Abstract
The Janssen effect is a unique property of confined granular materials experiencing gravitational compaction in which the pressure at the bottom saturates with an increasing filling height due to frictional interactions with side walls. In this Letter, we replace gravitational compaction with frictional compaction. We study friction-compacted 2D granular materials confined within fixed boundaries on a horizontal conveyor belt. We find that even with high-friction side walls the Janssen effect completely vanishes. Our results demonstrate that gravity-compacted granular systems are inherently different from friction-compacted systems in at least one important way: vibrations induced by sliding friction with the driving surface relax away tangential forces on the walls. Remarkably, we find that the Janssen effect can be recovered by replacing the straight side walls with a sawtooth pattern. The mechanical force introduced by varying the sawtooth angle can be viewed as equivalent to a tunable friction force. By construction, this mechanical friction force cannot be relaxed away by vibrations in the system.
- Received 27 November 2013
DOI:https://doi.org/10.1103/PhysRevLett.112.188001
© 2014 American Physical Society
Focus
Granular Materials Aren’t Like Liquids, Except When They Are
Published 9 May 2014
Grain in a silo is supported to some extent by static friction with the walls, which couldn’t happen in a water-filled silo. But a similar granular material can behave more like water.
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