Sheared Amorphous Packings Display Two Separate Particle Transport Mechanisms.

Area of Science:

• Physics of granular materials
• Soft condensed matter physics
• Statistical mechanics

Background:

• Shearing granular materials causes nonaffine displacements, crucial for plasticity and mechanical behavior.
• Shear transformation zones, quantified by local deviation from affine deformation (D_min^2), are a known mechanism.
• Existing models focus on local diffusive motion and shear transformation zones.

Purpose of the Study:

• To identify and characterize additional mesoscopic transport mechanisms in sheared granular materials.
• To investigate the interplay between known and novel transport phenomena.
• To explore the implications for material memory effects.

Main Methods:

• Analysis of sheared frictional athermal disc packings.
• Application of diffusion tensor analysis to identify mesoscopic transport.
• Correction for the newly identified transport to re-evaluate D_min^2.

Main Results:

• A second, superimposed mesoscopic transport mechanism was identified in homogeneous systems.
• The trace of the diffusion tensor equals the classic D_min^2 after correcting for this new mechanism.
• This mechanism is robust across varying volume fractions, friction coefficients, and shear reversals.

Conclusions:

• Granular material shearing involves at least two superimposed mesoscopic transport mechanisms.
• The newly discovered mechanism is fundamental and influences the interpretation of D_min^2.
• The mechanism's consistency suggests relevance for understanding memory effects in granular systems.