Durability of CFRP-Steel Double-Lap Joints under Cyclic Freeze-Thaw/Wet-Dry Conditions

The usage of carbon fiber-reinforced polymer (CFRP) to strengthen cracked steel structures can effectively improve its bear capacity, so it has been extensively used in recent years. The degradation of interfacial bonding is one of the most important factors affecting the durability of CFRP-steel structures under a freeze-thaw(F-T)/wet-dry (W-D) environment. In this study, epoxy resin adhesive (ERA) dog-bone specimens and CFRP-steel double-lap joints (bonded joints) were prepared. F-T/W-D cycles experiment and tensile tests of the ERA specimens and the bonded joints were also performed. Under F-T/W-D cycles, the main properties of the ERA specimens and the bonded joints were examined. Results indicated that fracture failure occurred in all ERA specimens. The hybrid failure modes of fiber peeling on the surface of CFRP plate and the bonded interface peeling between the CFRP plate and ERA layer primarily occurred in the bonded joints. The failure of both of them can be considered to be brittle, which was unaffected by the F-T/W-D cycles. With increased F-T/W-D cycles, the ultimate load and tensile strength of the ERA specimens initially increased and then decreased, whereas the elastic modulus initially increased and then remained unchanged. The ultimate load of the bonded joints decreased gradually. Based on the relationship between the interfacial bond-slip parameters and the number of F-T/W-D cycles, the bond-slip model of the bonded joints was established. The proposed relationship was validated by comparing with the experimental bond-slip relationships and the predicted relationships under the F-T/W-D cycles.