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Volume fluctuations and geometrical constraints in granular packs

Tomaso Aste
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Abstract

Structural organization and correlations are studied in very large packings of equally sized acrylic spheres, reconstructed in three-dimensions by means of X-ray computed tomography. A novel technique, devised to analyze correlations among more than two spheres, shows that the structural organization can be conveniently studied in terms of a space-filling packing of irregular tetrahedra. The study of the volume distribution of such tetrahedra reveals an exponential decay in the region of large volumes; a behavior that is in very good quantitative agreement with theoretical prediction. I argue that the system's structure can be described as constituted of two phases: 1) an `unconstrained' phase which freely shares the volume; 2) a `constrained' phase which assumes configurations accordingly with the geometrical constraints imposed by the condition of non-overlapping between spheres and mechanical stability. The granular system exploits heterogeneity maximizing freedom and entropy while constraining mechanical stability.

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Tomaso Aste. 2005-07-12. Volume fluctuations and geometrical constraints in granular packs. https://doi.org/10.1103/physrevlett.96.018002

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