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Micro‐inertia origin of instabilities in granular materials
Authors:Antoine Wautier  Stephane Bonelli  François Nicot
Institution:1. AgroParisTech‐ENGREF, 75732 Paris, France;2. Irstea UR RECOVER, 13182 Aix‐en‐Provence Cedex 5, France;3. Université Grenoble Alpes, Irstea, UR ETGR, F‐38402 St‐Martin‐d'Hères, France
Abstract:Within the framework of the second‐order work theory, the onset of instabilities is explored numerically in loose granular materials through three‐dimensional DEM simulations. Stress controlled directional analysis are performed in Rendulic's plane, and a particular attention is paid to transient evolutions at the microscale. Thanks to a micromechanical analysis, the onset and development of transient mechanical instabilities is explored. It is shown that these instabilities result from the unjamming and bending of a few force chains associated with a local burst of kinetic energy. This burst of kinetic energy propagates to the whole sample and provokes a generalized unjamming of force chains. As force chains buckle, a phase transition from a quasi‐static to an inertial regime is observed. At the macroscopic scale, this results in a transient softening and a loss of controllability. After the collapse of existing force chains, the development of plastic strain is eventually stopped as new stable force chains are built.
Keywords:bending  force chain  granular material  second‐order work  stability and bifurcation  unjamming
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