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DY: Fachverband Dynamik und Statistische Physik
DY 62: Poster - Dynamics
DY 62.18: Poster
Thursday, March 19, 2015, 16:00–18:00, Poster A
Friction with your neighbors? Think locally! — •Matthias Schröter1, Max Neudecker1, Cyprian Lewandowski2, Pascal Wieland2, Claus Heussinger2, Fabian Schaller3, and Gerd Schröder-Turk3 — 1Max Planck Institute for Dynamics and Self-Organization, Göttingen — 2Georg-August University of Göttingen — 3Friedrich-Alexander-Universität Erlangen-Nürnberg
Understanding how the number of contacts Z in a packing of particles depends on the global volume fraction φ is a fundamental questions in soft matter physics. If the particles under consideration are soft and frictionless spheres, such as emulsions and foams, assuming Z(φ) is reasonable because additional contacts are formed by the globally isotropic compression of the particles which also increases φ. However, in frictional granular media the control of φ is not achieved by compression but by changing the geometric structure of the sample; if we want to fill more grains into a container we do not compress them with a piston, but we tap the container a couple of times on the table.
But if Z and φ are not simultaneously controlled by a globally defined parameter such as pressure, the idea of a function Z(φ) runs into an epistemological problem. Contacts are now formed at the scale of individual particles and their neighbors, a scale where φ is undefined. What is therefore needed for the theoretical description of frictional particles is an ansatz which explains Z using only locally defined parameters. This poster reviews recent progress towards such a theory based on experimental results obtained by X-ray tomography of packings of spheres, ellipsoids, cylinders and tetrahedra.