Departure from elasticity in granular layers: Investigation of a crossover overload force

Aiming at characterizing the departure from elasticity in granular materials. we study, by means of numerical molecular dynamics simulations, the stress response of a layer submitted to increasing overload forces. Comparing normalized stress profiles to a reference small overload case, similar to 0.1 (m)g, we compute root mean square (RMS) differences, averaged over several independent realizations, as a function of the overload force. The results indicate two different regimes for these RMS data: an elastic plateau at small overload values and an increase of the RMS at large forces. This increase is due to small (and frequent) as well as large (and rare) rearranging events. We show that one can extract from both of these contributions a crossover value for the overload force, which separates the two regimes. (c) 2009 Elsevier B.V. All rights reserved.