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DY: Fachverband Dynamik und Statistische Physik
DY 24: Granular matter II
DY 24.6: Talk
Thursday, February 28, 2008, 11:15–11:30, MA 004
Wet granulates under shear — •Seyed Habibollah Ebrahimnazhad, Martin Brinkmann, Jürgen Vollmer, and Stephan Herminghaus — MPI for Dynamics and Self-Organization, 37073 Göttingen
Small amounts of a wetting liquid render sand a stiff and moldable material. Cohesion between wet grains is caused by the presence of capillary bridges formed at the points of contact. The finite strength of these liquid bonds is responsible for a transition from a quiescent to a fluidized state under applied shear stress. This fluidization transition is studied in a MD-type simulation in a two dimensional assembly of bidisperse discs under the action of a spatially heterogeneous external force. Capillary interaction is modeled as a short ranged but hysteretic attractive force between discs with soft core repulsion. Besides the fluidization threshold we studied the spatial and temporal distribution of granular temperature, shear rate, stress, local packing fraction, and density of capillary bridges in both the fluidized and the quiescent state. The local viscosity η of the fluidized state is dominated by the local packing fraction ρ and diverges as η ∝ (ρc−ρ)−1.1 upon approaching random close packing (ρc≈ 0.85).