Intrinsic Residual Stresses in 3D Woven Composites: Measurement, Modeling, and Mitigation of Their Impact on Properties

三维（3D）编织复合材料是一种相对较新的材料，在航空航天、可再生能源和汽车工业中作为传统金属材料的替代品显示出巨大的前景。与传统的层压复合材料相比，该材料具有令人兴奋的性能，包括更高的韧性，大大增强的强度和更好的抗疲劳性。3D编织复合材料也可以制造成大而复杂的形状，这是以前使用层压板无法实现的。然而，增强的复杂性，负责改善性能给研究人员和工程师提出了新的挑战。研究发现，某些聚合物基三维编织复合材料在加工过程中会产生微裂纹。由于材料成分之间的性能不匹配，在固化后的复合材料冷却过程中产生的高残余应力导致了损伤的发生。该奖项支持研究，以了解控制这些残余应力的基本科学现象，它们在复合材料中的大小和分布，以及它们如何反过来影响循环载荷下的材料性能。研究将被纳入教学环境，包括课堂教学，本科生和研究生直接参与实践研究的机会。该奖项支持在三维编织聚合物基复合材料的固有残余应力的新研究。研究需要建立新的实验和数值方法，包括：1)结合电子散斑干涉和拉曼光谱的增量钻孔法用于微尺度残余应力估计；2)将纤维中实验确定的应变和材料去除（孔洞和狭缝）引起的高分辨率位移场测量与复合材料中空间变化的应力场联系起来的逆有限元分析方法；3)评估对行业标准固化周期的修改，以降低环氧基复合材料的残余应力；4)对已知残余应力大小的三维机织复合材料进行详细的力学测试，以确定其对复合材料单调力学性能和循环力学性能的影响。该项目将促进对3D编织复合材料的开发机制和策略的基本理解，以减轻残余应力和相关损伤，这将导致制造技术的改进和这些材料在广泛的工业应用中的更好性能。

Three-dimensional (3D) woven composites are a relatively new class of materials that show great promise as an alternative to the traditional metallic materials used in the aerospace, renewable energy and automotive industries. The material exhibits exciting properties including higher toughness, greatly enhanced strength, and better fatigue resistance compared to the traditional laminated composites. 3D woven composites can also be manufactured into large, complex shapes that were previously unattainable using laminates. However, the reinforcement complexity that is responsible for the improved properties presents researchers and engineers with new challenges. It has been observed that processing of some polymer matrix 3D woven composites results in development of microcracks. The damage occurs as a result of high residual stresses that develop during cooling of the composites after curing due to the mismatch in the properties between the material constituents. This award supports research to understand the fundamental scientific phenomena controlling these residual stresses, their magnitudes and distributions within the composites, and how these in turn affect material performance under cyclic loading. The research will be incorporated into teaching environments including classroom instruction, and direct involvement of undergraduate and graduate students in hands-on research opportunities.This award supports novel study of intrinsic residual stresses in 3D woven polymer matrix composites. The research calls for creation of new experimental and numerical methods including the following: 1) incremental hole-drilling method combined with electronic speckle pattern interferometry and Raman spectroscopy for microscale residual stress estimation; 2) inverse finite element analysis method to relate experimentally determined strains in the fibers and high resolution displacement field measurements resulting from material removal (holes and slits) to the spatially varying stress field in the composite; 3) evaluation of modifications to the industry-standard curing cycle to lower the residual stresses in the epoxy-matrix composites; 4) detailed mechanical testing of 3D woven composites with known magnitudes of the residual stresses to determine their effect on monotonic and cyclic mechanical properties the composites. The project will advance the fundamental understanding of the development mechanisms and strategies for mitigation of the residual stresses and related damage in 3D woven composites, which will lead to improvements in technology of manufacturing and better performance of these materials for a broad range of industrial applications.