Emergent Mechanics of Auxetic Layered Anisotropic Composite Structures

营养是一类特殊的材料，当向一个方向拉伸时，它会向另一个或两个方向扩张，而不像传统材料那样收缩。拉伸材料和结构可以通过以特定方向和顺序层叠纤维增强复合材料层来制造。与等效的非伸展结构相比，制备伸展复合结构显著提高了其能量吸收能力和抗分层能力。虽然有一些实验证据存在，但对于潜在的变形机制严重缺乏基本的了解，以利用辅助性来实现最佳的性能增强而不损害其他特性。该奖项支持基础研究，以了解伸展的层状复合材料结构的力学行为的帮助下，综合实验-建模方法。所获得的知识将使复合材料结构在飞机结构、汽车和海洋应用中具有显著改善的韧性和损伤容限，同时提供重量、成本和能源节约。这项研究促进了生长素的新用途，可能会扩展到改进的人工骨植入物、假体和防凹层压地板。此外，该奖项还将促进初中生的招生和教育，培养他们对STEM领域的热情。同时，本科生和研究生将在这一关键领域进行原创性研究，获得新的技能和人才。在开展这些活动时，将利用机构方案优先招募妇女和少数群体。伸展层状各向异性复合材料结构的性能提高从根本上归因于潜在的三轴应力状态和导致失败的独特机制。为了了解这些问题，我们将使用最先进的表征和成像技术，通过有针对性的实验来研究不同延伸性水平下的拉伸复合材料(碳纤维和碳纳米管增强聚合物基层板)的本构行为和破坏行为。这将对微观层面上的变形和破坏机制提供深入的了解。补充的微观力学方法将被用来模拟观察到的刚度退化，并开发反映物理观察行为的内聚规律。这些经过实验验证的微机械模型将被集成到使用基于能量的相场方法开发的冲击模型中。该模型的物理洞察力，以及预测伸展结构在各种载荷下的响应的能力，将使基于科学的方法得以实施，该方法使用伸缩性作为配置约束，在各种应用中实现层状复合材料结构的可控性能增强。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Auxetics are a special class of materials, which when stretched in one direction, expand in the other one or two directions, unlike conventional materials which contract. Auxetic materials and structures may be produced by laminating fiber reinforced composite layers in certain specific orientations and sequences. Producing auxetic composite structures significantly enhances their energy absorbing capability and delamination resistance, in comparison to equivalent non-auxetic structures. Although some experimental evidence exists, fundamental understanding of the underlying deformation mechanisms is severely lacking to use auxeticity for achieving optimum performance enhancements without compromising other properties. This award supports fundamental research to understand the mechanical behavior of auxetic layered composite structures with the help of an integrated experimental-modeling approach. Knowledge gained will enable composite structures with substantially improved toughness and damage tolerance for aircraft structures, automotives, and marine applications, while simultaneously providing weight, cost, and energy savings. New usages of auxetics facilitated by this research may extend to improved artificial bone implants, prosthetics, and dent-resistant laminated flooring. Furthermore, this award will facilitate recruitment and education of middle and high school students and foster their excitement about STEM fields. At the same time, undergraduate and graduate students will perform original research and attain new skills and talents in this critical area. In the conduct of these activities, the recruitment of women and minorities will be prioritized by leveraging institutional programs.The performance enhancements of auxetic layered anisotropic composite structures are fundamentally attributed to the underlying triaxial states of stress and the unique mechanics that lead to failure. To understand these issues, the constitutive and failure behaviors of auxetic composites (carbon fiber and carbon nanotube reinforced polymer matrix laminates) at varying levels of auxeticity will be examined through targeted experiments using state-of-the-art characterization and imaging. This will provide insights into the deformation and failure mechanisms at the microscopic level. Complementary micromechanical approaches will be used to model the observed stiffness degradation and to develop cohesive laws that reflect the physically observed behaviors. These experimentally validated micromechanical models will be integrated into an impact model developed using an energy-based phase field approach. The physical insights from this model, along with the ability to predict the response of auxetic structures under various loadings, will enable implementation of a science-based method of using auxeticity as a configuration constraint for achieving controllable performance enhancements of layered composite structures in various applications.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.