Exploring Deformation Mechanisms in Hierarchical Metallic Nano-Lattices: Experimental and Computational Study

这项拨款的研究目的是阐明在材料和结构引起的尺寸效应相互竞争的情况下，控制材料系统整体机械性能的基本变形机制。晶体固体既表现出本征/材料尺寸效应，如多晶体的颗粒尺寸依赖强度，也表现出外部/结构诱导的尺寸效应，如单晶微柱和纳米柱的尺寸依赖强度。虽然这两种尺寸效应都是独立研究的，但宏观结构特征尺寸和微观结构特征尺寸合并的材料系统的力学响应是一个关键的开放问题，原因有两个。首先，制造和测试微米、特别是纳米级结构的实验技术错综复杂，往往需要专门的设备。其次，大多数计算模型无法描述物理现象，这既需要离散的原子描述，也需要现实的(即可通过实验获得的)时间和空间分辨率。这项研究项目将结合先进的粗晶原子模拟计算模型与新的制造和现场实验方法来合成和测试空心金属纳米桁架，这将深入了解纳米结构材料的控制变形机制和由此产生的力学性能。如果成功，这一跨学科合作研究的结果将在合成具有高度期望的性能的新材料方面产生革命性的影响，这些材料在历史上一直是以有限的组合(如硬度和重量)耦合在一起的。所获得的知识将对结构材料的发展和改进至关重要，它是一个最好的例子来说明固体中结构-性质关系的重要性，这将被包括在课堂和高中教育中。该项目将通过跨学科研究项目培训具有工程和物理背景的本科生，特别强调招收代表人数不足的群体和妇女的学生。面向K-12学生的广泛推广活动将提供参与的机会，包括为高中生提供的暑期计划，他们被邀请在实验室工作三到六周。PIS将在一个令人兴奋的跨学科领域为研究生提供培训和职业发展，将材料现象与理论和实验相结合。最后，综合和迭代的计算和实验任务将成为成功的跨学科研究的主要范例，以缩小科学学科之间的知识差距。

The research objective of this grant is to elucidate the fundamental deformation mechanisms that govern the overall mechanical properties of material systems with competing material- and structure-induced size effects. Crystalline solids have been shown to exhibit both intrinsic/material size effects, such as the grain-size dependent strength of polycrystals, as well as extrinsic/structure-induced size effects, such as the size-dependent strength of single-crystalline micro- and nano-pillars. While both types of size effects have been studied independently, the mechanical response of material systems in which macro-structural feature size and characteristic size of the microstructure merge is a key open question for two reasons. First, experimental techniques for fabricating and testing micro- and particularly nano-scale structures are intricate and often require specialized facilities. Second, most computational models fail to describe physical phenomena, which require both a discrete atomistic description and realistic (i.e. experimentally accessible) temporal and spatial resolution. This research project will combine advanced computational models for coarse-graining atomistic simulations with novel fabrication and in situ experimental methods to synthesize and test hollow metallic nano-trusses, which will give insight into the governing deformation mechanisms and the resulting mechanical properties of nano-structural materials.If successful, the outcome of this interdisciplinary collaborative research will be transformative in the synthesis of new materials with highly desirable properties, which have been historically coupled in limiting combinations (e.g. stiffness and weight). The gained knowledge promises to be essential for the development and improvement of structural materials, and it makes a prime example to illustrate the importance of structure-property relations in solids, which will be included in classroom and high school education. This project will train undergraduate students from both engineering and physics backgrounds through interdisciplinary research projects with special emphasis on recruiting students from underrepresented groups and women. Broad outreach activities geared towards K-12 students will offer opportunities to become involved, including a summer program for high school students who are invited to spend three to six weeks working in the labs. The PIs will provide training and career development for graduate students in an exciting interdisciplinary field to combine materials phenomena with theory and experiments. Finally, the integrated and iterative computational and experimental tasks will make a prime example for successful interdisciplinary research to close a knowledge gap across scientific disciplines.