We report experimental results on the dynamics of a granular packing submitted to high-intensity focused ultrasound. Acoustic radiation pressure is shown to remotely induce local rearrangements within a pile as well as global motion around the focal spot in an initially jammed system. We demonstrate that this fluidization process is intermittent for a range of acoustic pressures and hysteretic when the pressure is cycled. Such a first-order-like unjamming transition is reproduced in numerical simulations in which the acoustic pressure field is modeled by a localized external force. Further analysis of the simulated packings suggests that in the intermittent regime unjamming is not associated with any noticeable prior structural signature. A simple two-state model based on effective temperatures is proposed to account for these findings.
@article{arxiv.1411.6033,
title = {Grains unchained: local fluidization of a granular packing by focused ultrasound},
author = {Pierre Lidon and Nicolas Taberlet and Sebastien Manneville},
journal= {arXiv preprint arXiv:1411.6033},
year = {2016}
}