3 research outputs found
Transients in sheared granular matter
As dense granular materials are sheared, a shear band and an anisotropic
force network form. The approach to steady state behavior depends on the
history of the packing and the existing force and contact network. We present
experiments on shearing of dense granular matter in a 2D Couette geometry in
which we probe the history and evolution of shear bands by measuring particle
trajectories and stresses during transients. We find that when shearing is
stopped and restarted in the same direction, steady state behavior is
immediately reached, in agreement with the typical assumption that the system
is quasistatic. Although some relaxation of the force network is observed when
shearing is stopped, quasistatic behavior is maintained because the contact
network remains essentially unchanged. When the direction of shear is reversed,
a transient occurs in which stresses initially decrease, changes in the force
network reach further into the bulk, and particles far from the wheel become
more mobile. This occurs because the force network is fragile to changes
transverse to the force network established under previous shear; particles
must rearrange before becoming jammed again, thereby providing resistance to
shear in the reversed direction. The strong force network is reestablished
after displacing the shearing surface , where is the mean grain
diameter. Steady state velocity profiles are reached after a shear of . Particles immediately outside of the shear band move on average less than
1 diameter before becoming jammed again. We also examine particle rotation
during this transient and find that mean particle spin decreases during the
transient, which is related to the fact that grains are not interlocked as
strongly.Comment: 7 pages, 11 figures, accepted to Eur. Phys. J. E, revised version
based on referee suggestion