Granular avalanche statistics in rotating drum with varied particle roughness

Abstract

We experimentally investigate the avalanche statistics of dry granular materials in a slowly rotating drum for five types of beads with varied surface roughness. For all beads, two distinct angles, i.e., repose angle $\theta_r$ and maximal angle $\theta_m$, can be clearly defined, and the avalanche size distributions $P( δ\theta)$ are Gaussian-like. $\theta_r$, $\theta_m$, and the span in $P( δ\theta)$ are all positively correlated with bead surface roughness. This observation thus contrasts with a power-law $P( δ\theta)$ predicted by self-organized criticality, but is reminiscent of a first-order phase transition. We speculate that both the inertia effect and the velocity-weakening mechanism during an avalanche process can enhance the first-order features, which are however absent in plasticity of sheared amorphous solids. We also discuss the dependence between $\theta_r$ and $\theta_m$ for various particles, as well as the correlation between starting and stopping angles for an individual avalanche.

Keywords

• granular materials
• avalanche
• rotating drum