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Superlubricity in granular shear flows under external vibrations.

Diego Berzi^1,2, Melisa M Gianetti¹, Dalila Vescovi¹

¹Department of Civil and Environmental Engineering, Politecnico di Milano, 20133 Milano, Italy. diego.berzi@polimi.it.

|June 16, 2026

Summary

External vibrations can significantly reduce friction in granular flows. Applying oscillations to bumpy planes can lead to superlubricity, minimizing energy dissipation and improving shear resistance predictions.

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Area of Science:

Physics
Materials Science
Mechanical Engineering

Background:

Macroscopic friction in granular materials is a critical factor in various industrial processes.
Understanding and controlling friction in granular flows, especially under pressure, is essential for efficient material handling and design.
Existing methods for friction reduction in granular systems often have limitations.

Purpose of the Study:

To investigate the effectiveness of external vibrations in reducing macroscopic friction in granular flows.
To determine the conditions under which granular systems exhibit superlubric behavior.
To quantify energy dissipation and develop predictive criteria for shear resistance.

Main Methods:

Utilizing the discrete element method (DEM) to simulate granular flows between bumpy planes.
Applying external vibrations to one of the shearing planes.
Systematically varying parameters such as oscillation amplitude, frequency, and imposed pressure.

Main Results:

Achieved superlubricity (macroscopic friction < 0.01) with sufficiently large oscillation amplitudes.
Quantified the reduction in dissipated energy due to decreased macroscopic friction.
Identified the trade-off between reduced shear stress and applied vibrational energy.
Developed a phase diagram relating imposed pressure and oscillation velocity amplitude to shear resistance.

Conclusions:

External vibrations offer a viable method for drastically reducing friction in granular flows.
Superlubricity in granular systems can be achieved through controlled oscillations.
The proposed phase diagram and criteria provide a framework for predicting and controlling shear resistance in vibrated granular flows.