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

滑坡是颗粒物质流动的一个例子，它会给人们的生活带来严重的破坏。该项目包括一系列精心设计的实验，以测试颗粒状材料（如沙子，煤炭，金属矿石，药物粉末，甚至狗粮）在受到机械力时的行为。 尽管处理这些材料的财务成本很高，仅在美国估计每年约为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。 最近的理论工作指向令人兴奋的新方法来描述颗粒材料。但是这些模型必须通过仔细的实验测试来验证。本项目将进行精密实验，以测量颗粒系统中的力及其影响。它将侧重于了解如何在工业或家庭环境中的单个颗粒的行为支配颗粒系统的整体行为。我们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过程，提高其效率并降低相关成本。该项目将培训学生，并为就业、工业和自然保护提供训练有素的劳动力。 一个重要的目标将是通过参与各级研究项目，让代表性不足的少数民族参与进来。技术摘要该个人研究者奖旨在通过关注三个关键问题，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）堵塞、破坏和颗粒塑性的性质，3）新的统计原理，包括Edwards熵和涨落耗散理论对真实的颗粒系统的适用性。关于力传递和统计的工作将涉及2D光弹性方法，以通过绿色函数测量来测试力传递的最新模型。这些2D调查将通过使用高分辨率容量技术的3D力及其传输研究来补充。将通过实验测试对干扰附近的粒度统计行为的预测。这些研究还将解决剪切颗粒材料的塑性破坏的性质，并利用最近在描述无序分子材料的理论进展。实验将测试爱德华熵的相关性通过表征体积波动的一个专门设计的颗粒系统，探测扩展的颗粒温度的扩散率和流动性的比率，并探测应用的波动耗散定理剪切颗粒系统。 长期目标是提高颗粒物料工业处理的可预测性，这对国民经济至关重要。这套拟议的实验还将为研究生、本科生和高中生提供研究培训和机会，让传统上在物理学中代表性不足的群体参与进来。

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.