Collaborative Research: Cellular Metamaterials that Localize Stress - Towards a Topological Protection against Fracture

设计能够承受严重载荷条件的工程结构的主要挑战之一是开发能够智能管理应力以避免或延迟断裂的发生和传播的材料。实现这一目标的大多数传统方法涉及改善材料的微观结构组成以增加韧性。该奖项重新审视了具有蜂窝结构的晶格材料的断裂，不仅可以通过调整材料成分，还可以通过改变蜂窝结构的形态来寻求保护。重点将放在一类特殊的晶格材料上，在这种材料中，由于外部载荷，应力可能集中在已知的理想位置，从而能够防止或延迟损伤过程的发生。从这项研究中获得的知识将有助于提高从基础设施工程到航空航天工业的工程应用中结构系统的寿命和可靠性。该项目还将支持为大学生设计应力分析的创新演示工具包，并为高中生和公众演示结构分析的基本原理。该项目的目的是研究细胞超材料中的拓扑结构在管理内部应力和防止断裂方面的潜力。该项目的中心是麦克斯韦晶格，可以包含拓扑极化状态，包括拓扑保护状态的自应力沿着内部域壁或接口。当这些晶格被加载和变形时，应力倾向于主要集中在这些界面上，即使在域中存在裂纹的情况下。因此，可以避免或显著延迟通常在裂纹尖端处观察到的有害应力集中和随后的断裂。该项目将评估这种属性，这取决于晶格的散装架构，是如何保持从理想的晶格赋予完美的铰链到现实的晶格具有结构韧带。这一目标将通过基于数字图像相关性的实验表征来实现，并伴随着将拓扑断裂保护扩展到连续极限的理论发展。该奖项还将致力于确定材料本身受故障影响的拓扑保护深度，并将通过声发射监测进行实验评估。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进行评估，被认为值得支持。

One of the main challenges in designing engineering structures that can withstand severe loading conditions is the development of materials that can intelligently manage stresses to avoid or retard the onset and propagation of fracture. Most traditional approaches towards this goal involve improvements in the microstructural composition of the material to increase toughness. This award revisits fracture in the context of lattice materials featuring a cellular architecture, where protection can be sought not only by adjusting the material composition but also through changes in the morphology of the cellular structure. The focus will be on a special class of lattice materials in which it may be possible to concentrate the stresses due to external loading at known, desirable locations, providing the ability to prevent or delay the onset of damage processes. The knowledge gained from this research will contribute towards the longevity and reliability of structural systems across engineering applications, from infrastructural engineering to the aerospace industry. The project will also support design of innovative demonstration kits on stress analysis for undergraduate students and demonstrations of basic principles of structural analysis for high-school students and the public.The objective of this project is to investigate the potential of topology in cellular metamaterials in managing internal stresses and protecting against fracturing. The project is centered on Maxwell lattices that can contain topologically polarized states, including topologically protected states of self-stress along internal domain walls or interfaces. When these lattices are loaded and deformed, the stress tends to focus predominantly on these interfaces, even in the presence of cracks in the domain. As a result, the detrimental stress concentration and subsequent fracturing, which is typically observed at crack tips can be avoided or significantly retarded. The project will assess how this property, which depends on the bulk architecture of the lattice, is preserved in going from ideal lattices endowed with perfect hinges to realistic lattices featuring structural ligaments. This objective will be achieved through an experimental characterization based on digital image correlation accompanied by theoretical development that will extend the topological fracture protection to the continuum limit. Efforts will be also devoted to determining how deep into the topological protection the material itself is affected by failure, an assessment of which will be sought experimentally using acoustic emission monitoring.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.