A unified theory for granular matter

Developing a unified theory to describe granular matter, which can behave like either solid or fluid, is one of the grand challenges in modern science. This is mainly because the current theories, rooted in different origins, interpret granular matter from disparate perspectives and are hard to merge. In this work, we demonstrate that it is possible to generate such a generic theory by bridging the elastoplastic theory of solids with the rheological law of granular flow. The proposed theory or mathematical model can well explain the avalanching behaviours occurring in solid-fluid phase transition, and other related concepts such as interparticle interlocking, dilatancy, hysteresis, scaling law, and flow regimes in describing granular matter. Its applicability is tested in a variety of granular systems where solid- and fluid-like states coexist. This work therefore offers a simple but general theory to describe granular matter in a unified way.