From rice to snow

Abstract

[This address was presented by Pierre-Gilles de Gennes as the Nishina Memorial Lecture at the University of Tokyo, on April 3, 1998.] We present here some general features of granular materials, of their importance, and of the conceptual difficulties which they exhibit. For static problems, we insist on the difference between textures, which represent frozen correlations between grains, and stress tensors. We argue that in systems like heaps and silos, texture is present, but the main features of the stress distribution do not depend on it, and a description using an isotropic medium is a good starting point. We also discuss avalanche flows, using a modified version of the equations of Bouchaud et al, which might be valid for thick avalanches. © Nishina Memorial Foundation 2008.