Pressure-Dependent Friction on Granular Slopes Close to Avalanche.

Area of Science:

• Physics
• Geophysics
• Robotics

Background:

• Understanding granular material dynamics is crucial for predicting object stability.
• Avalanche thresholds in granular media are complex phenomena influenced by various factors.
• Friction in granular systems deviates from classical models under certain conditions.

Purpose of the Study:

• To investigate the influence of surface deformations on object sliding near the avalanche threshold.
• To determine how object weight affects stability and friction on inclined granular surfaces.
• To explore potential applications in locomotion for devices and animals.

Main Methods:

• Experimental setup involving objects sliding on inclined granular surfaces.
• Controlled variation of object weight to observe surface deformation effects.
• Measurement of friction coefficients and analysis of stability criteria.

Main Results:

• Object stability is primarily driven by surface deformations, not solely by weight.
• Heavy objects create stabilizing deformations (footprints), while light objects cause minimal disturbance.
• Intermediate object weights induce surface deformations leading to sliding, with friction minimal at a characteristic pressure.
• Observed friction coefficients deviate from Amontons-Coulomb laws.

Conclusions:

• Surface deformation is a key factor in granular object stability, overriding simple frictional models.
• The relationship between pressure, deformation, and friction is non-monotonic.
• Findings have implications for designing legged robots and understanding animal locomotion on granular terrains.