Collaborative Research: RUI: Jammed granular matter within networks of pins: Structure, elasticity, plasticity and rheology under shear

合作研究：RUI：针网络中堵塞的颗粒物质：剪切下的结构、弹性、塑性和流变学

• 批准号: 1905474
• 负责人: Amy Graves
• 金额: $ 31.02万
• 依托单位: Swarthmore College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-12-01 至 2024-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1905474&HistoricalAwards=false
• 关键词: Collaborative; Research; RUI; Jammed; granular

Nontechnical Abstract:Granular Materials are ubiquitous in daily life. By “granular” one means not only hard objects like salt, rice, or sand; but also soft objects like bubbles, and living entities like cells and pedestrians. Dense granular materials can behave dramatically by clogging, avalanching, or suddenly solidifying into a disordered “jammed” structure. This research project asks the question: How do these phenomena manifest themselves when the grains are in contact with a fixed framework? In this research, the framework is a lattice of diminutive obstacles, or “pins”. (In two dimensions, one might think of the pins in a Pachinko game.) Pins influence both when a sudden transition occurs in a granular packing, and the structure and dynamics of the jammed solid which forms. Beyond its theoretical interest, this project has applications like utilizing obstacles for the prevention of jamming of particles or people; and making new jammed materials which are more elastic and less bulky. The influence of pins on the material’s structure and dynamics is studied both with experiments as well as computer simulations. The principal investigators are four faculty members, with an experimental and a computational physicist at each one of two institutions which offer only undergraduate degrees in physics. Their students work directly with faculty to experience computational and/or experimental research in a field that is both theory-rich and highly practical. Technical Abstract:Packings of granular materials, as for example in industrial supply lines or in living organisms, exhibit striking changes in structural or flowing behavior such as abrupt rearrangements, collapses and sudden blockading of channels. Such changes are due to geometrical frustration, as grains experience clogging and jamming transitions. Deformation and flow are largely determined by system-spanning force networks, which broker a compromise between external forces and torques, confinement, and internal granular interactions. While there have been many studies of dense granular matter, there have been few on the rheology of granular systems which include an effect reminiscent of confinement: frozen degrees of freedom in the form of localized pinning sites internal to the system. This project, which addresses critical, open questions on spatial correlations of stress and flow fields, is a systematic study of how the presence of such pins, either in the form of a lattice or a disordered array (hence, quenched order or disorder) influences structure and flow. Activities of the principal investigators include determining the phase diagram for this novel order/disorder transition; calculating elastic moduli, local stress fields and parameters characterizing the force network as influenced by pinning geometry; use of particle-scale tracking to describe packing structure and kinematics due to microscopic rearrangements under shear; and first steps toward extending these insights to active granular matter. The work entails both numerical simulation and experiments through a collaboration between four investigators at two primarily undergraduate institutions. Experiments involve planar, simple, and Couette shear using two-dimensional assemblies of photoelastic grains.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.

非技术摘要：粒状材料在日常生活中无处不在。通过“颗粒状”，不仅意味着盐，大米或沙子等硬物体；而且还有诸如气泡和牢房和行人之类的生物实体之类的柔软物体。浓密的颗粒材料可以通过堵塞，雪崩或突然凝固成无序的“卡住”结构来表现出色。该研究项目提出了一个问题：当谷物与固定框架接触时，这些现象如何表现出来？在这项研究中，该框架是小小的障碍物或“销钉”的晶格。 （在两个维度上，一个人可能会想到pachinko游戏中的销钉。）当突然过渡发生在颗粒堆中，以及形成堵塞的固体的结构和动力学时，销钉都会影响。除了其理论上的兴趣之外，该项目还具有诸如使用障碍来预防颗粒或人的障碍。并制作新的堵塞材料，这些材料更具弹性和笨重。通过实验和计算机模拟研究了引脚对材料结构和动力学的影响。首席研究人员是四名教职员工，在两个机构中的每个机构中的每个机构中的每一个都有实验性和一名计算物理学家，仅提供物理学的本科学位。他们的学生直接与教师合作，在理论丰富且高度实用的领域中体验计算和/或实验研究。技术摘要：颗粒状材料的包装，例如工业供应线或生活组织中，揭示了结构性或流动行为的惊人变化，例如突然重排，崩溃和突然阻止通道。这种变化是由于几何挫败感引起的，因为谷物经历了堵塞和干扰过渡。变形和流动在很大程度上取决于系统跨力的力网络，该网络会在外部力和扭矩，限制和内部颗粒状相互作用之间妥协。虽然有许多关于颗粒状稠密物质的研究，但颗粒系统的流变学很少，其中包括限制的效果：以局部固定位点的形式冷冻自由度。该项目解决了有关压力和流场的空间相关性的关键问题，是对这种销钉的存在（以晶格或无序阵列的形式（因此，猝灭的顺序或混乱）的形式）的系统研究。主要研究人员的活动包括确定这种新秩序/疾病过渡的相图；计算弹性模量，局部应力场和参数，这些参数表征了由固定几何形状影响的力网络；使用粒子尺度跟踪来描述由于剪切下的微观重排而引起的堆积结构和运动学；以及将这些见解扩展到主动粒状物质的第一步。这项工作需要通过两个主要本科机构的四个投资者之间的合作来进行数值模拟和实验。实验涉及平面，简单和COUETTE剪切，使用光弹性晶粒的二维组件。该奖项反映了NSF的法定任务，并且使用基金会的知识分子优点和更广泛的影响审查标准，被认为值得通过评估来获得支持。

项目成果

Gender Disparities in Pandemic Productivity

流行病生产力中的性别差异

• 发表时间: 2021
• 期刊: CSWP COM gazette
• 作者: Malish, J.L;Graves, A.L.
• 通讯作者: Graves, A.L.

Jammed solids with pins: Thresholds, force networks, and elasticity

用销钉卡住的固体：阈值、力网络和弹性

• DOI: 10.1103/physreve.106.034902
• 发表时间: 2022
• 期刊: Physical Review E
• 影响因子: 2.4
• 作者: Zhang, Andy L.;Ridout, Sean A.;Parts, Celia;Sachdeva, Aarushi;Bester, Cacey S.;Vollmayr-Lee, Katharina;Utter, Brian C.;Brzinski, Ted;Graves, Amy L.
• 通讯作者: Graves, Amy L.

Melting the Glass Ceiling in Physics

融化物理学的玻璃天花板

• 发表时间: 2022
• 期刊: CSWP COM gazette
• 作者: Amy L. Graves