July 9, 1994
Avalanche in a pile of mustard seeds
The University of Chicago Materials Center has initiated an extensive effort to study granular materials. These materials have great industrial importance. In addition, granular systems reveal many properties that are not intuitively simple and which do not have obvious explanations. A221 granular materials cut across the boundaries dividing gases, liquids and solids. A mass of sand forms a heap with non-horizontal top surfaces and in this way act like a solid. However, if the slope becomes too great, the pile will flow like a fluid. In sound propagation, they have behaviors different from both liquids and solids.
Sand has distinctive properties which are not found in other media: arching, variable density, dilatancy, and vibration-induced convection and size separation.
Fundamental questions exist: How does one characterize the randomness that exists in a pile and what variables control the degree of randomness? What characterizes the mechanical excitations that permit a system to relax and what controls the transmission of stress from static to strongly flowing states?
Description from the Materials Center Proposal from 1992.
Further Information: H. M. Jaeger and Sidney R. Nagel, "Physics of the Granular State", Science 255, 1523 (1992); H. M. Jaeger, J. B. Knight, C.-h. Liu, and S. R. Nagel, "What is shaking in the sand box?", Mat. Res. Soc. Bull. 19 (5), 25 (1994).