Experiments on Granular Materials and Crumpled Sheets

University Of Massachusetts Amherst, Amherst MA

Investigators

Abstract

Non-technical This project seeks to extend our understanding of systems that are far from being in equilibrium. The experiments focus on two ubiquitous examples of such systems: granular media and crumpled elastic sheets. Granular media, such as sand or powders, are made up of a large number of individual grains. Likewise, a crumpled sheet (of paper, for example) is made up of flat facets delimited by creases. We seek to understand the properties of each of the constituent grains and how the properties of a large collection of them (grains, ridges in paper) are determined. For example, we will study how the network of ridges in a crumpled sheet confers rigidity on an otherwise floppy system. We will study how a large collection of sand grains can, under some conditions, pack into a solid form and flow like a liquid under other conditions. Undergraduate students from Univ. of Massachusetts, Amherst and other colleges in the area, will play a crucial role in exploratory work on new projects. Graduate students will gain exposure to a wide variety of experimental techniques. Furthermore, the subject materials are also industrially important and will give the students access to important applied problems. Technical: This project involves experimental studies of two archetypal non-equilibrium systems - granular media and crumpled elastic sheets. Granular media are made up of grains that interact by dissipative contact interactions. A crumpled sheet is made up of facets delimited by creases, both of which are nonlinear, localized elastic elements. In both systems the constituent elements are macroscopic, and therefore are not subject to thermal fluctuations. The research seeks to identify general principles governing phase behavior, fluctuations, bulk response and structure of such far-from-equilibrium systems. To this end, fluctuations are experimentally probed, related to measured linear response, and ordered and disordered arrangements of particles are characterized. Undergraduate students from the Univ. of Massachusetts, Amherst and other colleges in the area will play a crucial role in the exploratory work on new projects. Graduate students will gain exposure to many techniques - including high-speed video imaging, confocal microscopy, diffusive light scattering, acoustic and mechanical response techniques, and surface speckle interferometry. The materials to be studied are also industrially important and will give the students access to important applied problems.