Statistical Properties of Dense Granular Materials: Force Transmission, Jamming and Fluctuations

滑坡是粒状物质流动的一个例子，它可以给人们的生活造成严重破坏。该项目包括一系列精心设计的实验，以测试颗粒材料（如沙子、煤、金属矿石、药粉甚至狗粮）在受到机械力作用时的行为模型。尽管处理这些材料的财务成本很高，仅在美国每年就估计约为1万亿美元，但我们对这些材料流动的基本理解和预测能力远远落后于更传统的流体和固体。最近的理论工作指出了描述颗粒材料的令人兴奋的新方法。但这些模型必须通过仔细的实验测试来验证。该项目将进行精密实验，以测量颗粒系统中的力及其影响。它将专注于理解单个颗粒的行为如何在工业或家庭环境中控制颗粒系统的整体行为。这里的目标是开发新的方法来理解和预测颗粒行为，有可能影响当前的关键工业流程，提高其效率并降低相关成本。该项目将培养学生，并为就业行业和自然保护提供训练有素的劳动力。一个重要的目标是通过参与各级的研究项目，使代表性不足的少数民族参与进来。该个人研究者奖旨在通过关注三个关键问题来提供对致密颗粒材料的基本理解：1)颗粒固体中的力和力的传递，2)干扰，破坏和颗粒塑性的性质，以及3)新的统计原理的适用性，包括爱德华兹熵和波动耗散理论在实际颗粒系统中的应用。力传递和统计方面的工作将涉及二维光弹性方法，通过格林函数测量来测试最新的力传递模型。这些二维调查将通过使用高分辨率电容技术对力及其在三维中的传输进行研究来补充。对干扰附近颗粒统计行为的预测将进行实验测试。这些研究还将解决剪切颗粒材料的塑性破坏性质，并借鉴描述无序分子材料的最新理论进展。实验将通过表征一个特殊设计的颗粒系统的体积波动来测试爱德华兹熵的相关性，探索由扩散率和迁移率之比给出的扩展颗粒温度，并探索波动-耗散定理在剪切颗粒系统中的应用。长期目标是提高颗粒物料工业处理的可预测性，这对国民经济很重要。这套拟议的实验还将为研究生、本科生和高中生提供研究训练和机会，让他们参与到传统上在物理学领域代表性不足的群体中。

Non-Technical AbstractA landslide, which can play havoc with people's lives, is an example of flow of granular material. This project consists of a series of experiments that are carefully design to test models of how granular materials, such as sand, coal, metal ores, pharmaceutical powders, and even dog food, behave when subjected to mechanical forces. Despite the high financial cost of handling these materials, estimated to be about one trillion dollars a year in the US alone, our basic understanding and the ability to predict flow of these materials lags far behind that for more conventional fluids and solids. Recent theoretical work points towards exciting new ways of describing granular materials. But these models have to be validated by careful experimental tests. Precision experiments will be performed under this project to measure forces and their effect in granular systems. It will focus on understanding how the behavior of individual grains governs the bulk behavior of granular systems in industrial or domestic settings. The goal here is the development of new ways to understand and predict granular behavior, with the potential to impact the current key industrial processes and improve their efficiency and bring down the associated costs. This project will train students and contribute to highly trained workforce for jobs industries and nature preservation. An important goal will be to involve under-represented minorities through participation in research projects at all levels.Technical Abstract This individual investigator award is directed toward providing a basic understanding of dense granular materials by focusing on three key issues: 1) Forces and transmission of forces in granular solids, 2) the nature of jamming, failure and granular plasticity, and 3) the applicability of new statistical principles, including Edwards entropy and Fluctuation Dissipation theory to real granular systems. The work on force transmission and statistics will involve photoelastic methods in 2D to test very recent models of force transmission via Green's function measurements. These 2D investigations will be supplemented by studies of forces and their transmission in 3D using high-resolution capacitative techniques. Predictions for granular statistical behavior near jamming will be experimentally tested. These studies will also address the nature of plastic failure for sheared granular materials and draw on recent theoretical progress in describing disordered molecular materials. Experiments will test the relevance of Edwards entropy by characterizing volume fluctuations of a specially designed granular system, probe an extended granular temperature given by the ratio of diffusivity and mobility, and probe an application of the fluctuation-dissipation theorem to a sheared granular system. A long-term goal is to enhance the predictability for industrial handling of granular materials, which is important for the national economy. The suite of proposed experiments will also provide research training and opportunities for graduate, undergraduate and high-school students with involvement of groups traditionally under-represented in physics.