Abstract
Static granular packs have been studied in the last three decades in the frame of a modified equilibrium statistical mechanics that assumes ergodicity as a basic postulate. The canonical example on which this framework is tested consists in the series of static configurations visited by a granular column subjected to taps. By analyzing the response of a realistic model of grains, we demonstrate that volume and stress variables visit different regions of the phase space at low tap intensities in different realizations of the experiment. We show that the tap intensity beyond which sampling by tapping becomes ergodic coincides with the forcing necessary to break all particle-particle contacts during each tap. These results imply that the well-known "reversible" branch of tapped granular columns is only valid at relatively high tap intensities.Received: 2 November 2015, Accepted: 22 December 2015; Edited by: C. S. O'Hern; Reviewed by: A. Baule, Queen Mary University of London, UK.; DOI: http://dx.doi.org/10.4279/PIP.080001Cite as: P A Gago, D. Maza, L A Pugnaloni, Papers in Physics 8, 080001 (2016)This paper, by P A Gago, D. Maza, L A Pugnaloni, is licensed under the Creative Commons Attribution License 3.0.
Highlights
By analyzing the response of a realistic model of grains, we demonstrate that volume and stress variables visit different regions of the phase space at low tap intensities in different realizations of the experiment
Our analysis of the steady-states of tapped granular systems indicate that these states are historydependent for tap intensities below a certain threshold
This is in contradiction with the general assumption that macroscopic time averages —such as the volume fraction— can be recovered when the amplitude of the perturbation applied to the system is tuned back and forth
Summary
Edwards and Oakeshot introduced a tentative approach inspired by the ideas of equilibrium statistical mechanics to formally describe the global properties of a static
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