Exploring Deformation Mechanisms in Metallic Nanostructures Under Extreme Conditions of Temperature and Strain Rate

非技术描述：了解纳米晶体金属固体在极端压力和低温条件下的力学行为对工程应用非常感兴趣，包括聚变反应堆（用于替代能源），爆炸载荷和装甲（国防），以及小行星撞击（科学进步）等。 在这样的载荷下，典型的工程材料，特别是金属，即使在环境条件下通过吸收大量能量以塑性方式失效，也会以脆性玻璃状方式失效。金属的机械性能取决于共同形成其结构的晶粒的大小。通过用孤立的纳米柱模拟单个颗粒，我们将研究这些柱（以及最终的单个颗粒）是否会以延性方式变形，即使它们受到上述极端条件的影响。 如果它们在环境条件下保持相同的延展性，那么这项研究将迈出开发新金属材料的第一个重要步骤，这些材料可以彻底改变能量吸收防爆民用，核和防御结构的设计，包括个人防护设备（头盔和防弹衣）减少创伤性脑损伤。这项研究还将导致高能材料物理领域的基础科学进步。 这里提出的工作是材料科学家采用先进的纳米制造和显微镜技术之间的真正合作;物理学家使用最先进的多尺度建模策略，包括管理原子间结构和力的基本原理;机械工程师采用最复杂的光学和实验技术来表征工程固体的机械行为。 因此，它为研究生和本科生提供了跨学科科学和技术领域的优秀培训。 随着这些学生进入工作岗位，他们将比同龄人更有能力跨越界限，将基础科学和高级工程联合收割机结合起来。为了将研究理念和成果更广泛地推广到社区，该补助金资助的研究生还将参加加州大学洛杉矶分校的高中暑期研究项目。因此，该项目将支持鼓励和培训青年人才进入科学和工程领域的社会需求。 技术说明：该项目将发展理解纳米结构金属固体在极端压力条件下的力学行为，高负荷率（爆炸和爆炸），低温（低于冰点）。上述目标将通过进行一系列新颖的实验来实现，该实验由多尺度建模和透射电子显微镜（TEM）分析支持，通过加载不同长度的fcc（Cu）和bcc（Mo）金属的TEM就绪单晶纳米柱样品（50 nm至100 nm）和纵横比（直径50 nm至100 nm），在极端应力条件下，（大于20 GPa）、应变速率（高于108 s-1）和温度（低温）。提出了一种直接对纳米柱施加均匀张力的方法。 这将消除晶格摩擦和压缩下存在的局部压力效应。 当与低温试验相结合时，均匀拉伸下的加载应大大增加材料中的内应力。 这将导致新的位错成核和迁移机制，并提供进一步的见解，目前的动态性能限制这些金属。 由于非常高的内应力，这项研究可能提供有史以来第一个实验证据，在冲击固体无位错塑性。为了将研究理念和成果更广泛地推广到社区，该补助金资助的研究生还将参加加州大学洛杉矶分校的高中暑期研究项目。因此，该项目将支持鼓励和培训青年人才进入科学和工程领域的社会需求。

Non-Technical Description:Understanding the mechanical behavior of nano-crystalline metallic solids under extreme conditions of pressure and low temperatures is of great interest to engineering applications involving fusion reactors (for alternative energy), blast loadings and armors (national defense), and asteroid impacts (progress of science), among others. Under such loading a typical engineering material, notably a metal, fails in a brittle glass-like manner even though at ambient conditions it fails in a plastic fashion by absorbing substantial energy. The mechanical behavior of metals is dependent upon the size of the grains that collectively form its structure. By simulating individual grains by isolated nanopillars we will study if these pillars (and eventually individual grains) will deform in a ductile fashion even when they are subjected to aforesaid extreme conditions. If they retain the same ductility as under ambient conditions then this research would have taken the first major step to develop new metallic materials that could revolutionize the design of energy-absorbing blast resistant civil, nuclear, and defense structures, including personal protective equipment (helmet and body armors) for reducing traumatic brain injuries. This research should also lead to fundamental scientific advances in the area of high energy materials physics. The work proposed here is a true collaboration between material scientists employing advanced nano-fabrication and microscopy techniques; physicists using state of the art multi-scale modeling strategies that encompass basic principles which govern the inter-atomic structures and forces; and mechanical engineers employing the most sophisticated optics and experimental techniques for characterizing the mechanical behavior of engineering solids. As such, it provides excellent training for graduate students and undergraduates in the area of interdisciplinary science and technology. As these students go into the work force, they will be more able than their peers to cross boundaries and combine basic science and high level engineering. To bring the research ideas and results more broadly to the community, graduate students funded under this grant will also participate in the High School Summer Research Program at UCLA. This project will thus support the societal needs of encouraging and training young talents into the fields of science and engineering. Technical Description: This project will develop understanding the mechanical behavior of nano-structured metallic solids under extreme conditions of pressure, high rates of loading (blasts and explosions), and low temperature (below freezing). The above goal will be accomplished by carrying out a series of novel experiments, backed by multiscale modeling and transmission electron microscopy (TEM) analysis, by loading TEM-ready single crystal nanopillar samples of fcc (Cu) and bcc (Mo) metals of varying lengths (50 nm to 100 nm) and aspect ratios (50 nm to 100 nm in diameter) by laser-generated stress waves of sub-nanosecond rise times, under extreme conditions of stress (greater than 20 GPa), strain rate (higher than 108s-1), and temperature (cryogenic). A new method is proposed to load the nanopillars directly under uniform tension. This should eliminate the lattice friction and local pressure effects present under compression. When combined with cryogenic testing, loading under uniform tension should substantially increase the internal stress in the material. This should result in newer dislocation nucleation and mobility mechanisms and provide further insights into the present dynamic performance limits of these metals. Because of very high internal stress, this study is likely to provide the first ever experimental evidence for dislocation-free plasticity in shocked solids. To bring the research ideas and results more broadly to the community, graduate students funded under this grant will also participate in the High School Summer Research Program at UCLA. This project will thus support the societal needs of encouraging and training young talents into the fields of science and engineering.