Shear modulus and dilatancy softening in granular packings above jamming

Area of Science:

• Granular physics
• Soft matter physics
• Materials science

Background:

• The jamming transition marks a critical point in granular materials, transitioning from fluid-like to solid-like behavior.
• Understanding the mechanical response of granular packings near jamming is crucial for predicting material properties.

Purpose of the Study:

• To experimentally investigate the shear response of bidisperse frictional grains across the jamming transition.
• To quantify constitutive relations and characterize nonlinear effects at small strain amplitudes.

Main Methods:

• Utilizing photoelasticity and particle tracking techniques to measure grain-scale shear strain and stresses.
• Inflating an intruder within a monolayer of grains to induce controlled shear.
• Analyzing mechanical responses for packing fractions near the jamming transition.

Main Results:

• Observed strong nonlinear effects at the jamming transition, including softening of shear modulus and dilatancy at small strains.
• Identified a critical strain where effective linearity is recovered, with its scaling determined by the distance to jamming.
• Characterized a spatial crossover in stress and strain profiles between linear and nonlinear regimes, with a diverging crossover length at jamming.

Conclusions:

• Constitutive laws and mechanical equilibrium accurately predict observed stress and strain profiles near the jamming transition.
• The study provides quantitative insights into the nonlinear mechanical behavior of granular materials at the jamming point.
• The findings contribute to a deeper understanding of the fundamental physics governing granular matter.