Shear Jamming, Diffusion, Reversibility, Anisotropy, and Fluctuations in Dense Granular Materials

* 技术摘要 * 该项目涉及新颖的实验，以了解颗粒材料在堵塞附近的动态，静态和统计特性。 这些材料具有重要的技术意义，但其性质仍然知之甚少。 杜克小组和布兰代斯的合作者最近表明，摩擦颗粒系统的近堵塞特性比以前认为的要丰富得多，并表现出有序-无序转变，剪切堵塞，涉及复杂的接触和力网络。 该项目探讨了这些网络，其形成所涉及的物理过程，以及这些网络和过程对静态和动态颗粒特性的影响。 采用新型光弹性和激光扫描技术的二维和三维实验将解决以下几个问题：1）剪切堵塞附近颗粒材料的结构和力学特性及其对应变的动态响应; 2）剪切堵塞中摩擦的作用; 3）堵塞附近状态的良好统计特性所需的变量; 4）颗粒动力学、扩散运动和（剪切）堵塞附近的时间尺度; 5）颗粒材料的堵塞附近的流变响应; 6）3D与2D颗粒系统的结构和响应的差异。 博士后、博士学生和本科生将积极参与研究的各个阶段。PI，博士后和学生将积极参与小学和中学的外展活动。非技术摘要沙子，谷物，盐和药丸是一种特殊类型的物质，颗粒状材料的常见例子。 除了作为日常生活的一部分，颗粒材料，如煤，粮食，塑料原料，以及许多其他，形成了我们的经济的很大一部分。它们的特性既迷人又鲜为人知。在适当的条件下，它们像流体一样流动，但它们也可以变成固体并支撑重量。 类流体到类固体的转变对于实际应用特别重要，这是本项目的重点，该项目侧重于基本问题。 固体颗粒状态由颗粒间接触网络控制。 在最近的工作中，PI和Brandeis的合作者表明，这些控制流体-固体干扰过渡的网络具有比以前认为的更丰富和更新颖的特性。 该项目旨在了解导致网络形成的机制，以及这些机制对流体和固体颗粒状态的影响。 该项目整合了各级培训。 博士学生和博士后通过领导研究项目学习。 本科生和高中生通常通过相关项目参与。 PI，博士学生和博士后积极参与涉及中小学生的外联活动。 PI还通过与颗粒材料工业用户的互动积极参与技术转让，例如通过国际细颗粒研究所。

****Technical Abstract****This project involves novel experiments to understand the dynamical, static and statistical properties of granular materials near jamming. These materials are of great technical importance, yet their properties remain poorly understood. The Duke group and collaborators at Brandeis, recently showed that near-jamming properties of frictional granular systems are much richer than previously thought, and exhibit an order-disorder transition, shear jamming, involving complex networks of contacts and forces. This project explores these networks, the physical processes involved in their formation, and the impact that these networks and processes have on static and dynamical granular properties. Experiments in two and three dimensions, using novel photoelastic and laser scanning techniques, will address several issues: 1) structural and mechanical properties of granular materials near shear jamming and their dynamical response to strain; 2) the role of friction in shear jamming; 3) variables needed for a good statistical characterization of states near jamming; 4) particle dynamics, diffusive motion, and time scales near (shear) jamming; 5) near-jamming rheological response of granular material; 6) differentiation in the structure and response of 3D vs. 2D granular systems. Post-docs, Ph.D. students and undergraduates will be actively involved at all stages of research. The PI, post-docs and students will be actively involved in outreach to elementary and middle schools.****Non-Technical Abstract****Sand, cereal, salt, and pills are commonplace examples of a special type of matter, granular materials. Besides being part of daily life, granular materials, e.g. coal, grain, plastic feed stock, among many others, form a large part of our economy. They have properties that are both fascinating and poorly understood. Under the right conditions, they flow like a fluid, but they also can become solid and support weight. The fluid-like to solid-like transition is particularly important for practical applications, and it is the focus of the present project which focuses on fundamental questions. The solid granular state is controlled by networks of inter-grain contacts. In recent work, the PI and collaborators at Brandeis showed that these networks, which control the fluid-solid jamming transition, have much richer and more novel properties than was previously thought. This project seeks to understand the mechanisms leading to the formation of the networks, and the impact that these mechanisms have on both fluid and solid granular states. This project integrates training at all levels. Ph.D. students and post-docs learn by leading research projects. Undergraduate and high school students routinely participate via related projects. The PI, Ph.D. students and post-docs are actively involved in outreach involving elementary and middle school students. The PI is also actively involved with technology transfer through interactions with industrial users of granular materials, for instance through the International Fine Particle Research Institute.