Cellular Metamaterials that Localize Stress towards a Topological Protection against Fracture

Project summary:

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 toward this goal involve improvements in the microstructural composition of the material to increase toughness. This project 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 to 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.