Electrical Impedance Characterization of Discontinuous Conductive Fiber Composites

这项工作的前提是，具有不连续、高导电纤维的复合材料的电阻抗响应可以用来表征其微观结构（纤维结合、取向、数量密度等），并监测加载时的重要变化，包括应变和永久损伤效应（如基体开裂和纤维脱粘、断裂和拔出）。这种能力对于“智能”、自我监控的结构复合材料的控制制造和部署是必要的。由于这种阻抗响应的必要要求-高导电纤维，中等导电基体和可频率切换的界面阻抗-已经确定，本项目将研究胶凝基体（水泥中的钢或碳纤维）和陶瓷基体（氮化硅中的SiC）复合材料的阻抗响应。将进行实验室“物理”模拟（例如，介电介质中的单线/光纤）、基于像素的计算机建模（与NIST合作）和实际复合研究（单纤维拉拔、整体压缩和缺口梁拉伸测试）的组合，后者将适当地用于同时测量阻抗。本项目将利用阻抗谱技术研究复合材料在加载过程中的微观结构和微观结构变化。所获得的结果应该适用于广泛的复合材料，包括水泥基，陶瓷基，甚至聚合物基系统（如果满足上述条件），并且是开发新型自监测复合材料和方法的重要的第一步。在提高我们对这些复合材料的理解的同时，阻抗谱技术将发展成为一种可靠的微观结构分析表征工具。除了培养两名材料科学与工程方面的研究生和几名本科生外，该项目的材料和经验将被纳入一门向非理工科本科生教授理工科原理的课程中。***

The premise of this work is that the electrical impedance response of composites with discontinuous, highly-conductive fibers can be employed to characterize their microstructure (fiber bonding, orientation, number density, etc.) and to monitor important changes upon loading, including strain and permanent damage effects (e.g., matrix cracking and fiber debonding, fracture and pullout). Such capabilities are needed for the controlled fabrication and deployment of 'smart', self-monitoring structural composites. Since the necessary requirements for such an impedance response-highly conductive fibers, a moderately conductive matrix, and a frequency-switchable interfacial impedance-have been identified, this project will study the impedance response of cementitious matrix (steel or carbon fibers in cement) and ceramic matrix (SiC in silicon nitride) composites. A combination of laboratory 'physical' simulations (e.g., single wire/fiber in a dielectric medium), pixel-based computer modeling (in collaboration with NIST), and actual composite studies (single fiber pullout, bulk compressive, and notched-beam tensile tests) will be carried out, with the latter appropriately instrumented for simultaneous impedance measurements. %%%This project will study the microstructure and microstructural changes during loading of composite materials using impedance spectroscopy. The results obtained should be applicable to a broad range of composites, including cement-matrix, ceramic-matrix, and even polymer-matrix systems (if the above-mentioned conditions are met) and are an important first step in the development of novel self-monitoring composite materials and methodology. As well as improving our understanding of these composites, the impedance spectroscopy technique will be developed into a reliable characterization tool for microstructural analysis. In addition to the training of two graduate students and several undergraduates in materials science and engineering, the materials and experiences from the project will be incorporated in a course teaching science and engineering principles to non-science undergraduates.***