Master curves for the stress tensor invariants in stationary states of static granular beds. Implications for the thermodynamic phase space

Abstract

We prepare static granular beds under gravity in different stationary states by tapping the system with pulsed excitations of controlled amplitude and duration. The macroscopic state---defined by the ensemble of static configurations explored by the system tap after tap---for a given tap intensity and duration is studied in terms of volume, , and force moment tensor, . In a previous paper [Pugnaloni et al., Phys. Rev. E  82, 050301(R) (2010)], we reported evidence supporting that such macroscopic states cannot be fully described by using only or , apart from the number of particles . In this work, we present an analysis of the fluctuations of these variables that indicates that and may be sufficient to define the macroscopic states. Moreover, we show that only one of the invariants of is necessary, since each component of falls onto a master curve when plotted as a function of . This  implies that these granular assemblies have a common shape for the stress tensor, even though it does not correspond to the hydrostatic type. Although most results are obtained by molecular dynamics simulations, we present supporting experimental results. Received:  11 May 2011,  Accepted:  15 July 2011;  Edited by:  J-C. Geminard;  Reviewed by:  B. Tighe, Instituut-Lorentz, Universiteit Leiden, Netherlands;  DOI: http://dx.doi.org/10.4279/PIP.030004 Cite as: L. A. Pugnaloni, J. Damas, I. Zuriguel, D. Maza, Papers in Physics 3, 030004 (2011)