Nonlocal Effects Reflect the Jamming Criticality in Frictionless Granular Flows Down Inclines

Area of Science:

• Physics of granular materials
• Soft matter physics
• Non-equilibrium statistical mechanics

Background:

• Jamming transition in granular materials exhibits complex behaviors like hysteresis and nonlocal effects.
• The precise origins of these phenomena, particularly the role of friction, remain poorly understood.
• Existing models struggle to disentangle generic collective effects from friction-specific interactions.

Purpose of the Study:

• To experimentally investigate a frictionless granular layer model to isolate generic collective effects.
• To determine the influence of layer thickness on jamming transition phenomenology, specifically hysteresis and stability.
• To clarify the underlying mechanisms responsible for nonlocal effects in granular flow.

Main Methods:

• Experimental study of a frictionless granular layer flowing down an inclined plane.
• Systematic variation of layer thickness to observe changes in flow behavior.
• Analysis of avalanche angle hysteresis and rheological properties.
• Collapse of rheological data onto a master curve to identify scaling laws.

Main Results:

• Thin frictionless granular layers exhibit no hysteresis in the avalanche angle.
• Layer stability increases significantly as the granular layer thickness decreases.
• Rheological data for various thicknesses collapse onto a single master curve, indicating universal behavior.
• The isostatic length (l*) governs boundary effects on granular flow, explaining nonlocal phenomena.

Conclusions:

• Nonlocal effects in granular flow are primarily a consequence of finite-size effects near a critical point.
• Friction is not essential for observing nonlocal effects; generic collective behavior dominates.
• The isostatic length (l*) is the critical length scale determining boundary influence on granular flow dynamics.