基于电磁层析成像和边界元法的CFRP导电特性研究

Carbon fiber-reinforced plastic (CFRP) is a kind of advanced composite material with excellent mechanical property. It has attracted extensive attention in large aircraft manufacturing industry. But the study of its anisotropic electromagnetic property lags behind the study of other properties. As one of the most important electrical parameters, conductivity plays a key role for the overall performance of CFRP. In this proposal, the conductive mechanism will be discussed in depth and the self-sensing detection will be developed based on the research results. Firstly, the structure of CFRP is analyzed in detail to investigate the formation mechanism of the electric channels in single layer structure and laminar structure respectively. Next, combining with improved boundary element method (BEM), the boundary integral equations based on the scalar potential will be built considering the inhomogeneity and anisotropy of CFRP and the main computational problems arisen in the solution procedure will be dealt with. So far, the forward model is built of which the accuracy is the prerequisite for the detection of CFRP. Develop the image reconstruction algorithm to make the conductivity distribution visual. Finally，the electromagnetic tomography (EMT) is used to analyze the magnetic field distribution inside and outside of the CFRP specimen. By optimizing the excitation model and sensor structure, the BEM model of conductivity is used to identify the defect information. The application of EMT and BEM into CFRP electric test will be studied intensively in the proposal. The pattern of the CFRP conductivity distribution is derived and validated. It is hoped that this project will open up the prospect of applying EMT to measure CFRP and provide essential analysis and foundations towards studying the structure and property of CFRP.

碳纤维增强塑料（CFRP）具有优良的机械性能，在大型飞机制造上的应用日益广泛。作为最重要的电学参数之一，电导率对于CFRP的整体性能具有关键作用。本项目拟开展相关研究，深入分析CFRP的导电机制，将其用于CFRP的自传感检测。首先建立CFRP微观结构与宏观电学性能的定量关系，探讨单层结构和层压结构中导电通道的形成原理；然后结合改进的边界元法（BEM），分析不均匀性对边界条件的影响，根据电各向异性建立基于标量磁势的电导率模型，对求解过程的关键计算问题进行探讨，改进图像重建算法，实现电导率参数分布可视化；最后采用电磁层析成像技术（EMT），优化激励模式和传感器阵列电极结构，分析CFRP内外磁场分布规律，进行缺陷信息反演；项目将深入研究各向异性和非均质材料的奇异积分求解问题，提出基于标量磁势的快速模型建立方法。不仅着眼于EMT在工业应用的扩展，而且是对CFRP这类重要复合材料新的测试方法的探索。

碳纤维增强塑料（Carbon Fiber Reinforced Polymer，CFRP）在航空航天领域的应用日益广泛，尤其是大飞机制造业中，CFRP甚至成为某些部件的主要结构材料。在使用过程中，由CFRP作为主体材料搭建的结构面临着疲劳损伤、雷电冲击、电磁兼容及电磁屏蔽要求等一系列问题。通过对导电特性的研究实现对CFRP材料的健康监测以及研制高导电的新型CFRP复合材料具有重要意义。CFRP由碳纤维和树脂聚合物构成，由于碳纤维具有导电性和方向性，而树脂基体具有绝缘特性，故CFRP电导率具有明显的各向异性。本项目针对CFRP单层板和层合板构件，提出了基于电磁层析成像技术（Electromagnetic Tomography，EMT）和边界元法（Boundary Element Method，BEM）的电导率解析方法，主要研究内容包括：(1)结合CFRP板微观结构和宏观电导率关联，深入研究其内外区域电磁场分布情况，推导基于标量磁势的边界积分方程；(2)基于电磁检测系统的CFRP电导率逆问题研究，优化CFRP生产的后续质量和损伤监测环节；(3)搭建数字式多频EMT无损检测系统，对CFRP样品进行自动扫描探伤，提高检测的有效性和效率。现阶段完成成果有：(1)以标量磁势为基本变量，构造边界积分方程，描述CFRP内部涡流规律，针对求解过程的基本解、坐标变换及奇异积分等进行探索；(2)根据所设计的电磁检测系统，充分挖掘各向异性电参数分布特征，提取CFRP试件结构损伤的几何特征、位置特征，初步实现在线实时探伤检测；(3)结合常见材料结构缺陷，优化电磁传感器设计，融合缺陷信号信息，通过上位机LabVIEW界面实现实时显示，进一步验证检测方法的有效性。该项目所采用的的方法具有非侵入非接触、响应速度快等优点，可以提高检测效率，节约维护成本，缩短研制周期。通过对CFRP导电特性的研究，为CFRP试件的无损检测、寿命预估以及CFRP材料的技术更新提供了新的思路。