3D Braided Composite Structures - Experimental Characterization and Modeling of Fracturing Behavior

三维编织复合材料是一种特殊的复合材料，其特点是纱线不仅在平面内取向，而且在厚度方向上也是如此。由于这种特殊的三维结构，这些复合材料显示出出色的机械性能，使它们成为未来轻量化部件和结构的极佳候选者。这些材料的实际应用包括但不限于汽车应用，在降低重量和油耗的同时提高汽车的耐撞性；风能技术，其出色的机械和抗疲劳性能可以导致涡轮叶片更耐用、更高效；以及航空航天结构元件，在这些应用中，它们可以替代金属承载部件。然而，这些材料的有效利用一直受到缺乏描述其力学行为的数据以及有效的设计计算工具的限制。该研究项目的总体目标是通过提供全面的实验表征以及开发、校准和验证用于设计安全和高效的3D编织复合材料结构的多尺度数值框架来填补这一知识空白。除了该项目的技术任务外，还将开展一系列旨在扩大研究对教育的影响、促进多样性、传播成果和提高社会效益的活动。这些活动将包括但不限于与高中生和研究生的小组讨论，以及访问芝加哥地区的高中。这项研究的具体目标是开发一种创新的实验方案来表征3D编织复合材料的断裂特征，并向研究人员和行业介绍一种可访问的、计算高效的3D编织复合材料结构分析工具。实验活动将解决表征复合材料软化行为的问题，并将为模型校准和验证提供完整的断裂数据。通过实验研究校准和验证的多尺度框架将用于了解材料的微观结构以及结构尺寸和几何形状的综合影响。此外，这种多尺度公式将提供以更少的实验工作分析不同3D编织结构的能力，为结构优化开辟了道路。此外，它将能够捕捉已被证明影响复合材料结构的结构尺寸效应，而这一效应通常被当前的设计程序忽视。

Three-dimensional (3D) braided composites are a particular kind of composite materials characterized by yarns oriented not only in-plane, but also in the through-thickness direction. Thanks to this peculiar three-dimensional structure, these composites show outstanding mechanical properties making them excellent candidates for the lightweight components and structures of the future. Interesting examples of practical use of these materials include, but are not limited to automotive applications in which they can increase car crashworthiness while reducing weight and fuel consumption; wind energy technologies where their outstanding mechanical and fatigue resistance performances can lead to more durable and efficient turbine blades; and aerospace structural elements in which they can substitute metallic load bearing components. However, an efficient use of these materials has been limited by the lack of data characterizing their mechanical behavior as well as efficient computational tools for design. The overarching goal of this research project is to fill this knowledge gap by providing a comprehensive experimental characterization and by developing, calibrating and validating a multiscale numerical framework for the design of safe and efficient 3D braided composite structures. The technical tasks of the project will be complemented by a wide range of activities aimed at broadening the research impact on education, promotion of diversity, dissemination of results, and enhancing society benefits. These will include, but not limited to, group discussions with high school and graduate students; and visits to high-schools in the Chicagoland area.The specific objectives of this research are to develop an innovative experimental protocol to characterize 3D braided composite fracture and to introduce an accessible, computationally efficient structural analysis tool for 3D braided composites to researchers and industry. The experimental campaign will address the problem of characterizing the softening behavior of composites and it will provide complete fracture data for model calibration and validation. The multiscale framework, calibrated and validated through the experimental investigations, will be used to gain understanding on the combined effect of the microstructure of the material as well as of structural size and geometry. Furthermore, this multiscale formulation will offer the ability to analyze different 3D braided architectures with much less experimental work, opening avenues for structural optimization. In addition, it will be able to capture the structural size effect that has been proven to affect composite material structures and it is usually overlooked by current design procedures.