Experimental Study of Particle Interactions in Moderate to Dense Granular Shear Flows of Disks

To find the status of multiple collisions in transitional granular flow, moderate to densely packed monosized plastic disks were sheared in experimental 2D shear flow apparatus by applying shear strain rate in the range of 14.8 s−1 to 34.6 s−1. Application of high speed video camera and subsequent image processing techniques precisely measure the spatial positions of the particles involved in making the flow. Collision detection and contact duration finding algorithms were formulated to detect inter particle collision in each time step. The proportion of binary and multiple collisions was quantified in each time step. It is found that the contribution of multi particle collision is 13% for the lowest normalized solid fraction (ν∗ = 0.50) and 68% for the highest normalized solid fraction (ν∗ = 0.85) under consideration. The inter particle collision time is also found greater than binary collision time in all the flows under consideration. The group size is determined for each time step as an additional length scale associated with multi-particle interactions. Number of groups was made of more than two particles in all the flows under consideration, and the amount of such groups increased on increasing the solid fraction irrespective of the shear rate. In the dense cases (solid fraction > 0.60), rapid increase in the group size and the formation of occasional force chains should be attributed for the change in the stress generation pattern.