CAREER: Curing-Induced Microcracking in Thermoset Composites

该学院早期职业发展（Career）奖旨在为热固性复合材料结构制造过程的新知识做出贡献。热固性材料是一种先进的聚合物，可以用高强度纤维增强，从而制造出具有复杂结构的轻质复合材料。它们的制造过程涉及化学固化反应、热产生和热传导，导致从液体聚合物混合物到交联固体结构的相变化。在此过程中积累的应力可能导致形成非常小的裂缝，这可能导致结构的后续失效。在空间探索、风能生产以及当前和未来交通运输的关键结构部件的生产中，广泛的固化诱发微裂纹是一个关键的技术挑战。下一代高性能轻质结构的可制造性取决于制造具有增强机械性能的无损伤复杂复合材料。该奖项支持基础计算和实验研究，为开发无裂纹热固性材料、优化复合材料性能、减少制造更好的复合材料部件的时间和成本提供必要的知识。该研究项目将与教育和推广活动相结合，包括开发一个具有参与性学习活动的电子学习平台、K12暑期课程和实习，旨在扩大代表性不足群体对研究的参与，并对工程教育产生积极影响。本课题的研究目的是揭示热固性复合材料固化诱发微裂纹的基本机理。该项目将建立工艺性能关系，以预测热固性材料在微观和宏观尺度上的固化损伤机制，这将使新的制造能力成为可能。从这项研究中获得的知识将使制造商能够定制他们的工艺，以防止固化引起的损伤。该项目将测试层/层和纤维/基体性能不匹配和树脂收缩导致微开裂的假设，当材料在低于其玻璃化转变温度和胶凝后进行加工时，取决于树脂粘度和韧性。先进的多尺度过程建模技术将考虑热梯度、树脂放热反应、热机械性能不匹配、收缩和残余应力。将测试一种新的时间无关的表征技术，用于确定中间固化程度下基于非化学计量聚合物代理的材料性能。这种学习热固性树脂固化过程中本构关系的新方法将用于识别和量化制造过程中的粘弹性和粘塑性树脂性能。固化过程中的现场测试旨在验证三种材料系统的方法，包括3D编织纺织品、粘合粘合剂和用于增材制造的热固性材料。计划的结果是一个实验验证的基于物理的多尺度过程建模框架，用于设计和优化增强型复合材料，这可以通过提供材料，制造和性能之间缺失的联系来帮助复合材料行业，以防止微裂纹。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 (CAREER) award enables contribution of new knowledge related to the manufacturing process for thermoset composite structures. Thermosets are advanced polymers that can be reinforced with high-strength fibers to create lightweight composite materials with complex architectures. Their manufacturing process involves chemical curing reactions, heat generation, and heat conduction that result in a change of phase from a liquid polymer mixture to a cross-linked solid structure. Stresses built up during the process can cause very small cracks to be formed, which can contribute to subsequent failures in the structure. Extensive curing-induced microcracking is a key technological challenge in the production of critical structural components for space exploration, wind energy production, and current and future transportation. The manufacturability of the next generation of high-performance, lightweight structures depends upon fabricating damage-free complex composites with enhanced mechanical properties. This award supports fundamental computational and experimental research to provide the necessary knowledge for developing crack-free thermosets, optimizing composite performance, and reducing the time and cost to create better composite parts. This research program will be integrated with educational and outreach activities, including developing an e-learning platform with engaging learning activities, K12 summer programs, and internships that aim to broaden the participation of underrepresented groups in research and positively impact engineering education. The research goal of this project is to reveal the fundamental mechanisms of curing-induced microcracking in thermoset composites. This project will establish process-property relationships to predict curing-induced damage mechanisms in thermosets across the micro and macro scales, which will enable new manufacturing capabilities. Knowledge generated from this research will allow manufacturers to tailor their processes to prevent curing-induced damage. This project will test the hypothesis that layer/layer and fiber/matrix property mismatches and resin shrinkage cause microcracking when the material is processed below its glass transition temperature and after gelation, depending on the resin viscosity and toughness. Advanced multiscale process modeling techniques that account for thermal gradients, resin exothermic reactions, mismatch in thermomechanical properties, shrinkage, and residual stresses will be implemented. A new time-independent characterization technique for determining material properties at intermediate degrees of cure based on off-stoichiometry polymer proxies will be tested. This novel approach to learning constitutive relations of thermosets during curing will be used to identify and quantify viscoelastic and viscoplastic resin properties during manufacturing. In-situ testing during curing will aim to validate the approach for three material systems, including 3D woven textiles, bonded adhesives, and thermosets for additive manufacturing. The planned result is an experimentally-validated physics-based multiscale process modeling framework to design and optimize enhanced composites which can help the composite industry by providing a missing link between material, manufacturing, and properties in order to prevent microcracking.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.