Effects of mechanical properties of adhesive and CFRP on the bond behavior in CFRP-strengthened steel structures

The bond between carbon fiber-reinforced polymer (CFRP) composites and steel is a key issue in CFRP-strengthened steel structures. The determination of key parameters in the bond strength model remains debatable. We studied the bond behavior between CFRP and steel, focusing on the effects of different types of epoxy adhesive and CFRP on the failure modes, bond-slip relationships, and bond strength parameters. The results show that due to the use of various materials, some specimens fail in interface debonding characterized by brittle failure, whereas others have cohesive failure or CFRP delamination characterized by ductile failure. The bond-slip models showed gentle-slope descending branches for interfaces with ductile failure, which is missing in brittle failure. The bond-slip relationships of most specimens can be simplified as bilinear models. However, trilinear models should be used for the specimens failing in the delamination and tearing of CFRP. As for the modes of interface debonding and CFRP superficial delamination, the maximum shear stresses in the interface linearly correlate with the elastic moduli of adhesive. The nonlinear mechanical behavior of interfaces can be well simulated by a cohesive zone model.