CMMI-EPSRC: Damage Tolerant 3D micro-architectured brittle materials

The search for materials that are lightweight and can withstand extreme service conditions has been a major driving force for material development in recent decades. Ceramic materials, while stable at high temperatures and in harsh environments, are limited in their structural applications due to their inherent brittleness and low damage tolerance compared to their metallic materials. An emerging class of materials referred to as micro-architectured materials offer a potential breakthrough to overcome this limitation. Our preliminary experimental results suggest that large-scale 3D micro-architectured materials, even when made from linear elastic brittle parent materials at scales that resemble bulk materials can exhibit extreme damage tolerance. Thus, in this project we propose to develop a deeper understanding of fracture and damage tolerance in a wide variety of micro-architectured materials made from (ceramic/ceramic-like) purely brittle parent materials. Our proposed research is based on two underlying hypotheses: (1) The discrete nature of the 3D micro-architectures either inherently gives rise to crack-bridging, introduces local anisotropy in the fracture toughness or both that leads to the observed extreme damage tolerance of micro-architectured materials made of inherently brittle parent materials. (2) The topological stochasticity in the 3D micro-architectures made of inherently brittle parent materials will result in diffused damage zones and enhanced crack-bridging, leading to further increase in damage tolerance. The specific objectives of our proposal are twofold. First, ascertain the crack growth and damage tolerance mechanisms of large-scale 3D periodic micro-architectures made of linear elastic brittle parent materials. Second, extend the mechanistic understanding of fracture in periodic micro-architectures to stochastic micro-architectures made of brittle ceramic parent materials. This will enable us to test our hypotheses and address several fundamental questions of technological relevance that are raised in this proposal. Our proposed education and outreach plans are also fully integrated with the research plan through a common focus on mechanics of micro-architectured materials.

Classical fracture mechanics has been a highly successful theory for analyzing fracture of continuum materials. However, our preliminary results indicate that these concepts do not directly extend to discrete 3D micro-architectured materials, even those made of purely linear-elastic brittle parent materials. In particular, the discreteness of the microstructure renders standard measures of fracture properties and fracture testing protocols inadequate. This project will expand upon the traditional understanding of classical fracture mechanics and associated testing protocols by developing a comprehensive mechanistic understanding of damage tolerance and devising a novel methodology to characterize fracture response of a wide variety of 3D micro-architectured materials made from purely brittle materials. Furthermore, by gaining a deeper understanding of the correlation between micro-architecture and fracture response, we will create fracture mechanism and performance maps that can be used for selecting an optimum micro-architecture based on parameters such as size and density of the structure and loading conditions.

The project's main impact lies in the development of a methodology that will enable the discovery, design, and development of lightweight, damage-tolerant micro-architectured materials for extreme loading conditions. These materials have potential uses not only in structural applications but also in relevant contemporary technologies such as energy, biomedical and micromechanical devices. This project will facilitate damage tolerance and structural integrity analysis for reliable use of micro-architectured materials in these highly sought-after technologies.