Emergent Mechanics of Auxetic Layered Anisotropic Composite Structures

增塑剂是一类特殊的材料，当它向一个方向拉伸时，会向另一个或两个方向膨胀，这与传统材料收缩不同。纤维增强复合材料层按一定的取向和顺序叠合可产生增塑型材料和结构。与等效的非复合材料结构相比，复合材料结构的吸能能力和抗脱层能力得到了显著提高。尽管存在一些实验证据，但对潜在变形机制的基本理解严重缺乏，无法在不损害其他性能的情况下使用塑性来实现最佳性能增强。该奖项支持在综合实验建模方法的帮助下，进行基础研究，以了解失活层状复合材料结构的力学行为。所获得的知识将使复合材料结构在飞机结构、汽车和船舶应用中具有显著提高的韧性和损伤容限，同时提供重量、成本和能源节约。这项研究促进了助剂的新用途，可以扩展到改进的人工骨植入物，假肢和抗凹痕层压地板。此外，该奖项将促进初高中学生的招聘和教育，培养他们对STEM领域的兴趣。同时，本科生和研究生将在这一关键领域进行原创性研究，并获得新的技能和才能。在开展这些活动时，将利用机构方案优先考虑妇女和少数民族的招聘。缺失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破坏的独特力学。为了了解这些问题，我们将通过使用最先进的表征和成像技术进行有针对性的实验，研究在不同强度下的生长性复合材料（碳纤维和碳纳米管增强聚合物基体层压板）的本构和失效行为。这将在微观层面上提供对变形和破坏机制的见解。互补的微力学方法将用于模拟观察到的刚度退化，并制定反映物理观察到的行为的内聚规律。这些实验验证的微力学模型将被整合到使用基于能量的相场方法开发的冲击模型中。从该模型中获得的物理洞察，以及预测各种载荷下增减结构响应的能力，将能够实现一种基于科学的方法，将增减性作为配置约束，从而在各种应用中实现层状复合材料结构的可控性能增强。该奖项反映了美国国家科学基金会的法定使命，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.