Geometry and Mechanics of Nonthermal Packings

* 技术摘要 * 所提出的实验旨在同一基础上探测（a）致密颗粒、（B）延伸的一维细丝和（c）二维薄片的组装体的结构、线性响应和失效。 由于这些填充物中的元素是宏观的，所以填充物是非热的，因此远离平衡。该奖项有助于了解非目标包装协议是否会导致具有统计可重复特性的最终状态。 拟议的实验将研究每种类型的模型系统的三维结构。同时，将施加剪切力和压缩力以探测材料的机械强度。同时，将施加小载荷以消除线性响应。 赋予材料刚性的空间单元通常通过研究材料在外部载荷下如何破坏而最清楚地暴露出来，因此也将施加足够大的载荷以产生屈服。拟议的工作使研究生和本科生接触到各种技术，并有机会在新兴的物理领域工作。PI也是在马萨诸塞大学阿默斯特分校为软物质物理学的早期职业研究生举办的年度暑期学校的组织者。非技术摘要 * 大颗粒集合体的机械性质和结构比分子或原子集合体的机械性质和结构知之甚少。拟议的工作将研究这些系统的三个几何上不同的类别：（1）颗粒材料，范围从药物粉末到矿物矿石，从粮食到它们生长的土壤。(2)纤维材料是植物物质的主要成分，也是从纸到织物和绝缘材料等人类产品的主要成分。 (3)褶皱的床单出现在花和叶，以及在垃圾压实和减震。 我们的目标是通过三维成像技术研究这些系统的理想化版本，该技术允许在对材料施加力的同时可视化结构。这将为这些材料中负责其机械性能的结构元素提供重要线索。拟议的工作使研究生和本科生接触到各种技术，并有机会在新兴的物理领域工作。PI也是在马萨诸塞大学阿默斯特分校举办的年度暑期学校的组织者，为软物质和统计物理学的早期职业研究生举办。

****Technical Abstract****The proposed experiments are designed to probe on the same footing, the structure, linear response and failure of assemblies of (a) compact grains, (b) extended one-dimensional filaments, and (c) two-dimensional sheets. Since the elements in these packings are macroscopic, the packings are nonthermal, and are therefore far from equilibrium. The award contributes to understanding whether untargeted packing protocols lead to final states with statistically reproducible properties. The proposed experiments will study the three-dimensional structure of model systems of each type. At the same time, forces of shear and compression will be applied to probe the mechanical strength of the material. Simultaneously, small loads will be applied to characterise the linear response. The spatial elements that bestow rigidity on a material are often most clearly exposed by studying how the material fails under external loading, so loads large enough to generate yielding will also be imposed. The proposed work gives graduate and undergraduate students exposure to a variety of techniques and the opportunity to work in newly-emerging areas of physics. The PI is also an organizer of an annual summer school hosted at UMass Amherst for early-career graduate students in soft matter physics.****Non-Technical Abstract****The mechanical properties and structure of assemblies of large particles are much more poorly understood than that of assemblies of molecules or atoms. The proposed work will study three geometrically different classes of these systems: (1) Granular materials which range from range from pharmaceutical powders to mineral ores, and from food grains to the soils they grow in. (2) Fibrous materials are the main constituent of plant matter, as well of human products ranging from paper to fabrics and insulants. (3) Crumpled sheets appear in flowers and leaves, as well as in trash compaction and shock absorption. The goal is to study idealized versions of these systems by 3-dimensional imaging techniques that allow the structure to be visualized while forces are applied to the material. This will give important clues as to the structural elements in these materials that are responsible for their mechanical properties. The proposed work gives graduate and undergraduate students exposure to a variety of techniques and the opportunity to work in newly-emerging areas of physics. The PI is also an organizer of an annual summer school hosted at UMass Amherst for early-career graduate students in soft matter and statistical physics.