Experimental Micromechanics and Toughness of Heterogeneous Solids

这项研究试图了解坚韧异质材料的内部结构如何提高抗裂性，并利用这一知识来创造新的坚韧材料。通常很难将天然高韧性材料中的巧妙设计转录成合成材料，更不用说改进或优化了，部分原因是它们的复杂结构发生在许多长度的尺度上。一项系统的实验研究将在几种自然产生的材料上进行，这些材料表现出最高的抗断裂破坏能力，如木材、骨和珍珠岩。这项研究将测量这些材料在理论框架中描述它们所需的所有关键性质，该框架比通常用于描述材料行为的理论框架更复杂、更强大。这不仅将深化现有的高抗裂材料的知识，然后将使用更强大的理论框架来探索、优化和创造新的高抗裂材料。这类材料将有助于制造更坚固、更轻和更安全的部件和结构，应用于广泛的民用、制造业和航空航天应用。该项目的方法是了解和模拟高韧性微结构，并创造新型超韧性材料：通过广义连续介质理论(Cosserat弹性)来模拟微观尺度的材料响应，该理论以更丰富但仍然是连续的方式捕捉微结构的影响。一项系统的实验研究将首次确定几种天然最坚韧的材料的所有Cosserat模数：木材、骨头和珍珠层。这将揭示由Cosserat理论捕捉到的产生高韧性的关键材料微结构特征。一项密切相关的理论研究将：(I)分析确定几种天然韧性微结构的Cosserat模数；(Ii)使用Cosserat材料来表示裂纹尖端(断裂过程区)附近的材料响应，以确认这些特性导致高韧性，并允许Cosserat模数优化以产生尽可能高的韧性。这种方法通过利用从测试自然韧性材料和理论韧性优化中学习到的关键Cosserat特征，并利用这些来创建展示这些关键Cosserat特征的新型断裂韧性微观结构，从而逃避并改进仿生(大自然没有发现所有甚至可能是最好的坚韧微结构)的迷人前景。这种新的微观结构可能与天然材料的微结构有很大不同。用这种方法制造的新材料的制造和测试将证实它们的高韧性。将开展一项综合外联和教育计划，其中包括示范材料、课程改进、网络资源开发以及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.