Regensburg 2010 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 13: Granular Matter/ Contact Dynamics II
DY 13.9: Talk
Wednesday, March 24, 2010, 11:45–12:00, H47
Yield stress and shear modulus in frictional granular packing — •Jean-Francois Metayer1, Donald Trey Suntrup III2, Harry Swinney2, Charles Radin3, and Matthias Schroeter1 — 1MPI for Dynamics and Selforganization, Göttingen, Germany — 2Center for Nonlinear Dynamics, University of Texas, Austin, USA — 3Departments of Mathematics, University of Texas, Austin, USA
A granular system is able to behave like a solid (a sand pile for example) or like a liquid depending on the shear stress imposed on the material. This study is focused on the phase transition between those two states and its goal is to obtain an experimental phase diagram of a granular media in three dimensions.
The yield stress of our granular media is obtained by measuring the force, F, needed to pull-up a paddled immersed in a granular bed as a function of its packing fraction and the depth of immersion. Fluctuations of F give us access to a measurement of the shear modulus, G, as a function of the same parameters. Results we present here clearly evidence that the value of the shear stress, needed to unjam our granular media, and its shear modulus are strongly related to the packing fraction: for low packing fraction (< ≈ 0.59) F and G are constant with φ whereas their value are highly dependant on φ for higher packing fraction.