Predicting Dynamics in Unstable and Active Solids

该奖项支持计算和理论研究和教育。在这项研究中，理论和计算机模拟将用于预测类固体材料如何移动和失效。它关注的是无序的材料，即组成部分都混杂在一起的材料，因为人们还没有很好地理解这些材料是如何失效的。这种具有重要社会意义的材料失效事件的例子随处可见——从塑料容器或粮仓破裂到雪崩和泥石流。通过了解这些材料在失效时的行为，我们将能够更好地预测失效事件，并合理地设计材料，以精确的、预编程的方式抵抗失效或失效。此外，世界各地的实验室正在开发一类新的活性物质材料，其组成部分可以自行移动。然而，当组成部分紧密地挤在一起时，这些材料是如何流动和失效的，目前还没有成熟的理论。该项目旨在确定新的活性物质固体和处于失效过程中的非活性固体之间的相似性，以更好地预测活性固体的行为。另一个目标是设计或工程无序活性固体，使其以可编程的方式移动以执行任务。由动物或人组成的群体可以被认为是一种活跃的“实体”。密集的人群表现出固体状材料的许多特征，包括支持由人群密度的微小变化组成的波的能力，这些波在普通材料中被称为声波，以及可能导致破碎的危险故障事件。然而，由于人群在任何时候都在积极地移动，现有的静态固体理论不能应用于他们。本研究将开发一套新的理论和计算工具来模拟活跃物质群的失效。这项工作的长期目标是了解哪种类型的人群结构更有可能导致局部碾压事件，并开发预测和预防此类事件的工具。最后，这个项目将有助于教育和专业发展的跨学科的科学家和工程师的广泛管道。它将支持正在进行的努力，通过专业发展规划扩大包括女性在内的代表性不足群体在STEM领域的参与，并支持PI为跨学科物理细胞生物学课程的高年级本科生和研究生开发新的“活性物质”模块。该奖项支持理论研究和教育。PI旨在开发一个广泛的理论和计算框架，用于预测不稳定和活性固体的动力学，通过开发和扩展先前开发的方法，使用振动模式来预测稳定无序材料的变形。第一个目标是使用一种新的计算方法来量化雪崩或灾难性破坏事件中不稳定无序固体的局部变形和法向模态。这些数据将用于开发一个分析连续体模型，该模型可以预测脆性和延性破坏，并结合弹塑性和剪切转换区模型的特征。第二个目标是阐明剪切颗粒物质和主动自推进颗粒之间的新生联系，使用一种新的计算技术。第三个目标是基于“兴趣点”人群创建稳定的有源物质模拟，并将其与具有人工外部电位的非有源模拟相匹配，作为将振动模式分析直接扩展到有源系统的易于处理的起点。这将使模拟逐渐偏离稳定的活性固体，从而产生一个理论框架，可以准确预测人类群体和其他活性物质系统的密度波动。该项目将通过确定在非常高密度的驱动或活动系统中可能存在的新型材料行为来推进知识。与活性气体或流体不同，这些高密度的不稳定和活性固体可以传递剪切应力，表现出强烈的各向异性行为，并可能存储记忆。初步数据表明，这些新方法可用于预测活跃或不稳定雪崩系统的动力学和行为，这将代表一种系统的方法来合理设计活性固体，以表现出特定的流变行为或完成任务。第二个重点将集中在定量比较剪切颗粒系统和活性物质的新想法上，以便了解从经过充分研究的剪切系统中得出的哪些想法可以用于预测活性物质，以及剪切系统和活性系统之间存在哪些需要新理论的重要差异。总之，这将允许开发一个分析连续体模型，用于预测剪切和活性物质系统中的雪崩和不稳定性。这项工作适用于具有重要社会意义的问题。粒状材料和结构玻璃中的雪崩和灾难性脆性破坏在工业和自然界中都很重要——这里开发的工具用于约束基于微观材料特性的连续体模型，可以提高科学家预测地震和滑坡动力学的能力，并有助于合理设计更好的结构材料。这笔资金还将通过培训和指导女性科学家，包括系统的一系列针对女性的专业发展活动，为扩大STEM参与的社会目标做出贡献。作为该提案的一部分，PI还将开发一个活动物质模块，其中包括讲座材料，主动学习练习和一个小组研究项目，该项目将部署在高年级本科生和研究生的课程中。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports computational and theoretical research and education. Theory and computer simulations will be used in this research to predict how solid-like materials move and fail. It focuses on materials that are disordered – where the constituent parts are all jumbled up – because there is not yet a good understanding of how such materials fail. Examples of such societally important material failure events are everywhere – ranging from rupture of a plastic container or grain silo to avalanches and mudslides. By understanding how these materials behave while they are failing, we will be able to better predict failure events and rationally design materials that resist failure or fail in precise, pre-programmed ways. In addition, a new class of active matter materials, where the constituent parts can move by themselves, are being developed in labs all over the world. However, there are no well-established theories for how those materials flow and fail when the constituent parts are tightly packed together. This project seeks to identify similarities between new active matter solids and non-active solids that are in the process of failing, to better predict the behavior of active solids. An additional goal is to design, or engineer disordered active solids to move in a programmed way to execute tasks. Crowds composed of animals or humans can be thought of as a type of active “solid”. Dense human crowds exhibit many of the features of solid-like materials, including the ability to support waves composed of small changes to crowd density, which are known as sound waves in ordinary materials, as well as dangerous failure events which can lead to crushing. However, since human crowds are actively moving at all times, existing theories for static solids cannot be applied to them. This research will develop a new set of theoretical and computational tools to model failure in active matter crowds. A long-term goal of this work is to understand which types of crowd structures are more likely to lead to local crushing events, and to develop tools to predict and prevent such events.Finally, this project will contribute to the education and professional