Incollection,
Generalized isostaticity and local structure of jammed packings of frictional grains
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)
Abstract
We show that in slowly generated two-dimensional packings of frictional spheres, a significant fraction of the friction forces lie at the Coulomb threshold - for small pressure $p$ and friction coefficient $\mu$, about half of the contacts. Interpreting these contacts as constrained leads to a generalized concept of isostaticity, which relates the maximal fraction of fully mobilized contacts and contact number. For $p0$, our frictional packings approximately satisfy this relation over the full range of $\mu$. In addition, several quantities, related to the local contact number, scale with $p$ and $\mu$, which allows to construct nontrivial structural invariants. Simple mean field arguments provide an explanation of the observed local structure, and give an estimate of an upper bound of the configurational entropy at the onset of jamming.
