A 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.
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.
