Experimental Research On Bond Fatigue Performance Of CFRP-Steel Interfacial

With the rapid development of economy in our country, both the maintenance and reinforcement of the structure has become the one of the hot spot of concern and research in civil engineering field. Carbon Fiber Reinforced Polymer as a new type of composite materials, with its high strength and efficiency, corrosion resistance, no increase weight, convenient construction, etc., instead of the traditional reinforcement materials have gotten a lot of applications in the field of reinforcement. Relative to the concrete structure, the application of CFRP in steel structure reinforcement research is still in the early, and the fatigue failure that is one of the major failure mode of steel structure, and the brittle failure, need to reinforce. Existing research shows that the key to the cooperative work of CFRP and steel lies in its interfacial bond properties, but the research on this aspect is still limited, especially in the fatigue property of CFRP- steel interface. Based on this, the CFRP- steel double shear specimens is designed to study the interface bond properties between CFRP- steel, the main research contents can be summarized as following three aspects:(1) Fatigue peak load, fatigue valley load and curing temperature selected as the parameters,17 static loading double shear specimens and 26 fatigue loading double shear specimens are designed to studies interface bond properties between CFRP- steel. Test phenomena and failure mode are observed, and load-displacement curve, the fatigue life of the specimens, strain distribution, effective bond length of CFRP, force transmission area and interface crack propagation rate are analyzed and discussed. At the same time, how the changes of the fatigue peak load, fatigue valley load and the curing temperature affect the bond fatigue properties of CFRP- steel interface is dissused.(2) CFRP- steel interface fatigue life and its influencing factors are analyzed. Based on fatigue test results of CFRP- steel interface, the fatigue life prediction method of CFRP- steel under the coupling action of load level and curing temperature is proposed, and the empirical formula of S-N curve considering the influence of curing temperature is obtained. In addition, the secant stiffness Kf of CFRP- steel interface is defined, its evolution rule and influence factors in the process of fatigue load is discussed, and finally, referring to Palmgren- Miner's linear cumulative fatigue damage criterion, the interface fatigue damage model under room temperature curing based on secant stiffiess and damage assessment method of the model is put forward.(3) Based on the test results of CFRP- steel interface, the interface bond slip constitutive model of CFRP- steel under static load is verified and analyzed, the evolution law of interface shear stress of CFRP- steel under the action of fatigue peak load and the bond slip curves under the action of fatigue load are studied, and finally the calculation model of interfacial bond slip of CFRP- steel under the influence of load level and curing temperature is established.