Study On Interface Properties Of Corroded Steel Plate Strengthened By CFRP

Although protective and structural measures have been taken for a long time in corrosive environment,the corrosion behavior of steel structures can not be avoided,which will affect the mechanical properties of structures and the effect of post-reinforcement and repair.Carbon fiber reinforced polymer（CFRP）has been widely used to reinforce steel structures because of its convenience and efficiency.However,in the process of strengthening corroded steel structures,the unique bonding mechanism formed by the bonding interface of corroded steel due to the uneven surface morphology of the corroded steel affects the reinforcement effect.In order to study the effect of corrosion on the interfacial properties of CFRP plate-steel plate,the evaluation of surface morphology parameters of naturally corroded steel plate was carried out,and the relationship between the evaluation parameters and the interfacial properties of Corroded Steel Plate Strengthened by CFRP was studied.The specific contents include the following aspects:（1）Six steel plates in industrial environment were selected and classified into six corrosion grades according to the rust layer morphology.The three-dimensional coordinate data of six steel plates were obtained by three-dimensional scanning of their surface topography.Through statistical analysis of the coordinate data,the characterization parameters S_dr and d/w were selected to characterize the surface topography of the corroded steel plates,and the relationship between the grade of the rust layer,the characterization parameters and the corrosion rate was established.It was found that the relationship curves of S_dr,d/w and rust grade increased first,then decreased,and then increased.On the whole,the S_dr and d/w in the later stage of corrosion are higher than those in the early stage of corrosion.（2）Static tensile tests were carried out on 18 CFRP/corroded steel sheet single lap specimens.The strain distribution,shear stress distribution,load-displacement curve and bond-slip relationship of CFRP sheets were obtained.The relationship between the stiffness,ultimate bearing capacity and effective bond length of the specimens and the surface morphology characterization parameters obtained in Chapter 2 was established.It is found that the relationship curves of S_dr,d/w and ultimate bearing capacity all show the trend of rising first and then decreasing.Overall,the appearance of corrosion surface morphology can increase the interfacial bond strength and ultimate bearing capacity,while the relationship curves of S_dr,d/w and stiffness show a slight decrease and then gradually increase.When S_dr and d/w are small,the stress concentration degree increases with the increase of parameters.When S_dr and d/w are larger,with the further increase of S_dr and d/w,the effective bonding area and mechanical biting force of the interface increase obviously,so the stiffness also increases.（3）Based on the three-dimensional scanning technique of surface topography and the cohesion failure criterion under mixed mode,a finite element model of CFRP/rusted steel sheet single lap specimens considering the actual surface topography of the steel sheet is established.The stress nephogram,stiffness and ultimate bearing capacity of the specimens obtained by simulation are compared with the experimental results,and the results show that they are in good agreement,which verifies the correctness of the model.Expansion analysis of the effect of elastic modulus of carbon plate glue on the ultimate bearing capacity of specimens was carried out.It was found that the increase of elastic modulus of carbon plate glue would reduce the ultimate bearing capacity of specimens under the condition of other parameters unchanged.（4）The theoretical analysis of the interface performance of single lap specimens under static tension test was carried out,and the related theoretical formulas of interface performance were deduced.The roughness parameters S_dr and d/w were substituted into the theoretical deduction formulas,and the ultimate bearing capacity,load-displacement curve,shear stress distribution curve corresponding to 90%P_u and effective bond length were obtained.Comparing the calculated values with the experimental results,it is found that they are in good agreement,which verifies the feasibility of the theoretical deduction formula.