Avalanches, thresholds, and diffusion in mesoscale amorphous plasticity.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Statistical Mechanics

Background:

• Amorphous materials exhibit complex behaviors under stress, particularly in steady-state shear flow.
• Understanding relaxation events and their statistical properties is crucial for characterizing material response.
• Previous models often simplify the interplay between stress, strain, and system dynamics.

Purpose of the Study:

• To investigate the mesoscale model for amorphous matter in athermal, quasistatic (a-AQS) steady-state shear flow.
• To analyze the scaling behavior of relaxation events, static properties, and long-time correlations with system size.
• To clarify the relationship between stress relaxation avalanches, diffusive behavior, and local threshold distributions.

Main Methods:

• Mesoscale modeling of amorphous matter under athermal, quasistatic shear flow.
• Analysis of scaling with lateral system size (L) for stress relaxation (S), mean-squared displacement (M), and load increments (Δγ).
• Investigation of local stress thresholds (x) and long-time correlations using single-particle tracer statistics.

Main Results:

• Distinct distributions for stress relaxation (S) and mean-squared displacement (M), with a correlation S∼M^0.65.
• Local threshold distribution P(x) shows size-dependent scaling P(x)|x=0 ∝ L^-0.6.
• Diffusion coefficient is determined by average load increment and M scaling, not directly by S.

Conclusions:

• The study further defines the athermal, quasistatic (a-AQS) universality class for amorphous matter.
• It clarifies the connection between stress relaxation events and emergent diffusive behavior.
• The research elucidates the relationship between local stress thresholds and the statistics of dynamic events.