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.

非技术摘要当将金属成分强调到其塑性变形的程度时，许多缺陷都可以操作以允许永久形状变化。在结晶金属中，实际上意味着所有技术合金，这些缺陷称为位错。进行合作的行动，许多脱位可以同时开始移动。这个过程可能导致塑性不稳定性，从而恶化组件的结构稳定性并最终触发故障。这种类似雪崩的过程的一个主要问题是它们自发发生，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，并非常快速。结果，关于它们在时空的发展知之甚少。在这项研究工作中，PI和他的学生将揭开脱位雪崩的精确动力。我们不仅会跟踪它们的时空动力学，而且还将定义它们对温度变化的反应。这将通过具有极快响应动力学的独特微尺度和温度依赖性变形实验来完成。预计将使用实验数据测试将测试雪崩行为的一般统计和物理模型，并将提出新颖的变形模型。成功完成我们的研究将导致更好地控制结构稳定性，并推动可以预测雪崩并因此失败的数学模型的发展。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，此处的结果的重要性将远远超出金属的可塑性。为了增加国家在STEM教育中代表性不足的群体的多样性和保留，PI将在中学年龄段的固体材料领域制定一项教育计划，他将在学校的外展活动中提出，并开创了一个新的中学女子营地。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集成。技术抽象该提案将解决一个众所周知的困难问题，该问题控制金属材料的结构完整性：当地的结构性不稳定如何在时空时间播放域中进行中的局部结构不稳定？这些不稳定性是由集体缺陷动力学引起的，称为晶体中的错位雪崩。挑战在于空间限制和此类过程的短时间尺度。在温度依赖性的微尺度过力实验中，使用纳秒时间分辨率与亚纳米位移分辨率结合使用，目的是实时跟踪脱位雪崩。这将通过扩展具有MHz数据采样功能的市售纳米Indententer并将系统集成到低温恒温器中来实现。四个主要推力构成了该研究计划的核心：1）设备样本动力学的非线性建模，2）对理论预测的缩放定律的实验验证，3）阐明从间歇性塑料流到光滑的塑性流的过渡； 4）确定热激活参数的热激活参数，用于脱位参数。如果成功的话，特此生成的大型实验数据集将是开发预测材料建模的独特基础，并且可能会更好地控制默认过渡的迁移，从而可以更好地控制结构材料的强度。该项目的关键将是一种统一的实验方法，具有高度时间分辨和依赖温度的小规模变形实验，可以评估位错雪崩的速度 - 从而审查最近提出的降低过渡过渡的雪崩理论。这些努力的影响是对晶体可塑性中动态阶段的第一个实时评估，这将改善我们对最终决定金属机械稳定性或形成小金属组件的过程的物理理解。该结果通常与整体金属相关，并为进行类似的动态相变的材料建模和系统提供了许多重要参数，从晶体到颗粒材料。拆卸的雪崩特性将对位错可塑性提供粗粒的视图，该视图可以在错位动力学和组成型晶体可塑性建模之间桥接，这可能直接导致更有效的多尺度建模框架。