Research On Damage Of Carbon Fiber Reinforced Concrete Based On Infrared Thermography

This dissertation was supported by the Key Project 'smart concrete and structures' of National Science foundation under grants No. 50238040.The safety, reliability and durability of large concrete project, including large dam, bridge, containment vessel of nuclear power station and etc., are momentous problems relating to national economic development and national safety. However, the problems of accumulation damages and catastrophic behavior of the in being larger concrete structures and national infrastructure become very prominent. Therefore, study on monitoring and analyzing the damage of momentous concrete structures is one of the important research subjects in civil engineering.A nondestructive detection method with infrared imaging is presented by making use of the functional property of carbon fiber-reinforced concrete (CFRC). Its detection mechanism and influencing factors are analyzed with experiments, theory, and numerical analyses. Meanwhile, studies have been made to some degree on the coupling problems of force, electricity and heat potentially in real-time monitoring. The main research works and innovations of this paper are as follows:Firstly, an improved infrared imaging method is proposed and designed to detect the damage of concrete by using of the functional properties of electro-thermal carbon fiber-reinforced concrete. The feasibility of the method is verified by experiments. The detection results show that under lower DC voltage the temperature of normal areas far from defects is able to rise 1~2°C in specimen, however, the surface temperature near the defects rises greatly. Thus, it makes the infrared imaging method more powerful to inspect the defects out. At the same time, it shows that the detection results are related to the inspection time, material components and defect shape.Secondly, model for analyzing the temperature of this transient heat transfer application is constructed based on the improved infrared imaging detection method. The mechanisms influencing on the detection from the material components and the surrounding environment are studied in terms of the electrical and heat parameters of the material. The existence of macro defects and the micro characteristic of local area near the defects, which lead to the effect of inhomogeneous internal heat source, are also studied as the leading mechanism to the detection.Thirdly, the MARC finite element analysis software and subroutine program is used to analyze the model of the Joule's heating problem for the defective CFRC specimen. By comparing the numerical results with the experimental results, the feasibility of this method and the validity of the finite element simulation are verified. At the same time, large quantity of numerical results reveals the sensitivity factors of this detection method. The study provides reference for selecting and optimizing the detection scheme in practice.Fourthly, the theoretical solution with Green's function is developed to solve theJoule's heating problem and get the temperature field in the defective specimen. On the basis of analyzing the electrical field in the defective bodies with different defect shape, two-dimensional temperature field is obtained by using the Green's function solution. The computation results by programming indicate that the distribution of temperature is the same as that of actual measurement. And the mechanism of this defection is further disclosed in theory.Fifthly, microscopic mechanism of the coupling phenomenon of force, electricity and heat, which appears in real-time monitoring, is analyzed. For the situation of simply loading, the variation of effective load area is applied to describe the damage in specimen, which can reflect not only the variation of mechanical property of material, but also the variation of electrical parameter. With the damage variable in terms of effective load area, the evolvement law of electrical parameter with the damage of CFRC is established under compression load. Combining with the corresponding Mazars damage mechanical model and energy equation, the temperature field for odd coupling problem of force and electricity, electricity and heat is obtained.The study involves several science areas such as mechanics, electricity, concrete material science, heat transfer and so on. The production has significant meanings in improving the efficiency and precision of infrared nondestructive detection in concrete, and enhancing its application in the concrete construct. Moreover, it has certain guiding effect to the realization of real-time damage monitoring and the application of CFRC in key civil engineering structures.