Predictability and granular materials

Granular materials present a number of challenges to predictability The cla ssical description of a dense granular material is based on Coulomb frictio n. For a static array of grains, the Coulomb friction forces are typically underdetermined. If we are to make useful statements about such arrays, we must develop new approaches, including the development of statistical descr iptions. Granular materials also show large fluctuations in the local force s. These fluctuations are quite sensitive to small perturbations in the pac king geometry of the grains. In the past, they have typically been ignored. However, recent experiments and models are beginning to shed new light on their characteristics. This article briefly reviews some of this new work, and in particular presents experimental results characterizing fluctuations and the role of friction in granular materials. (C) 1999 Elsevier Science B.V. All rights reserved.