Coexistence and transition between shear zones in slow granular flows

Area of Science:

• Granular physics
• Rheology of granular materials

Background:

• Understanding granular flow is crucial in various industrial and geological processes.
• Previous models often simplify the complex behavior of granular materials under shear.

Purpose of the Study:

• To investigate novel strain localization phenomena in slow granular flows.
• To analyze the formation and control of shear zones in granular media.
• To validate a theoretical model against experimental observations.

Main Methods:

• Experiments conducted using a split-bottom Couette cell to study slow granular flows.
• Observation and analysis of flow profiles and strain localization features.
• Application of the fluctuating band model to fit experimental data.

Main Results:

• Observed novel strain localization with simultaneous shear zone formation in bulk and boundaries.
• Demonstrated that the fluctuating band model, with a single parameter (relative friction coefficient, μ(rel)), accurately fits experimental data across various conditions.
• Showed that μ(rel) controls the formation of multiple shear zones.
• Identified spontaneous symmetry breaking of initial states below a critical shear velocity threshold.
• Observed a dynamical transition between asymmetric flow states dependent on shear strength.

Conclusions:

• The study elucidates complex flow behaviors in granular materials driven by simultaneous shear zone formation.
• The fluctuating band model provides a robust framework for predicting granular flow under varying conditions.
• The relative friction coefficient is a key parameter governing shear zone dynamics and flow asymmetry.