CAREER: Spatiotemporal Avalanche Kinetics in Size-Dependent Crystal Plasticity

职业：尺寸依赖性晶体可塑性的时空雪崩动力学

基本信息

批准号：
1654065
负责人：
Nancy Sottos
金额：
$ 62.34万
依托单位：
University of Illinois at Urbana-Champaign
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-06-01 至 2021-05-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1654065&HistoricalAwards=false
关键词：
CAREER Spatiotemporal Avalanche Kinetics Size

项目摘要

Non-Technical Abstract When a metallic component is stressed to the extent that it plastically deforms, many defects operate to allow the permanent shape change. In crystalline metals, which means practically all technical alloys, these defects are called dislocations. Acting cooperatively, many dislocations can begin to move at the same time. This process can lead to abrupt plastic instabilities that deteriorate the structural stability of components and eventually trigger failure. One main problem with such collective, avalanche-like, processes is that they occur spontaneously, which means that they are hard to predict. In addition, these dislocation avalanches are confined to the nanometer scale and proceed extremely fast. As a result, very little is known about how they proceed in space and time. In this research effort, the PI and his students will unravel the precise dynamics of dislocation avalanches. We will not only track their spatiotemporal dynamics, but we will also define how they respond to changes in temperature. This will be done by unique micro-scale and temperature-dependent deformation experiments with extremely fast response dynamics. General statistical and physical models that are predicted to describe the avalanche behavior will be tested with the experimental data, and novel deformation models will be proposed. A successful completion of our research will lead to a better control of structural stability, and drive the development of mathematical models that can predict avalanches and therefore failure. Since avalanches occur in many other systems, such as earthquakes, disordered materials, or magnetism, the significance of the here-obtained results will extend well beyond plasticity of metals. In order to increase the nation's diversity and retention of underrepresented groups in STEM education, the PI will develop an educational program in the area of solid materials for the middle-school age-bracket, which he will present in outreach activities at schools, and also pioneer a new middle-school camp for girls. These interventions will be integrated with active learning techniques that the PI is currently implementing in undergraduate education.Technical AbstractThis proposal will tackle a notoriously difficult problem that controls the structural integrity of metallic materials: How do local structural instabilities proceed in the space-time-temperature domain? These instabilities are caused by collective defect dynamics, called dislocation avalanches in crystals. The challenge lies in the spatial confinement and the short time scales of such processes. Using nanoseconds time resolution in combination with sub-nanometer displacement resolution during a temperature-dependent micro-scale straining experiment, the objective will be to trace dislocation avalanches in real time. This will be achieved by extending a commercially available nanoindenter with MHz data sampling capabilities, and to integrate the system into a cryostat. Four main thrusts compose the core of this research program: 1) non-linear modeling of the device-sample dynamics, 2) experimental validation of theoretically predicted scaling laws, 3) unraveling the transition from intermittent to smooth plastic flow, and 4) determining thermal activation parameters for dislocation avalanche dynamics. If successful, the hereby generated large experimental data set will be a unique basis for the development of predictive materials modeling, and may lead to a better control of the depinning transition and thus the strength of structural materials. Key of this project will be a unified experimental approach with highly time-resolved and temperature-dependent small-scale deformation experiments that can assess the velocity-profiles of dislocation avalanches, thereby scrutinizing recently proposed theories for avalanches near the depinning transition. The impact of these efforts is a first real-time assessment of a dynamic phase in crystal plasticity, which will improve our physical understanding of a process that ultimately dictates the mechanical stability of metals, or forming of small metallic components. The results will be relevant for bulk metals in general, and provide numerous important parameters for materials modeling and systems that undergo similar dynamic phase transitions, ranging from crystals to granular materials. Unravelling avalanche characteristics will furthermore provide a coarse-grained view on dislocation plasticity that can bridge between dislocation dynamics and constitutive crystal plasticity modeling, which may directly lead to more efficient multi-scale modeling frameworks.

非技术摘要当金属部件受到的应力达到塑性变形的程度时，许多缺陷就会产生永久性的形状变化。在晶体金属（几乎所有技术合金）中，这些缺陷称为位错。通过合作，许多错位可以同时开始移动。这个过程可能会导致突然的塑性不稳定性，从而恶化部件的结构稳定性并最终引发故障。这种集体的、类似雪崩的过程的一个主要问题是它们是自发发生的，这意味着它们很难预测。此外，这些位错雪崩仅限于纳米尺度，并且进行得非常快。因此，人们对它们在空间和时间上如何进行知之甚少。在这项研究工作中，首席研究员和他的学生将揭示位错雪崩的精确动力学。我们不仅将跟踪它们的时空动态，还将定义它们如何响应温度变化。这将通过独特的微尺度和温度相关的变形实验以及极快的响应动力学来完成。预测描述雪崩行为的一般统计和物理模型将用实验数据进行测试，并提出新的变形模型。我们的研究的成功完成将有助于更好地控制结构稳定性，并推动能够预测雪崩和故障的数学模型的发展。由于雪崩发生在许多其他系统中，例如地震、无序材料或磁性，因此此处获得的结果的意义将远远超出金属的可塑性。为了增加国家的多样性并保留 STEM 教育中代表性不足的群体，PI 将在中学年龄段的实体材料领域制定一项教育计划，他将在学校的外展活动中介绍该计划，并且为女孩开创一个新的中学夏令营。这些干预措施将与 PI 目前在本科教育中实施的主动学习技术相结合。技术摘要该提案将解决控制金属材料结构完整性的一个众所周知的难题：局部结构不稳定性如何在时空温度下进行领域？这些不稳定性是由集体缺陷动力学引起的，称为晶体中的位错雪崩。挑战在于此类过程的空间限制和短时间尺度。在温度相关的微尺度应变实验中，使用纳秒时间分辨率与亚纳米位移分辨率相结合，目标是实时追踪位错雪崩。这将通过扩展具有 MHz 数据采样功能的商用纳米压痕仪并将系统集成到低温恒温器中来实现。该研究计划的核心有四个主要方向：1）设备-样品动力学的非线性建模，2）理论预测的缩放定律的实验验证，3）阐明从间歇性到平滑塑性流的转变，4）确定位错雪崩动力学的热激活参数。如果成功，由此生成的大型实验数据集将成为预测材料模型开发的独特基础，并可能导致更好地控制脱钉转变，从而更好地控制结构材料的强度。该项目的关键将是采用高度时间分辨和温度相关的小规模变形实验的统一实验方法，该方法可以评估位错雪崩的速度分布，从而审查最近提出的脱钉过渡附近雪崩的理论。这些努力的影响是对晶体塑性动态相的首次实时评估，这将提高我们对最终决定金属机械稳定性或小型金属部件形成过程的物理理解。结果通常与块体金属相关，并为经历类似动态相变的材料建模和系统（从晶体到颗粒材料）提供许多重要参数。揭示雪崩特征还将提供位错塑性的粗粒度视图，可以在位错动力学和本构晶体塑性建模之间架起桥梁，这可能会直接导致更有效的多尺度建模框架。