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，其特征在于纱线不仅在平面内，而且在整个厚度方向上取向。由于这种独特的三维结构，这些复合材料显示出出色的机械性能，使其成为未来轻质部件和结构的优秀候选者。这些材料的实际应用的令人感兴趣的例子包括但不限于汽车应用，其中它们可以增加汽车耐撞性，同时减少重量和燃料消耗;风能技术，其中它们出色的机械和抗疲劳性能可以导致更耐用和有效的涡轮机叶片;以及航空航天结构元件，其中它们可以替代金属承载部件。然而，这些材料的有效使用受到缺乏表征其机械行为的数据以及用于设计的有效计算工具的限制。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，校准和验证安全有效的3D编织复合材料结构设计的多尺度数值框架来填补这一知识空白。该项目的技术任务将得到一系列广泛活动的补充，这些活动旨在扩大研究对教育的影响，促进多样性，传播成果，并提高社会效益。这些将包括，但不限于，与高中和研究生的小组讨论，并访问在芝加哥地区的高中，这项研究的具体目标是开发一个创新的实验协议，以表征三维编织复合材料断裂，并介绍了一个可访问的，计算效率高的结构分析工具，三维编织复合材料的研究人员和工业。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分析不同的3D编织结构的能力，而实验工作要少得多，为结构优化开辟了途径。此外，它将能够捕捉到结构尺寸效应，已被证明会影响复合材料结构，它通常被忽视，目前的设计程序。

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.