Abstract:
A granular system is de ned as a large collection of macroscopic grains (linear
dimensions greater than 1 m) of solid matter, with thermal
uctuations
being irrelevant. Some examples of granular matter are sand, rice, co ee,
salt, etc. This kind of matter is very important in industry. The second
most manufactured class of materials are in the form of granular matter [2].
Granular materials can
ow like a liquid (like sand in an hourglass), resist
deformation like a solid (like the sand under feet at the beach), or quickly
transition between these states (like pebbles in a rockslide). Granular materials
have properties that have no equivalent in regular materials like wood,
metal, or rubber. In solids like these a force applied to the surface propagates
through the material smoothly and predictably. If a uniform force is applied
to the surface of a material, every equally sized cross-section of that material
bears the same amount of load. In granular materials, however, the situation
is very di erent: in a sand pile under stress (that is, when a force is applied
to its surface), the force is distributed unevenly { some individual sand grains
bear far more load than others. Surprisingly, this remains true even when the
sand grains themselves are identical. Whats more, the load-bearing grains
connect to one another to make a fractal, lightning-like pattern inside the material, like that shown in Figure 1.1 [1]. These string-like arrangements of
load-bearing grains are called force chains.
