Stress relaxation in viscous soft spheres.

Area of Science:

• Soft Matter Physics
• Computational Materials Science
• Statistical Mechanics

Background:

• Stress relaxation is crucial for understanding the mechanical behavior of soft materials.
• Athermal viscous soft sphere packings exhibit complex responses near the jamming transition.
• Characterizing relaxation times is key to distinguishing viscous and elastic behaviors.

Purpose of the Study:

• To investigate stress relaxation in soft sphere packings under varying strain and pressure.
• To identify and characterize relaxation time scales in both linear and nonlinear response regimes.
• To explore the relationship between bulk mechanical relaxation and microscopic particle motion.

Main Methods:

• Molecular dynamics simulations were employed to model stress relaxation tests.
• Systematic variation of applied strain step amplitude and initial pressure was performed.
• Analysis focused on the strain dependence of relaxation time and particle velocity evolution.

Main Results:

• Two distinct plateaus in relaxation time were observed, corresponding to linear and nonlinear regimes.
• The height of these plateaus follows an inverse power-law scaling with the distance to jamming.
• A correlation was found between bulk mechanical relaxation and the degree of non-affinity in particle velocities.

Conclusions:

• The study reveals distinct relaxation regimes in soft sphere packings near jamming.
• Scaling laws governing relaxation times provide insights into the proximity of the jamming transition.
• Microscopic particle dynamics, specifically non-affinity, are linked to macroscopic stress relaxation.