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Avalanches in fine, cohesive powders
1Departmento de Electronica y Electromagnetismo, Universidad de Sevilla, Avenido Reina Mercedes s/n, 41012 Sevilla, Spain.
Summary
Avalanches in fine powders are deeper than expected due to cohesive forces, unlike dry sand. Increasing bed width reduces avalanche angle but increases depth, revealing the role of cohesion and boundary conditions.
Area of Science:
- Granular Physics
- Materials Science
- Rheology
Background:
- Avalanches in granular materials are typically studied in noncohesive systems like dry sand.
- Fine powders exhibit cohesive behavior due to interparticle forces, significantly impacting their flow dynamics.
- Understanding avalanche onset in cohesive granular media is crucial for various industrial and geological processes.
Purpose of the Study:
- To investigate the onset and characteristics of avalanches in fine, cohesive granular materials.
- To analyze the influence of bed width on avalanche properties such as angle and depth.
- To elucidate the role of powder cohesion and boundary conditions in governing avalanche behavior.
Main Methods:
- Experimental generation of shear stress by tilting a powder bed.
- Systematic variation of the initialized bed width.
- Macroscopic analysis using Coulomb's method of wedges.
Main Results:
- Avalanche angle decreases with increasing bed width.
- Avalanche depth increases with bed width, significantly exceeding particle size (several millimeters).
- Cohesion and boundary conditions fundamentally influence avalanche behavior in fine powders.
Conclusions:
- Fine cohesive powders exhibit avalanche behavior distinct from noncohesive grains.
- Dominance of van der Waals forces over particle weight in fine powders leads to open structures and behaviors resembling wet sand.
- The macroscopic analysis highlights the critical role of cohesion in granular material avalanches.
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