Understanding Hierarchy and Multi-stability in Mechanical Metamaterials for Advanced Energy Absorption

吸能材料在工程应用中是必不可少的；然而，传统材料存在固有的缺陷，限制了它们的应用。例如，泡沫是轻质的，但其内部结构的随机性使其行为很难预测。橡胶类材料的行为更容易预测，但与泡沫相比，它们并不轻。该项目将设计一种具有规则内部结构的新型泡沫状材料，以提高能量吸收的可预测性，同时保持重量轻。最重要的是，该奖项将介绍和研究新的结构特征--层次化(如骨骼)和多重稳定性(如POP管)--的影响，目的是提高能量吸收性能，包括容量、效率和方向性。提高能力和效率会产生影响，例如航空航天和汽车能力，在这些领域，空间/重量限制要求材料具有最大的单位体积/质量的能量吸收。控制吸收方向性允许根据复杂的加载环境来定制响应。了解层次化和多稳定性的影响，可以指导新材料的设计以获得优异的性能，并促进其在实践中的应用。实施这项研究还将影响本科生的教育(约100)在那里，作为课程的一部分，为了加强所学的原则，他们将为项目的实验部分做出贡献。此外，当地高中生将通过讲座和动手演示来激发他们对STEM职业的兴趣。本项目的目标是设计一种新的具有分层、多稳定内部结构的细胞超材料，并分析这些属性对固有吸收性能的影响-具体地说，其容量、效率和方向性。为了实现这一目标，该项目旨在实现三个主要目标：(I)提高吸收能力和效率，使其接近理想的吸波体；(Ii)控制吸收的方向性，使其超越周期性结构；(Iii)将最小表面/体积结构的吸收性能与其拓扑结构联系起来。一般假设，层次化和多重稳定可以协同作用来控制刚度、峰值荷载和变形范围，这些因素定义了荷载-位移滞后，影响了结构的吸收能力和效率，更不用说损伤容限了。基于旋转的捕捉元件的具体使用将向非周期设计开放蜂窝结构，从而允许吸收方向性打破传统周期晶格的旋转对称性所施加的响应。了解多稳定跳跃和层次结构对机械行为的组合的、潜在的协同作用，可以指导针对特定性能的超材料设计，并在实际环境中促进超材料的采用和实用。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。

Energy-absorbing materials are essential in engineering applications; however, conventional materials possess inherent shortcomings that limit their utility. For example, foams are lightweight, but the randomness of their internal structure makes their behavior hard to predict. The behavior of rubber-like materials is easier to predict but they are not lightweight compared to foams. This project will devise a new class of foam-like materials with a regular internal structure to improve the predictability of energy absorption while remaining lightweight. Critically, this award will introduce and investigate the impact of new structural features – hierarchy (as seen in bone) and multi-stability (as seen in pop tubes) – with the aim of enhancing the energy absorption performance, including the capacity, efficiency, and directionality. Increasing capacity and efficiency impacts, e.g., aerospace and automotive capabilities, where space/weight limitations call for a material with maximum energy absorption per unit volume/mass. Controlling the absorption directionality permits tailoring the response to the complex loading environment. Understanding the impact of hierarchy and multi-stability can guide the design of new materials for superior performance and promote their utility in practice. Executing the research will also impact the education of undergraduates (approx. 100) where, as a part of their coursework and to reinforce learned principles, they will contribute to the experimental component of the project. In addition, local high school students will be engaged with lectures and hands-on demonstrations to pique their interest in STEM careers.The goal of this project is to devise a new class of cellular metamaterials characterized by hierarchical, multi-stable internal architecture and to analyze the impact of those attributes on the innate absorption performance – specifically, the capacity, the efficiency, and the directionality thereof. In pursuit of this goal, the project aims to accomplish three main objectives: (i) to enhance the absorption capacity and efficiency toward that of an ideal absorber; (ii) to control the directionality of the absorption beyond that of periodic architectures; (iii) to link the absorption performance of minimal surface/volume architectures to their topology. In general, it is hypothesized that hierarchy and multi-stability may work in tandem to control stiffness, peak load, and deformation range that define the load-displacement hysteresis, affecting the absorption capacity and efficiency, not to mention damage tolerance. The specific use of rotation-based snapping elements will open the cellular architecture to non-periodic designs and, thus, permit the absorption directionality to break free of the response imposed by the rotational symmetry of traditional, periodic lattices. Understanding the combined, potentially synergistic, effects of multi-stable snap-through and hierarchy on the mechanical behavior can guide metamaterial design for specific performance and promote metamaterial adoption and utility in practical settings.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.