development of a broad pipeline of interdisciplinary scientists and engineers. It will support ongoing efforts to broaden the participation of under-represented groups, including women, in STEM fields through professional development programming, and support the PI to develop a new “active matter” module for upper-division undergraduate and graduate students in an interdisciplinary Physical Cell Biology class. TECHNICAL SUMMARYThis award supports theoretical research and education. The PI aims to develop a broad theoretical and computational framework for predicting the dynamics of unstable and active solids, by exploiting and extending previously developed methods that use vibrational modes to predict deformation in stable disordered materials. The first objective is to use a new computational method to quantify the localized deformations and normal modes of unstable disordered solids during an avalanche or catastrophic failure event. These data will be used to develop an analytic continuum model that predicts brittle and ductile failure and incorporates features of both elasto-plastic and shear transformation zone models. The second objective is to elucidate a nascent connection between sheared particulate matter and active self-propelled particles, using a new computational technique. The third objective is to create a stable active matter simulation, based on “point-of-interest” human crowds, and match it to a non-active simulation with an artificial external potential, as a tractable starting point for extending vibrational mode analysis directly to active systems. This will enable simulations that gradually tune away from the stable active solid in order to generate a theoretical framework that can make accurate predictions about density fluctuations in human crowds and other active matter systems.This project will advance knowledge by identifying new types of material behaviors that are possible for driven or active systems at very high densities. Unlike active gases or fluids, these high density unstable and active solids can transmit shear stresses, exhibit strongly anisotropic behavior, and likely store memories. Preliminary data suggests these new methods can be used to predict dynamics and behavior in active or unstable avalanching systems, which would represent a systematic approach to rationally design active solids to exhibit specified rheological behaviors or accomplish tasks. A second thrust will focus on a new idea for quantitatively comparing sheared particulate systems and active matter, in order to understand which ideas from well-studied sheared systems can be adapted to make prediction for active matter, and also where there are important differences between sheared and active systems that require new theories. Together, this will permit the development of an analytic continuum model for predicting avalanches and instabilities in both sheared and active matter systems.This work is applicable to problems of societal import. Avalanches and catastrophic brittle failure in granular materials and structural glasses are important in industry and nature – the tools developed here to constrain continuum models based on microscopic material properties could improve scientists’ ability to predict earthquake and landslide dynamics, as well as help rationally design better structural materials. This funding would also contribute to a societal goal of broadening participation in STEM, through training and mentoring of female scientists, including a systematic series of women-specific professional development events. As part of this proposal, the PI will also develop an active matter module, with lecture materials, active learning exercises, and a group research project that will be deployed in a course for upper-level undergraduate and graduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.