Title: Random loose packings of frictional grains

Author (Invited): Narayanan Menon, University of Massachusetts Amherst

Abstract:

I will discuss experimental results on loose packings created by gentle deposition of monodisperse spheres in a fluid. The limiting volume fractions of these random loose-packed states depend on the interparticle friction. I will then discuss ongoing experiments in which we study the mechanical stability of the loose packings. The threshold of failure scales as a fractional power of the strain rate, indicating that the regime of linear response vanishes for quasi-static deformations of a packing that has been prepared within a finite time. The yield stress also increases with a similar slow power of the age of the packing. Both these responses are reported as a function of volume fraction, close to the random loose packing limit. The structural changes that accompany the plastic behaviour that follows failure are studied by 3-dimensional tomographic techniques.