Granular media -- including familiar systems such as sand, soil, rice, glass beads -- are, ironically, considered singularly unusual by many physicists: They violate energy conservation, thermodynamics, the fluctuation-dissipation theorem, the Onsager relation and more general principles. They are, in one word, athermal.
In this talk, it will be argued that, properly viewed, granular media are quite normal and thermal. The usual tools of theoretical physics are therefore applicable and useful, and have been employed to derive a set of partial differential equations -- GSH (for granular solid hydrodynamics) -- by appropriately generalizing the Navier-Stokes equations. The result is capable of accounting for a wide range of granular phenomena, including
- static stress distribution,
- elasto-plastic motion, especially the critical state,
- the μ(I)- and Kamrin's nonlocal-rheology,
- shear band, compaction, sound propagation, ...