Study On The Bond Behavior Of CFRP-Steel Interfaces Under Extreme Service Environment

Carbon Fiber-reinforced polymers(CFRP)have been widely used in the field of structural reinforcement due to its advantages of light weight,high strength and excellent durability.In recent years,the externally-bonded CFRP for strengthening steel structure has attracted more attentions and a lot of studies have been carried out.The research shows that the interfacial bond behavior between CFRP and steel plays an important role on enhancement effect.Therefore,the bond behavior of CFRP-steel interfaces becomes the basis and core research content.However,most research has focused on the short-term behavior of CFRP-steel interfaces and based on the cohesive failure in the adhesive,there are limited studies on the bond behavior of CFRP-steel interfaces under extreme service environment and based on the common CFRP delamination failure and the hybrid failure.In this paper,the bond behavior of CFRP-steel interfaces had been systematically studied based on the CFRP delamination failure and the hybrid failure under extreme service environment including freeze-thaw cycle,quasistatic cyclic load and rapid load.Main research contents and results include:(1)A series of CFRP-steel single-shear specimens were tested to investigate the effects of different adhesives types(different ultimate tensile strength and elastic modulus)and different CFRP plates types(different interlaminar shear strength)on the bond behavior of CFRP-steel interfaces.The experimental data were obtained by three-dimensional digital image correlation(3D-DIC)method,and the bilinear bond-slip relationship based on the CFRP delamination failure and the trilinear bond-slip relationship based on hybrid failure were established.According to the analysis,the interfacial bond behavior is only related to the performance of the adhesive when the hybrid failure occurs.When the CFRP delamination occurs,the interfacial bond behavior is related to the properties of the adhesive and the CFRP plate.(2)An experimental study was conducted to investigate the effects of adhesive type,adhesive thickness,CFRP plate type and CFRP plate thickness on the bond behavior of CFRP-steel interface.The CFRP-steel interfacial bond-slip theory calculation model based on the mixed failure mode was obtained,which is similar to the model based on cohesive failure in the adhesive,which is determined by the performance of the adhesive.The CFRP-steel interfacial bond-slip theory calculation model based on CFRP delamination failure mode was proposed for the first time by introducing the CFRP interlaminar shear strength and the CFRP interlaminar shear energy.The accuracy of the model was verified by comparison with experimental data.(3)A series of tests were carried out on CFRP-steel single-shear specimens under freeze-thaw cycles.The degradation law and corrosion degradation mechanism of CFRP-steel interface based on different failure modes were revealed.the key parameter degradation model of CFRP-steel interfacial bond-slip relationship under freeze-thaw cycle was established by introducing the freeze-thaw cycles damage factor.Finally,the theoretical degradation model of CFRP-steel interface bond-slip relationship under freeze-thaw cycles was proposed for the first time,and the rationality of the model was verified by comparing the interface bondslip relationship under different freeze-thaw cycles.(4)A series of the CFRP-steel single-shear specimens were manufactured to investigate the effects of bond length,adhesive thickness,adhesive type and loading procedures on the bond behavior of CFRP-steel interfaces.The damage parameter based on the reduction of interface stiffness is defined.The damage mechanism and interface limit threshold load of different types of CFRP-steel interfaces under quasi-static cyclic loading were obtained by analyzing the relationship between normalized energy dissipation and damage parameter and the relationship between normalized slip and damage parameter.(5)A series of tests were carried out on CFRP-steel single-shear specimens under rapid loading.It was found that the change of loading rate had a great influence on the properties of the CFRP plate,the adhesive and the CFRP-steel interface.Based on the influence of loading rate on the properties of various materials,the bond-slip theoretical calculation models under rapid loading of CFRP-steel interface based on CFRP delamination failure and adhesive cohesive failure mode were proposed for the first time.Finally,the accuracy of the model was verified by comparison with experimental data under different loading rates.