Pre-yielding mechanical response near the jamming transition.

Area of Science:

• Physics
• Materials Science
• Rheology

Background:

• Jammed packings of frictionless particles exhibit anomalous mechanical and rheological properties under shear.
• Two key anomalies include frequency-dependent scaling (G(ω) ~ ω^1/2) and strain-dependent softening (G(γ) ~ γ^-1/2).
• These behaviors are observed above the jamming transition point (φJ) and their range broadens as φJ is approached.

Purpose of the Study:

• Investigate the mechanical response in the regime where frequency and strain anomalies coexist near the jamming transition.
• Explore the coexistence of linear-response and quasi-static anomalies in jammed systems.
• Characterize nonlinear viscoelastic behavior in the vicinity of the jamming transition.

Main Methods:

• Numerical analysis of jammed packings of frictionless particles.
• Application of two rheological protocols: oscillatory shear and transient stress relaxation.
• Investigation of systems near the jamming transition point (φJ).

Main Results:

• Mechanical responses do not follow a simple superposition of the two known algebraic relaxations.
• Rich nonlinear viscoelastic behavior is observed both above and below the jamming transition point (φJ).
• The study highlights complex interactions between frequency and strain dependencies in jammed systems.

Conclusions:

• The mechanical response of jammed packings near the jamming transition is complex and exhibits nonlinear viscoelasticity.
• Simple superposition models fail to capture the observed behavior.
• Nonlinear effects are present even below the jamming transition point, suggesting a more nuanced understanding is required.