The effect of glue-line voids and inclusions on the fatigue strength of bonded joints in composites

During fatigue tests on bonded joints between flat bars of unidirectional, carbon fibre-reinforced epoxy resin, it was found that joint fatigue strength could be improved significantly by eliminating the carrier in one film adhesive, and by eliminating the voids (due to water vapour emitted from the composite) in another film adhesive containing no carrier but ballotini for glue-line thickness control. Surface preparation techniques also had a significant effect and the best solution found was to grind off the resin skin from the composite, prior to bonding.