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：颗粒材料在日常生活中无处不在。 “粒状”不仅指盐、米或沙等坚硬的物体，也指坚硬的物体。还包括气泡等软物体以及细胞和行人等生物体。致密颗粒材料可能会发生堵塞、雪崩或突然凝固成无序“堵塞”结构的剧烈行为。 该研究项目提出了这样的问题：当颗粒与固定框架接触时，这些现象如何表现出来？在这项研究中，框架是一个由小型障碍物或“别针”组成的网格。 （在二维中，人们可能会想到弹球游戏中的销钉。）销钉会影响颗粒堆积中发生突然转变时的情况，以及形成的堵塞固体的结构和动力学。除了其理论意义之外，该项目还具有一些应用，例如利用障碍物来防止颗粒或人员的干扰；并制造更有弹性且体积更小的新卡塞材料。通过实验和计算机模拟研究了销钉对材料结构和动力学的影响。主要研究人员是四名教职人员，两所仅提供物理学本科学位的机构各有一名实验物理学家和一名计算物理学家。 他们的学生直接与教师合作，在理论丰富且实践性强的领域体验计算和/或实验研究。技术摘要：颗粒材料的填充，例如工业供应管线或生物体中的颗粒材料，在结构或流动行为方面表现出显着的变化，例如通道的突然重新排列、塌陷和突然堵塞。这种变化是由于几何挫败造成的，因为颗粒经历了堵塞和卡住的转变。变形和流动很大程度上取决于系统跨力网络，它在外力和扭矩、约束和内部颗粒相互作用之间进行折衷。虽然对致密颗粒物质有很多研究，但对颗粒系统流变学的研究却很少，其中包括让人想起限制的效应：系统内部局部钉扎位点形式的冻结自由度。该项目解决了关于应力和流场的空间相关性的关键、开放性问题，系统地研究了这些针的存在，无论是晶格还是无序阵列（因此，猝灭有序或无序）的形式如何影响结构和流动。主要研究人员的活动包括确定这种新颖的有序/无序转变的相图；计算弹性模量、局部应力场和表征受钉扎几何形状影响的力网络的参数； 使用粒子尺度跟踪来描述由于剪切下微观重排而产生的堆积结构和运动学；以及将这些见解扩展到活性颗粒物质的第一步。 这项工作需要通过两个主要本科机构的四名研究人员之间的合作进行数值模拟和实验。实验涉及使用光弹性颗粒二维组件的平面、简单和库埃特剪切。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力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