Orientational Ordering in Athermally Sheared, Aspherical, Frictionless Particles.

Area of Science:

• Physics
• Materials Science
• Computational Science

Background:

• Understanding the mechanical behavior of granular materials is crucial for various engineering applications.
• Particle shape and interactions significantly influence bulk properties like jamming and flow.
• Previous studies often focused on spherical particles, limiting insights into anisotropic effects.

Purpose of the Study:

• To investigate the role of particle shape, specifically asphericity, on the orientational ordering and jamming behavior of granular materials.
• To explore the transition from anisotropic (spherocylinders, ellipsoids) to more isotropic (spherical) particle shapes under shear.
• To analyze particle rotation and contact mechanics in relation to particle shape and packing fraction.

Main Methods:

• Numerical simulations of uniform athermal shearing were performed.
• Two-dimensional bidisperse, frictionless spherocylinders and three-dimensional prolate ellipsoids were modeled.
• The nematic order parameter (S2) was analyzed as a function of asphericity (α) and packing fraction (ϕ).

Main Results:

• The nematic order parameter (S2) exhibited nonmonotonic behavior with respect to packing fraction (ϕ).
• As particle asphericity (α) approached zero, S2 remained finite at and above the jamming transition.
• Sheared particles continued to rotate above jamming, with contacts favoring the particles' narrowest width.

Conclusions:

• The approach to spherical particle shapes appears to introduce a singularity in the orientational ordering of sheared granular systems.
• Particle shape plays a critical role in determining the mechanical response and contact geometry of granular materials near jamming.
• These findings have implications for designing and predicting the behavior of granular materials with complex particle morphologies.