We investigate the two-dimensional packing of extremely prolate (aspect ratio L/D>10) granular materials, comparing experiments with Monte-Carlo simulations. In experimental piles of particles with aspect ratio 12 we find the average packing fraction to be 0.68 +/- 0.03. Both experimental and simulated piles contain a large number of horizontal particles, and particle alignment is quantified by an orientational order correlation function. In both simulation and experiment the correlation between particle orientation decays after a distance of two particle lengths. It is possible to identify voids in the pile with sizes ranging over two orders of magnitude. The experimental void distribution function is a power law with exponent -2.37 +/- 0.05. Void distributions in simulated piles do not decay as a power law, but do show a broad tail. We extend the simulation to investigate the scaling at very large aspect ratios. A geometric argument predicts the pile number density to scale as the aspect ratio to the -2 power. Simulations do indeed scale this way, but particle alignment complicates the picture, and the actual number densities are quite a bit larger than predicted.
Department, Program, or Center
School of Physics and Astronomy (COS)
K. Stokely, A. Diacou, and S. V. Franklin, Two-dimensional packing in prolate granular materials, Phys. Rev. E 67, 051302 (2003). https://doi.org/10.1103/PhysRevE.67.051302
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