Emergent Mechanics of Auxetic Layered Anisotropic Composite Structures

弹性体是一类特殊的材料，当在一个方向上拉伸时，在另一个或两个方向上膨胀，而不像传统材料那样收缩。可通过以某些特定的取向和顺序层压纤维增强复合材料层来生产发泡材料和结构。与等效的非拉胀结构相比，产生拉胀复合结构显著增强了它们的能量吸收能力和抗分层性。虽然存在一些实验证据，但对基本变形机制的基本理解严重缺乏，无法使用拉胀性来实现最佳性能增强而不影响其他性能。该奖项支持基础研究，以了解拉胀层状复合材料结构的机械行为与综合实验建模方法的帮助。所获得的知识将使复合材料结构具有显著提高的韧性和损伤容限，用于飞机结构，汽车和船舶应用，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，可能会扩展到改善人工骨植入物，假肢和抗凹痕层压地板。此外，该奖项将促进初中和高中学生的招聘和教育，并培养他们对STEM领域的热情。同时，本科生和研究生将进行原创性研究，并在这一关键领域获得新的技能和人才。在开展这些活动时，将通过利用机构方案优先招聘妇女和少数民族。拉胀层状各向异性复合材料结构的性能增强从根本上归因于潜在的三轴应力状态和导致失效的独特力学。为了理解这些问题，拉胀复合材料（碳纤维和碳纳米管增强聚合物基体层压板）在不同程度的拉胀的本构和失效行为将通过有针对性的实验，使用最先进的表征和成像检查。这将在微观水平上提供对变形和破坏机制的见解。互补的微观力学方法将被用来模拟所观察到的刚度退化，并制定凝聚力的法律，反映了物理观察到的行为。这些实验验证的微观力学模型将被集成到一个影响模型开发使用基于能量的相场方法。这个模型的物理见解，沿着预测拉胀结构在各种载荷下的响应的能力，将使科学的实施-该奖项反映了NSF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。

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.