Mechanical behaviors of steel-CFRP plate bonded joints after freezing-thawing cycles

The effective bonding between the steel element and carbon fiber reinforced polymer (CFRP) is critical for applying the CFRP to strengthen steel elements. The severe service environment always affects the interfacial bond strength, resulting in a reduction in strengthening efficiency. To research the interfacial bond performance between the steel element and CFRP plate after freezing-thawing environment, this paper conducted studies on the mechanical behaviors of steel-CFRP plate joints. Experiments indicated that the freezing-thawing environment did not influence the failure mode, but decreased the interfacial ultimate capacity of double-shear specimens. The ultimate load is reduced by 14.5% after exposure to 300 freezing-thawing cycles. An approximate bilinear bond-slip relationship is employed for expressing the interfacial bond-slip behavior of all specimens, and the freezing-thawing environment has a negative influence on the bond-slip behavior. By determining the degeneration laws of bond-slip parameters after experiencing freezing-thawing cycles, the bilinear bond-slip model considering freezing-thawing effect was developed. Moreover, the three-dimensional FE modelling was implemented based on the mixed-mode cohesive zone model. The comparisons of the test and FE results show that the FE results are consistent with the test results, and the interfacial damage and debonding process can also be precisely predicted. The numerical modelling also reveals that the asymmetric debonding of the two interfaces can affect the ultimate load, which leads to a higher scatter of test results for the double-shear joint.