Study On Tensile Properties And Residual Strength Of Unidirectional CFRP Laminates After Low Temperature Action

Compared with steel,carbon fiber reinforced epoxy resin matrix composite material(CFRP)has the characteristics of light weight and high strength,and has been widely used in the field of civil engineering.In civil engineering applications,CFRP components are inevitably affected by various harsh environmental factors,among which low temperature environment is also one of the important environmental factors.As a load-bearing member,the change in mechanical properties of CFRP after experiencing low temperature will directly affect the safety of the building.Therefore,it is necessary to study the mechanical properties of CFRP after experiencing low temperature.In this paper,low temperature temperature and low temperature action time are used as variables,and the high and low temperature test box is used to simulate the natural low temperature environment to conduct an in-depth study on the mechanical properties of CFRP laminates after low temperature action.This paper is divided into three parts: physical test,meso-damage analysis,and residual strength prediction.The research conclusions are as follows:First,this article tests the residual tensile strength of CFRP laminates after long-term lowtemperature action.Tests have shown that after a long period of low-temperature action,the tensile strength of CFRP in the same low-temperature environment increases first and then decreases with the increase of the low-temperature action time;in the same low-temperature action time,the tensile strength of CFRP decreases with the temperature It shows the phenomenon of first rising and then falling.The longer the action time,the more obvious the tendency of tensile strength to decrease with low temperature.Secondly,this paper combined numerical simulation and scanning electron microscopy to analyze the mesoscopic damage of CFRP laminates.The simulation results observed that the thermal residual stress in the composite material will be generated due to the different thermal expansion coefficients of the fiber and the resin after the action of low temperature.The existence of the thermal residual stress affects the failure mode of the composite material under load.From the simulated damage results and the SEM image of the actual composite material under load,it can be seen that residual stress is more likely to occur in the fiber accumulation area,and cracks are more likely to occur in the area where the residual stress is concentrated.The existence of cracks affects the loading of the composite material.The stress transfer at the time.Combined with the analysis of the meso-scan graph and the numerical simulation results,it is concluded that the tensile strength of the composite material decreases due to the longterm low temperature action,the thermal residual stress is greater than the ultimate strength of the fiber and resin bond Under tensile load,the rapid expansion of cracks causes the strength of the material to decrease.Finally,based on the results of the tensile test and the conclusion of the meso-analysis,this paper establishes a semi-empirical prediction model of the median aging residual strength for predicting the residual strength of CFRP after undergoing low-temperature effects.The model considers the influence of low temperature and low temperature action time on the residual strength of the composite material,and obtains the residual strength prediction value that is closer to the actual test results,which proves that the improved model is more suitable for the residual strength after CFRP low temperature action.The prediction provides a reference for the prediction of the remaining strength of CFRP under low temperature environment in the future.