Packing Fractions and Maximum Angles of Stability of Granular Materials

TL;DR

This study investigates how packing fraction influences the stability of granular heaps in rotating drums, revealing that higher packing increases stability for a fixed shape, but lower packing shapes can form more stable heaps overall.

Contribution

It uncovers the dual role of packing fraction in granular stability and highlights the surface configuration's importance in stability analysis.

Findings

Stability increases with packing fraction for fixed grain shape.

Shapes with lower average packing fractions tend to form more stable heaps.

Surface configuration predominantly influences heap stability.

Abstract

In two-dimensional rotating drum experiments, we find two separate influences of the packing fraction of a granular heap on its stability. For a fixed grain shape, the stability increases with packing fraction. However, in determining the relative stability of different grain shapes, those with the lowest average packing fractions tend to form the most stable heaps. We also show that only the configuration close to the surface of the pile figures prominently.