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

近几十年来，对轻质材料和能够承受极端使用条件的材料的探索一直是材料发展的主要驱动力。陶瓷材料虽然在高温和恶劣环境中稳定，但由于其固有的脆性和与金属材料相比较低的损伤容忍度，其结构应用受到限制。一种被称为微结构材料的新兴材料为克服这一限制提供了潜在的突破。我们的初步实验结果表明，大规模的3D微结构材料，即使是由类似于主体材料的尺度的线弹性脆性母体材料制成的，也可以表现出极大的损伤容限。因此，在这个项目中，我们建议对由(陶瓷/类陶瓷)纯脆性母材制成的各种微结构材料的断裂和损伤容限有更深入的了解。我们提出的研究基于两个基本假设：(1)三维微结构的离散性质要么固有地导致裂纹桥联，要么在断裂韧性中引入局部各向异性，或者两者兼而有之，从而导致由固有脆性母材制成的微结构材料的极端损伤容限。(2)由脆性母体材料构成的三维微结构的拓扑随机性将导致损伤区域的扩散和裂纹桥接的增强，从而进一步提高损伤容限。我们提案的具体目标有两个。首先，确定了由线弹性脆性母体材料构成的大型三维周期微结构的裂纹扩展和损伤容限机制。其次，将周期微结构断裂的力学理解扩展到脆性陶瓷母材的随机微结构。这将使我们能够检验我们的假设，并解决该提案中提出的几个与技术相关的基本问题。我们建议的教育和推广计划也通过共同关注微结构材料的力学而与研究计划完全结合。经典断裂力学已经成为分析连续介质材料断裂的非常成功的理论。然而，我们的初步结果表明，这些概念并不直接扩展到离散的3D微结构材料，即使是那些由纯线弹性脆性母体材料组成的材料。特别是，微观结构的离散性使得断裂性能的标准测量和断裂测试方案不够充分。该项目将扩展对经典断裂力学和相关测试方案的传统理解，建立对损伤容限的全面机械理解，并设计一种新的方法来表征由纯脆性材料制成的各种3D微结构材料的断裂响应。此外，通过更深入地了解微结构和断裂响应之间的相关性，我们将创建断裂机理和性能图，这些图可以用于基于结构的尺寸和密度以及加载条件等参数选择最佳的微结构。该项目的主要影响在于开发了一种方法，能够在极端加载条件下发现、设计和开发轻质、耐损伤的微建筑材料。这些材料不仅在结构应用方面有潜在的用途，而且在相关的当代技术中也有潜在的用途，如能源、生物医学和微机械设备。该项目将促进损伤容限和结构完整性分析，以便在这些备受欢迎的技术中可靠地使用微建筑材料。

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.