Granular shearing in a Couette geometry
In collaboration with people from ESPCI, Paris and Duke
University we have been engaged in experiments on a
two-dimensional Couette shear-cell.
The experiment was build by Dan Howell and Prof. Bob
Behringer from Duke
University and transported to Paris where the experiments were
Picture and schematic drawing of the experiment.
We study the mean and statistical kinetic properties of
slow shear flow in the shear gap.
Using particle tracking techniques, we measure the spin,
transport velocities and the associated density
variations during steady state shearing.
Below, a film sequence of the shear is shown. The disks have black markers
for later identification and tracking.
Shearing sequence used for disk tracking (3 frames/s).
Because the particles are photoelastic, it is also possible to infer
information on the stress state of the system.
The photoelastic effect causes the polarization of light comming from below
to rotate. Thus, disks under stress will show up as bright areas.
For more details, please see the page of Dan Howell.
Below is a film sequence of the forcechains as the system is sheared
(Greyscale is reversed, dark is high forces).
Forcechains under shearing (1 frame/s).
Notice the very rapid force-fluctuations compared to the typical velocity
of individual disks. Unfortunately the sampling time is not fast enough to
resolve the formation and decay in detail. Below is a film of a smaller
section close to the shearing wheel sample at 25 frames/s.
Forcechains under shearing (25 frames/s).
D. W. Howell, R. B. Behringer and C. T. Veje
Stress Fluctuations in
a 2D Granular Couette Experiment: A Critical Transition ,
Phys. Rev. Lett., (1999)
[gzipped ps ( k)]
C. T. Veje, D. W. Howell and R. B. Behringer,
Kinematics of a 2D granular Couette experiment at the transition to shearing ,
Phys. Rev. E, 59 739 (1999)
[gzipped ps (600 k)]
C. T. Veje, D. W Howell, R. B. Behringer, S. Schollmann, S. Luding and
H. J. Herrmann,
Fluctuations and Flow for Granular Shearing,
in H. J. Herrmann, J-P. Hovi and S. Luding, editors
Physics of dry granular media,
NATO ASI Series. Kluwer Academic Publishers, (1998)
[gzipped ps (250 k)]