Critical energy release rate for a CSM reinforced carbon fibre composite/steel bonding

Metal structures are usually repaired by welding. An alternative is the bonding of composite patches, like carbon fibre reinforced epoxy, over cracked or corroded sections to restore strength or stiffness. The patch repair method is especially favourable in oil and gas installations, where the sparks from welding create a fire hazard. Knowledge of the adhesive strength of the interface between the dissimilar materials is an essential part in designing and qualifying such repairs.Specimens were made by attaching a carbon laminate to a steel plate with a glass-fibre reinforced adhesive. The Double Cantilever Beam test and the End Notched Flexure test were used to measure GIC and GIIC, respectively. GIIC was crack length dependent and the interfaces show some apparent plastic behaviour ahead of the crack.The steel–adhesive interface was found to be the weak link in both failure modes. In contrast to typical laminate properties the critical energy release rate of the interface of this system was higher in Mode I than in Mode II. This behaviour could be explained by looking at the characteristics of the fracture surfaces.