Kerstin Nordstrom, Emily Lim, Matthew Harrington, Wolfgang Losert
We study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. Specifically, we vary the amount of prestrain on the sample, strengthening the force chains within the system. We find this affects only the prefactor of linear depth-dependent term in the stopping force. Using a laser sheet scanning technique to visualize internal grain motion, a high-speed camera, and particle tracking, we can measure the trajectory of each grain throughout an impact event. Microscopically, our results indicate that weaker initial force chains result in more irreversible, plastic rearrangements during impact, suggesting friction does play a role. However, by comparing results of wet and dry systems, we infer that friction is not the primary cause of the linear depth-dependent term. These results suggest the depth-dependent mode of energy dissipation is likely acoustic in nature, governed by enhanced normal contacts between grains.
View original:
http://arxiv.org/abs/1304.6419
No comments:
Post a Comment