Monodisperse Dry Granular Flows on Inclined Planes : Role of Roughness

TL;DR

This study investigates how the roughness of inclined planes affects the friction and flow dynamics of monodisperse dry granular materials, revealing a maximum friction at a specific roughness independent of slope angle.

Contribution

It introduces a geometrical model predicting the roughness at maximum friction based on bead and bump sizes, validated by experimental data across various roughness levels.

Findings

Maximum friction occurs at a specific relative roughness.

The model accurately predicts the roughness for maximum friction.

Surface irregularities influence the friction behavior.

Abstract

Recent studies have pointed out the importance of the basal friction on the dynamics of granular flows. We present experimental results on the influence of the roughness of the inclined plane on the dynamics of a monodisperse dry granular flow. We found experimentally that it exists a maximum of the friction for a given relative roughness. This maximum is shown to be independent of the angle of the slope. This behavior is observed for four planes with different bump sizes (given by the size of the beads glued on the plane) from 200 microns to 2 mm. The relative roughness corresponding to the maximum of the friction can be predicted with a geometrical model of stability of one single bead on the plane. The main parameters are the size of the bumps and the size of the flowing beads. In order to obtain a higher precision, the model also takes into account of the spacing between the bumps of the rough plane. Experimental results and model are in good agreement for all the planes we studied. Other parameters, like the sphericity of the beads, or irregularities in the thickness of the layer of glued particles, are shown to be of influence on the friction.