Particle shape and the strengthening transition in 2D granular shearing
Abstract
We show experimentally that a slowly sheared 2D granular material undergoes a transition as the packing fraction γ is increased through a critical value, γc ~= 0.777 for disks and γc ~= 0.725 for pentagons. The experiment consists of ~ 3000 photoelastic disks or pentagons confined to a plane Couette geometry by Plexiglas sheets, an inner disk, and an outer ring. The assembly is sheared by rotating the inner disk. Photoelasticity of the particles allows us to visualize the local stress by observing the experiment through crossed circular polarizers. We find stress and position information simultaneously using a two camera setup. Here we examine similarities and differences involving particle shape. Although there are differences in dilation, velocity, and stress characteristics between the two sets of particles, we see similar changes with global packing fraction suggesting a robust transition. As γ arrow γc from above, the following occur: 1) The mean stress, σ, decreases dramatically; 2) slowing down occurs; 3) there are qualitative changes in the stress distributions and statistics; 4) the spatial network of stress chains changes, with long uninterrupted nearly radial chains occurring intermittently in space and time near γc and a more complex network occurring throughout the system for larger packing fraction.
- Publication:
-
APS Southeastern Section Meeting Abstracts
- Pub Date:
- November 1999
- Bibcode:
- 1999APS..SES..ED11H