CAREER: Exploiting the Dynamic Dielectric Behavior of Water to Understand and Predict Polymer Composite Damage Progression

该学院早期职业发展计划（Career）项目将通过发现下一代材料损伤演变的基本机制，专注于提高聚合物复合材料的安全性和性能。高分子复合材料使用量增长迅速；由于汽车、航空航天和民用基础设施行业对高强度、轻质材料的需求不断增加。在这些主要的户外应用中，随着时间的推移，由于机械和环境应力的复杂和综合影响，材料性能会发生变化，从而导致承载能力的丧失。对这些变化的基本理解对于整个结构生命周期的安全运行至关重要。为了获得这种理解，本研究项目中的实验方法利用了吸收大气水分子在响应损伤起始和进展时介电行为的变化。通过跟踪水分子响应振荡电磁场旋转的能力，可以测量材料化学和物理特性的早期和不可见的变化。从这些测量中得出的对损伤进展机制的新的有价值的见解将提高我们设计更坚固的材料和更好地预测即将发生的故障的能力，从而促进国家健康、繁荣、福利和国防。这项研究还将得到一项努力的补充，即为来自农村和偏远城市社区的学生提供参加北卡罗莱纳州立大学K-12暑期工程营活动的机会。将开发和实施包装和传播这些高价值教育资源的可持续流程，将其影响扩大到参加现场营地的学生之外，并提高那些可能不考虑或追求STEM职业的学生的工程知名度和知识。该研究的首要目标是推导出聚合物复合材料在热、吸湿和机械载荷耦合作用下跨空间尺度损伤进展的机理基础。支持这一目标的具体目标是：(i)描述水-聚合物相互作用与纤维增强环氧树脂的拓扑结构、纳米空隙含量、极性和湿热老化之间的联系；（ii）将吸收的分子水的响应与动态、疲劳和冲击载荷引起的多尺度损伤联系起来；（iii）使用神经网络技术提取控制损伤进展的显著变量，用于获得对损伤分子前体的机制理解；（iv）调和实验和神经网络衍生的见解与最先进的多尺度，多物理场模拟技术的物理基础。该项目将使PI能够扩展力学和材料科学的知识库，从而在多个行业中更安全、更有效地使用聚合物复合材料。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This Faculty Early Career Development Program (CAREER) project will focus on improving the safety and performance of polymer composites by discovering the fundamental mechanisms governing the evolution of damage in these next-generation materials. Polymer composite usage is growing rapidly; driven by increasing demand for high-strength, lightweight materials in the automotive, aerospace, and civil infrastructure industries. In these primarily outdoor applications, loss of load-bearing ability over time is driven by material property changes in response to the complex and combined effects of mechanical and environmental stresses. A fundamental understanding of these changes is crucial to safe operation throughout the life cycle of the structure. To derive this understanding, the experimental approach in this research project takes advantage of changes in dielectric behavior of absorbed atmospheric water molecules in response to damage initiation and progression. By tracking the ability of water molecules to rotate in response to an oscillating electromagnetic field, early and non-visible changes in the chemical and physical characteristics of the material can be measured. The new and valuable insight into the mechanisms responsible for the progression of damage derived from these measurements will improve our ability to design more robust materials and better predict impending failure, thus advancing national health, prosperity, welfare, and national defense. The research will be complemented by an effort to provide access to K-12 summer engineering camp activities at North Carolina State University for students from rural and isolated urban communities. A sustainable process for packaging and disseminating these high-value educational resources will be developed and implemented, expanding their impact beyond the students attending the on-site camps and increasing visibility and knowledge of engineering among students who may not otherwise consider or pursue STEM careers.The overarching goal of the research is to derive the mechanistic underpinnings of polymer composite damage progression across spatial scales in response to coupled thermal, hygroscopic, and mechanical loading. The specific objectives in support of this goal are to: (i) describe the link between water-polymer interaction and topology, nanovoid content, polarity, and hygrothermal aging of fiber-reinforced epoxies; (ii) connect the response of absorbed molecular water to multiscale damage induced by dynamic, fatigue, and impact loading; (iii) use a neural-network technique to extract the salient variables that govern damage progression for use in deriving a mechanistic understanding of the molecular precursors to damage; and (iv) reconcile the experimental and neural-network derived insights with the physical basis of state-of-the-art multiscale, multiphysics simulation techniques. This project will allow the PI to expand the knowledge base in mechanics and materials science, enabling safer and more efficient use of polymer composites across multiple industries.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.