Compaction force in a confined granular column

Area of Science:

• Physics
• Materials Science
• Fluid Dynamics

Background:

• Granular materials exhibit complex behaviors under confinement.
• Janssen's theory describes pressure in granular materials but may not capture all phenomena.

Purpose of the Study:

• To experimentally determine the force required to push a confined granular column.
• To investigate the influence of column height, sphere diameter, cylinder diameter, and displacement velocity on this force.
• To identify rate-dependent behaviors in dense granular flows.

Main Methods:

• Utilized a material testing system machine for simultaneous force and displacement measurements.
• Conducted experiments with varying sphere diameters, cylinder diameters, and piston displacement velocities.
• Focused on granular columns confined within a cylinder.

Main Results:

• The force required to displace the granular column increased significantly with column height, aligning with Janssen's theory.
• An unexpected finding was that the force also increased with the piston displacement velocity.
• Observed a transition to rate-dependent behavior in dense granular flows.

Conclusions:

• Granular column displacement force is dependent on column height and, notably, on the rate of displacement.
• The observed velocity dependence suggests a shift towards rate-dependent phenomena in dense granular flow regimes.
• These findings contribute to a deeper understanding of granular material mechanics and flow dynamics.