Abstract
Random packings of non-spherical granular particles are simulated by combining mechanical contraction and molecular dynamics, to determine contact numbers as a function of density. Particle shapes are varied from spheres to thin rods. The observed contact numbers (and packing densities) agree well with experiments on granular packings. Contact numbers are also compared to caging numbers calculated for sphero-cylinders with arbitrary aspect-ratio. The caging number for rods arrested by uncorrelated point contacts asymptotes towards \({\langle \gamma \rangle = 9}\) at high aspect ratio, strikingly close to the experimental contact number \({\langle C \rangle \approx 9.8}\) for thin rods. These and other findings confirm that thin-rod packings are dominated by local arrest in the form of truly random neighbor cages. The ideal packing law derived for random rod–rod contacts, supplemented with a calculation for the average contact number, explains both absolute value and aspect-ratio dependence of the packing density of randomly oriented thin rods.
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Acknowledgments
We are grateful to Stephen Williams for valuable discussions and Thijs Vlugt for his great help with setting up computational facilities. This work is part of the Granular Matter programme of the Stichting voor Fundamenteel Onderzoek der Materie (FOM), financially supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO).
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Open Access This is an open access article distributed under the terms of the Creative Commons Attribution Noncommercial License (https://creativecommons.org/licenses/by-nc/2.0), which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.
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Wouterse, A., Luding, S. & Philipse, A.P. On contact numbers in random rod packings. Granular Matter 11, 169–177 (2009). https://doi.org/10.1007/s10035-009-0126-6
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DOI: https://doi.org/10.1007/s10035-009-0126-6