Onset of Mechanical Stability in Random Packings of Frictional Spheres

摘要

Using sedimentation to obtain precisely controlled packings of noncohesive spheres, we find that the volume fraction ϕRLP of the loosest mechanically stable packing is in an operational sense well defined by a limit process. This random loose packing volume fraction decreases with decreasing pressure p and increasing interparticle friction coefficient μ. Using x-ray tomography to correct for a container boundary effect that depends on particle size, we find for rough particles in the limit p→0 a new lower bound, ϕRLP=0.550±0.001.