Onset of mechanical stability in random packings of frictional spheres
Using sedimentation to obtain precisely controlled packings of noncohesive spheres, we find that the volume fraction $ϕ_{\rm RLP}$ 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 $p \to 0$ a new lower bound, $ϕ_{\rm RLP} = 0.550 \pm 0.001$.
cond-mat.soft↗