摘要
红外成像检测方法是无损检测中的一种新技术，具有非接触性、快速、准确、直观等独特优势，具有良好的应用发展前景。它的具体检测方法分为外置热源法和内置热源法。目前常用的检测方法存在一定的局限性。在碳纤维混凝土(C F R C)的研究中发现，对碳纤维混凝土试件进行外加电压的焦耳内热源红外检测可以改善上述存在的局限性。利用碳纤维混凝土良好的导电性，通过对碳纤维混凝土试件施加较低的电压，使其产生焦耳效应，如果试件内部存在缺陷，将在表面产生温度差，从而可以利用红外热像技术进行无损检测。
本文结合实验，针对机敏混凝土结构缺陷的焦耳内热源红外无损检测过程，进行了理论分析和计算机模拟。主要工作为：
1、将机敏混凝土合理假定为宏观各向同性材料的基础上，建立了检测过程中的热、电传导相关的控制方程；并研究了几种不同缺陷周围检测过程中的电流密度、焦耳热分布规律。
2、通过有限元方法对机敏混凝土的电热场进行了模拟分析，研究电流密度、焦耳热分布及试件表面温度分布变化规律并与实验所得试件表面温度场进行了对比分析研究。
3、研究了在焦耳内热源条件下，无缺陷结构稳态热传导问题，并获得了其解析的求解方法。其关键方法是：通过将电场量引入温度场方程，作适当变换，把含内热源的热传导方程转化为不含内热源的热传导方程，然后采用分离变量法进行求解。
4、由于含缺陷的构件具有不规则几何形状，且具有复杂内热源，在进行温度场解析求解过程中遇到很大困难。通常采用数值计算，本文通过采用一定的假设条件，提出了温度场解析求解的近似方法，并对含有二维圆形空腔缺陷的试件温度场进行了求解。
The research theme of this thesis stems from the key project of national nature and science fund: SMART CONCRETE AND IT'S STRUCTURE (serial number 50238040).
Infrared thermographic Non Destructive Testing (NDT) technique as a new NDT technology has been widely and successfully used in a variety of fields for it's unique advantages: non-contact, fast, accurate, reliable, real-time and intuitional. It adopted two kinds of methods: internal heating methods and external heating methods, which have their defects in their application. On the research of CFRC, Infrared thermograph detection under Joule heat by adding voltage to the CFRC specimens is found to be a feasible and effective method of inspection, which can avoid the defects. Because of its good electrical conductivity, CFRC specimens will engender Joule effect when a relatively low voltage was added to them. If there are flaws inside, the surface temperature distribution of the specimens should be uneven. Therefore, Infrared thermograph NDT can be conducted.
Combined with experimental data, this paper conducted the theoretical analysis and computer simulation of the Infrared thermograph NDT. The main work lists as following:
1 On the condition that CFRC is an macroscopically isotropic material, the governing equations of electric and thermal conduction for the inspection were established; The current density and Joule heat distribution around several kinds of flaws were investigated
2 By FEM , the process of inspection was simulated; The current density, Joule heat and temperature distribution were also investigated, and the simulation results were contrasted with experimental data.
3 The analytical solution of steady-state temperature field with internal Joule heat generation for sound structure is firstly investigated. By adopting appropriate transformation, this paper transform the heat conduction equation with internal heat source into a non-source heat conduction equation, and then solve the problem successfully by the method of separation of variables.
4 Due to the irregular geometric boundary and the complicated internal heat source distribution, the theoretical solution of transient temperature field for specimens with flaws is very difficult. Numerical solution is mainly applied for this problem. Adopting certain assumptions, this paper presents an approximate method of obtaining the temperature field by Green's function, and gives the solution of a two-dimensional field involving a circular vacant flaw.
引文
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