Surface preparation effects on mode I testing of adhesively bonded composite joints

The determination and significance of surface preparation on the long-term durability of bonded composite joints is addressed. Several potential factors are evaluated, including the effects of release fabric (sometimes incorrectly referred to as a peel ply) usage and grit blasting on the fracture toughness and failure modes of bonded assemblies. The double cantilever beam (DCB) test is adapted with the intent of developing a quantitative interpretation of a composite version of the wedge test. This well-established wedge test is used for quality and durability assessments of metal bonded systems. In conjunction with conventional lap shear and joint subcomponent testing, this research is directed at enhancing the reliability of composite bonded assemblies that are subjected to long-term loading and varying environmental exposure. DCB tests show that curing nylon release fabrics against adherend surfaces leads to interfacial failures and intermittent crack propagation, with reduced loads and crack opening displacements, giving critical strain energy release rates (G(Ic)) lower than bonds produced with equivalent PTFE vacuum bag surfaces. Grit-blasted adherends have higher failure load and G(Ic) values than nonblasted ones, though the mode of failure does not change.