Experimental Micromechanics and Toughness of Heterogeneous Solids

本研究旨在了解坚韧非均质材料的内部结构如何增强抗断裂性，并利用这些知识来创造新的坚韧材料。将天然高韧性材料中的巧妙设计转录到合成材料中通常是非常困难的，更不用说改进或优化了，部分原因是它们的复杂结构出现在许多长度尺度上。将对几种天然材料进行系统的实验研究，这些材料显示出最高的抗破裂性，如木材，骨头和珍珠质。这项研究将测量这些材料的所有关键特性，以在一个比通常用于描述材料行为的理论框架中更复杂、更强大的理论框架中描述它们。这不仅会加深对现有高抗断裂材料的认识，更强大的理论框架将用于探索、优化和创造新的高抗断裂材料。这些材料将用于制造更坚固、更轻、更安全的部件和结构，用于各种民用、制造业和航空航天应用。该项目的方法是理解和模拟高韧性微观结构，并创造新的超韧性材料：通过广义连续介质理论（Cosserat弹性）模拟微观尺度材料的响应，以更丰富的方式捕获微观结构的影响，但仍然是连续的，方式。一项系统的实验研究将首次确定几种天然最坚韧材料的所有Cosserat模量：木材、骨骼和珍珠质。这将揭示关键的材料微观结构特征，如捕获的Cosserat理论，产生高韧性。密切相关的理论研究将：(i)分析确定几个这些自然坚韧的微观结构的Cosserat模量；（ii）采用Cosserat材料来表示近裂纹尖端（断裂过程区）材料响应，以确认这些特性导致高韧性，并允许Cosserat模量优化以产生尽可能高的韧性。通过从测试自然韧性材料和理论上的韧性优化中获得关键的Cosserat特征，并利用这些特征来创建具有这些关键Cosserat特征的新型断裂韧性微结构，这种方法具有逃离和改进仿生学的迷人前景（《自然》尚未发现所有甚至最好的韧性微结构）。这种新的微观结构可能与天然材料有很大的不同。以这种方式创造的新材料的制造和测试将证实它们的高韧性。将推行一项综合推广教育计划，包括示范材料、课程改进、网络资源开发、跨学科研究和培训互动。

This research seeks to understand how the internal structure of tough heterogeneous materials enhances fracture resistance and to use this knowledge to create novel tough materials. It is often very difficult to transcribe, let alone improve or optimize, clever designs in natural highly-tough materials into synthetic materials, partly because their complex structures occur over many length scales. A systematic experimental study will be conducted on several naturally-occurring materials that show the highest resistance to failure by fracturing, such as woods, bone and nacre. The study will measure all the key properties of these materials needed to describe them in a theoretical framework that is more sophisticated and powerful than the one commonly employed to describe material behavior. Not only will this deepen the knowledge of existing highly fracture-resistant materials, the more powerful theoretical framework will then be employed to explore, optimize and create new highly-fracture-resistant materials. Such materials will be useful in making stronger, lighter and safer components and structures in a wide variety of civilian, manufacturing and aerospace applications.The approach of this project is understanding and modeling high toughness microstructures, and creation of novel ultra-tough materials: model microscale material response by a generalized continuum theory (Cosserat elasticity) that captures the effects of microstructure in a richer, yet still continuum, way. A systematic experimental investigation will determine, for the first time, all Cosserat moduli for several naturally toughest materials: woods, bone and nacre. This will reveal the key material microstructural characteristics, as captured by Cosserat theory, that produce high toughness. A closely allied theoretical investigation will: (i) analytically determine Cosserat moduli for several of these naturally tough microstructures; (ii) employ Cosserat material to represent near-crack-tip (fracture process zone) material response to confirm these characteristics lead to high toughness, and to permit Cosserat moduli optimization to produce the highest possible toughness. This approach has the fascinating prospect to escape and improve upon biomimetics (Nature has not discovered all nor perhaps even the best tough microstructures) by taking the key Cosserat features learned from testing naturally tough materials, and from the theoretical toughness optimization, and employing these to create novel fracture-tough microstructures exhibiting these key Cosserat features. Such new microstructures could differ substantially from those of the natural materials. Fabrication and testing of novel materials created in this way will confirm their high toughness. An integrated outreach an education plan consisting of demonstration materials, course enhancement, web resource development, and interdisciplinary research and training interactions will be pursued.