Study On Interfacial Bonding Durability Of CFRP-Steel In Seawater Environment

The steel structure buildings in the ocean need to be reinforced and repaired with the extension of service time or the change of load.External paste Carbon fiber reinforced composites(Carbon Fiber Reinforced Plastic or Carbon Fiber Reinforced Polymer,referred to as CFRP)reinforcement technology,with the advantages of convenient construction,no increase in load and no introduction of residual stress,It has been widely used in the field of civil engineering.The stripping failure of CFRP-steel interface is the most important failure mode of CFRP reinforced steel structure.Therefore,in view of the marine environment,the interfacial bonding performance of CFRP-steel under seawater immersion is the key problem in the application of CFRP reinforced steel structure technology in the ocean.In this paper,the bonding properties of CFRP and steel interface under seawater immersion are studied by means of experimental research and theoretical analysis.First of all,from the material level,the study of seawater immersion,variables have soaking time(30 days,60 days and 100 days)and soaking temperature(20℃,40℃and 60℃),effect the mechanical properties of CFRP plate,structural adhesive(T1 adhesive and T_C adhesive).Then,from the component level,the effect of seawater immersion on the interfacial bonding performance of CFRP-steel was studied by double-lap test method.Based on the degradation of material properties,the law and mechanism of interfacial degradation of CFRP-steel under seawater immersion environment are revealed,which provides theoretical and scientific basis for the design of CFRP reinforced steel structure under marine environment.The main research contents and results of this paper are as follows:Through the double-lap test of CFRP-steel,the effects of two parameters of different adhesive types(T1 adhesive and T_C adhesive)and CFRP bonding length effect the interfacial failure mode,strain distribution and bonding-slip relationship of CFRP-steel were studied.The test results show that the interfacial bonding-slip relationship of linear adhesive T1 can be divided into two stages,ascending stage and descending stage,and the nonlinear adhesive T_C interface bonding-slip relationship can be divided into three stages,ascending stage,stabilization stage and descent stage.The water absorption and diffusion behavior,tensile properties test and dynamic mechanical thermal analysis of CFRP plate in seawater solution at different temperature were studied,and the action law and mechanism of seawater CFRP plate were obtained.The results showed that the fiber resin interface debonding and resin matrix were plasticized,resulting in lower performance.The water absorption and diffusion behavior,tensile properties test and dynamic mechanical thermal analysis of two kinds of structural adhesives(T1 adhesive and T_C adhesive)in seawater at different temperature were studied,and the action law and mechanism of seawater on adhesives were obtained.The results showed that water molecules entered the inside of the adhesive,causing the adhesive to be plasticized and the tensile properties to be reduced.By making 56 double-lap specimens,the effects of seawater immersion on the interfacial failure mode,load-displacement relationship,strain distribution and bonding-slip relationship of CFRP-steel were obtained.The results show that seawater immersion can reduce the interfacial stiffness,interfacial maximum shear stress and ultimate bearing capacity of CFRP-steel,and the higher the temperature,the faster the degradation of interfacial bonding performance.