Weak Agitations, Zero Yield Stress and Smooth Flows in Granular Media

Condensed Matter lunchtime seminar

Weak Agitations, Zero Yield Stress and Smooth Flows in Granular Media

  • Event time: 1:00pm
  • Event date: 19th May 2006
  • Speaker: Martin van Hecke (Leiden University)
  • Location: Room 2511,

Event details

A novel state of granular matter, a so-called stationary granular fluid, which combines a solid-like appearance with a fluid-like response to external stresses has recently been created in our lab. The trick is to locally shear and stir a layer of sand and probe its mechanical response in far-away regions where the material remains stationary. In contrast to its solid-like appearance, we observed that an intruder placed into these far-away zones sinks into the sand. Our present data suggests that the yielding stress is zero in these stationary zones, just like in a simple liquid -- in complete disagreement with the classical view of granular media where (stationary or flowing) appearance and yield strength are directly linked.

We believe that this behavior is caused by tiny agitations of the grains, which lead to large fluctuations of the contact forces --- deformations on the order of nanometers are sufficient to cause order one changes in contact force for millimetric glass beads. Consequences for the theory of slow grain flows and preliminary experiments in which the propagation of these agitations are manipulated will be presented.

This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..

Find out more about Condensed Matter lunchtime seminars.