Failure of CFRP-to-steel double strap joint bonded using carbon nanotubes modified epoxy adhesive at moderately elevated temperatures

The bond characteristics of double strap joints between carbon fibre reinforced polymer (CFRP) laminates and steel with carbon nanotubes (CNTs) modified epoxy, under moderately elevated temperature (23–70 °C) were studied. The effect of CNTs on the failure modes, bond interface, and bond strength were presented. Results show that increasing test temperature causes transition of failure from epoxy-CFRP interface to steel–epoxy interface and to cohesive layer in the joints with neat epoxy. The cohesive failure could be avoided in the joints with CNT-epoxy. The observations from scanning electron microscopy revealed that CNTs bridge the cracks in epoxy matrix indicating a reinforcing effect. Moreover, CNT-epoxy can provide a significant increase (about two fold) of bond strengths at moderately elevated temperatures when compared with neat epoxy. It demonstrated that the incorporation of CNTs into the bond adhesive could allow better exploiting the potential of CFRP system in strengthening of steel structures at moderately elevated temperature.