• Systèmes complexes et transition énergétique › Physique statistique et systèmes complexes

• UMR 3680 - Service de Physique de l'Etat Condensé (SPEC) • UMR 3680 - Laboratory of Condensed Matter Physics (SPEC)

• SPHYNX

Granular matter : Relaxation and response to a localized perturbation

Olivier Dauchot

Mobile volume fraction evolution for two different realizations at similar pile slope : (o) q=15°; (+) q=16.5°. Inset is the log-lin plot of the same data.

First, the micro-displacements generated by a small localized overload at the free surface are visualized experimentally inside a packing of steel beads. For a triangular packing, beads rearrangements remain confined in two inverted triangles on both sides of the applied overload. This pattern disappears for stronger disorder. A simple model allows us to account for these observations and to relate them to the stress function response measured via photoelastic visualizations.

Perturbation experiments have allowed us to confirm the emergence of strong spatial correlations when increasing the pile slope, which are reminiscent of the clusters that we observed in flows. Finally we have extracted in the unperturbed case a two-time relaxation function, which can be shown to rescale in an aging like manner with a `reparametrization' of time suggested by a simple model that we introduce in order to describe our experimental data. Moreover, this model allows to relate the above relaxation function to a two-time correlation function which shares strong similarities with auto-correlation functions appearing in aging systems.

#981 - Màj : 02/02/2008