We present results from a planar shear experiment in which a two-dimensional horizontal granular assembly of pentagonal particles sheared between two parallel walls is subjected to external vibration. Particle tracking and photoelastic measurements are used to quantify both grain scale motion and interparticle stresses with and without imposed vibrations. We characterize the particle motion in planar shear and find that flow of these strongly interlocking particles consists of transient vortex motion with a mean flow given by the sum of exponential profiles imposed by the shearing walls. Vibration is applied either through the shearing surface or as bulk vertical vibration of the entire shearing region with dimensionless accelerations Γ=A(2πf)2/g≈0–2. In both cases, increasing amplitude of vibration A at fixed frequency f leads to failure of the force network, reduction in mean stress, and a corresponding reduction in imposed strain. Vibration of the shearing surface is shown to induce the preferential slipping of large-angle force chains. These effects are insensitive to changes in frequency in the range studied (f=30–120 Hz), as sufficiently large displacements are required to relieve the geometrical frustration of the jammed states.
Physical Review E
Physics & Astronomy
Utter, Brian and Hoppmann, Eric P.. "Planar granular shear flow under external vibration." Physical Review E (2017) : 022903.