Study On Shear Behavior Of Bonding Interface Between CFRP And Steel Plate Under Variable Temperature Field

Carbon Fiber Reinforced Polymer?CFRP?is used to strengthen the steel structure due to its light weight,high strength and easy construction.The steel members after strengthened with CFRP form a solid whole.The load that is originally carried by the steel structure is pratially transferred to the CFRP through the action of the adhesive,and the steel structure and the CFRP are jointly accepted,so that the concentration of stress is avoided to a certain extent.The stress distribution is more uniform,which significantly improves the strength and bearing capacity of the steel structure.Moreover,the construction is simple and convenient,and the cost and maintenance cost are low.However,in order to apply this composite strengthening method to practical engineering,it is necessary to ensure a very good bonding performance between CFRP and steel members.The weak link of steel structure strengthened by CFRP is the adhesive between steel members and CFRP interface.Therefore,it is especially important to study the way that the load is transferred through the adhesive layer and the mechanical properties of the adhesive.In the practical engineering application of CFRP strengthening steel structure,the strengthened structure is greatly affected by the changes of external environment temperature and load.At present,domestic and foreign scholars have studied the steel structure strengthened by CFRP widely,but the influence of temperature is rarely considered,especially the influence of low temperature environment.At the same time,the technical regulations of FRP strengthening concrete structure and steel structure do not provide corresponding regulation and guidance for temperature variables.It is urgent to draw relevant conclusions through theoretical analysis and relatively new test methods to make up for the lack of research on the mechanical properties of CFRP strengthening steel structure under different temperature environments.In this paper,the bonding shear experiment of CFRP and steel plate under variable temperature field is carried out to study and analyze the bonding mechanism,failure mode,ultimate load and bonding shear stress of CFRP strengthening steel plate.The main research contents and conclusions include the following aspects:1.Based on theoretical analysis,the calculation formula of the relationship between the shear stresst_a and the external load P of the bonding interface is deduced.Based on the experiment principle of the bonding shear stress,the derivation formula of the relationship between the shear stresst_a of the bonding interface and the straine_f on the CFRP plate is obtained.Furthermore,the calculation formula of the relationship between the ultimate loadP_maxof the CFRP strengthened steel plate specimen and the strain value on the CFRP plate is obtained.The calculated value is compared with the experimental value,and the results show that the calculated value is in good agreement with the experimental value.2.By controlling the temperature design parameters,the tensile test was carried out on five specimens of CFRP plate strengthened steel plate,and the ultimate load,displacement,strain value and failure characteristics of each strain measurement point were measured,and then the characteristics and rules of strain on the surface of CFRP plate and shear stress distribution on the bonding interface were obtained.The experimental results and theoretical analysis show that:1)Temperature has a significant effect on the ultimate load of specimens.With the room temperature of 30°C as the standard,the ultimate load shows a decreasing trend with the increasing and decreasing of temperature,and the maximum is 308.8KN at30°C.2)With the change of temperature field,the failure modes of specimens also change correspondingly.At-20°C,the failure of the adhesive layer,debonding damage of CFRP and adhesive layer occur mainly.In the range of 0°C to 45°C,the failure of the adhesive and CFRP interlayer debonding failure occur mainly.At 60°C,the failure of the adhesive layer,debonding damage of steel plate and adhesive layer occur mainly.Compared to CFRP interlaminar failure,adhesion failure at steel/adhesive interface,and adhesion failure at CFRP/adhesive interface,the cohesion failure in adhensive is the most ideal failure mode for CFRP-strengthening steel components.3)Taking 100KN load as a reference,at lower temperature fields?-20°C and 0°C?,the slope of strain distribution near the length of intermediate defect on CFRP plate is larger,which indicates that there is a higher stress concentration in this area,which is usually attributed to the higher stiffness of the adhesive layer than other temperatures.In contrast,at higher temperature fields?45°C and 60°C?,the stress distribution on the adhesive layer is smoother,which indicates that the reduction of the stiffness of the adhesive layer decrease the stress concentration near the length of the intermediate defect.Meanwhile,under different temperature fields,the shear stress at the bonding interface of the specimen is greater than that at the end,and decreases along the bonding length.4.The general finite element analysis software ABAQUS was used to simulate the experiment process and stress state of steel plate strengthened by CFRP under the temperature field of 30°C.The results of finite element calculation show that the finite element model has the largest peak shear stress at the bonding interface under the ultimate load measured by the experiment,which is 36.33MPa.Compared with the measured value,the deviation is 4.57%.Meanwhile,the shear stress of the bonding interface at the defect is larger than that at the end,and decreases along the bonding length.This is agreement with the theoretical analysis and experimental results,which verifies the accuracy of the experimental results and the rationality of the derived formula.