Title: Random to ordered dense granular packings

Author (Talk): Katha Reddy, Clark University, Physics department

Abstract:

We characterize the structure of densely packed frictional granular spheres cyclically sheared between parallel walls under constant pressure boundary conditions with a fluorescent refractive index matched liquid imaging technique. This technique allows us to measure the three dimensional particles position and obtain the Voronoi tessellation corresponding to the particles in the bulk. We calculate the radial distribution function, g(r) from the measured position and show that its significant features can be captured by the Percus-Yevick formula derived for frictionless random packed spheres for initial volume fraction $\Phi $ = 0.59{\$}. However, experimental g(r) for volume fractions > 0.61 deviates significantly from P-Y equation as the former shows peaks corresponding to an ordered structure .The angular correlation of the particles as measured by the bond order metric, Q$_{6}$ increases from 0.33 (random , volume fraction = 0.595) to 0.41 (partially ordered, volume fraction = 0.655 ) over the range of cycle numbers investigated. It has been observed that Voronoi free volumes deviate from gamma distributions postulated for frictionless spheres for the entire range of volume fractions in the experiment .Though some of these measures show similarity of the observed granular packing compared with random packing of frictionless spheres for volume fractions upto 0.61 , they are different for $\Phi $ > 0.61{\$}.