Granular Segregation Mechanisms by Cyclic Shear

TL;DR

This study uses X-ray tomography to uncover how cyclic shear causes segregation in granular materials, revealing convection-driven and structural asymmetry mechanisms that influence particle distribution.

Contribution

It identifies two novel segregation mechanisms in cyclically sheared granular media: convection-driven upward movement and structural asymmetry effects.

Findings

Big tracers rise to the surface due to convection.

Arching effects induce upward displacement of large tracers.

Segregation is driven by both convection and structural asymmetry.

Abstract

We present an X-ray tomography study of the segregation mechanisms of tracer particles in a three-dimensional cyclically sheared bi-disperse granular medium. Big tracers are dragged by convection to rise to the top surface and then remain trapped there due to the small downward convection cross-section, which leads to segregation. Additionally, we also find that the local structural up-down asymmetry due to arching effect around big tracers will induce the tracers to have a net upward displacement against its smaller neighbors, which is another mechanism for segregation.