda-lime glass, with the fatigue limit of silane bonded epoxyÐfused silica interfaces being about 2.5 times greater than that for silane bonded epoxyÐsoda-lime glass. These results are discussed in terms of possible interfacial crack growth mechanisms.