Granular Packings

This experiment was performed by: Luis A. Pugnaloni, Iván Sánchez, Paula A. Gago, José Damas, Iker Zuriguel, and Diego Maza.

arXiv

Some years ago the Chicago group development a 3D experimental setup [1] to study the density of a vibrated granular media as a function of time (Taps). They Found that the behavior of this density decay in a monotonous way and the existence of steady states and how they reached by tapping regimen. This experimental results confirm the previous theory propose by Edwards and Oakshott [2] about the thermodynamic description. However, very recent computational simulations [3,4] show that the behavior of packing fraction (density) is non-monotonous for large amplitude

of tap, according with this is possible to find two configuration with the same packing fraction but reaching (the steady state) with a different tapping regimen, this imply that another variable is necessary to distinguish this two configurations. Because of this is very important understanding the real behavior of packing fraction. This work is on 2D case showing a few results of 3D case

Objetive

We analyze, experimentally, the steady states, obtaine

d by tapping, of a 2D granular layer. Contrary to the usual assumption, we show that the density–acceleration curve is nonmonotonous. In consequence some steady states have the same mean volume but be reached by tapping the system with very different intensities.

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We found that reached the steady states is short time of tapping for the 2D granular layer different for the 3D case (not included on this poster).

We found that the packing fraction in a granular layer is not monotonous and the fluctuations is different at Both sides of minimum. This two curves appears to be the general behavior for different times (frequency) of tapping regimen.

From the experimental results we confirm the existence of two different states with the same packing fraction obtained by using different values for the excitation parameter G, from this we concluded that another variable is necessary for the thermodynamic description (see poster: Static granular packings: The relevant state variables by Paula Gago).

Jose Damas

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