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.

摘要：颗粒材料在日常生活中无处不在。这里的“颗粒”不仅指像盐、大米或沙子这样的坚硬物体；还有像气泡这样的柔软物体，以及像细胞和行人这样的生命体。致密的颗粒状材料可能会发生堵塞、雪崩或突然凝固成无序的“堵塞”结构。这个研究项目提出了一个问题：当颗粒与固定框架接触时，这些现象是如何表现出来的？在这项研究中，框架是一个由小障碍物或“针”组成的晶格。（在二维空间中，人们可能会想到柏青哥游戏中的球瓶。）销既影响颗粒填料中突然转变的发生，也影响形成的堵塞固体的结构和动力学。除了理论上的兴趣，这个项目还有一些应用，比如利用障碍物来防止粒子或人的干扰；并制造出更有弹性、体积更小的新型堵塞材料。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。主要研究人员是四名教职员工，分别有一名实验物理学家和一名计算物理学家，他们来自两所只提供物理学本科学位的机构。他们的学生直接与教师一起工作，在理论丰富和高度实用的领域体验计算和/或实验研究。技术摘要：颗粒物料的填料，例如在工业供应线或生物体中，在结构或流动行为上表现出显著的变化，如突然的重排、崩塌和通道的突然阻塞。这种变化是由于几何挫折，如颗粒经历堵塞和堵塞过渡。变形和流动在很大程度上取决于系统跨越的力网络，它调解了外力和扭矩、约束和内部颗粒相互作用之间的妥协。虽然对致密颗粒物质进行了许多研究，但很少有关于颗粒系统流变学的研究，其中包括一种让人想起约束的效应：以系统内部局部钉住位点的形式冻结的自由度。该项目解决了关于应力和流场空间相关性的关键开放问题，是对这些引脚的存在如何以晶格或无序阵列的形式（因此，淬火有序或无序）影响结构和流动的系统研究。主要研究人员的活动包括确定这种新型有序/无序转变的相图；计算弹性模量、局部应力场和受钉钉几何形状影响的力网特征参数；利用粒子尺度跟踪来描述由于剪切作用下微观重排引起的堆积结构和运动学；这是将这些见解扩展到活跃颗粒物质的第一步。这项工作包括数值模拟和实验，由两所主要本科院校的四名研究人员合作完成。实验包括平面剪切、简单剪切和使用二维光弹性颗粒组合的库埃特剪切。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。

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