Stress-strain behavior and geometrical properties of packings of elongated particles

TL;DR

This study uses numerical simulations to analyze how particle elongation influences the shear strength, microstructure, and packing properties of granular media, revealing that elongation increases shear strength and affects contact networks.

Contribution

It provides new insights into the microstructural mechanisms by which particle elongation affects granular material behavior, including force transmission and anisotropy.

Findings

Shear strength increases linearly with elongation.

Force transmission is mainly through cap-to-side contacts.

Solid fraction first increases then decreases with elongation.

Abstract

We present a numerical analysis of the effect of particle elongation on the quasistatic behavior of sheared granular media by means of the Contact Dynamics method. The particle shapes are rounded-cap rectangles characterized by their elongation. The macroscopic and microstructural properties of several packings subjected to biaxial compression are analyzed as a function of particle elongation. We find that the shear strength is an increasing linear function of elongation. Performing an additive decomposition of the stress tensor based on a harmonic approximation of the angular dependence of branch vectors, contact normals and forces, we show that the increasing mobilization of friction force and the associated anisotropy are key effects of particle elongation. These effects are correlated with partial nematic ordering of the particles which tend to be oriented perpendicular to the major principal stress direction and form side-to-side contacts. However, the force transmission is found to be mainly guided by cap-to-side contacts, which represent the largest fraction of contacts for the most elongated particles. Another interesting finding is that, in contrast to shear strength, the solid fraction first increases with particle elongation, but declines as the particles become more elongated. It is also remarkable that the coordination number does not follow this trend so that the packings of more elongated particles are looser but more strongly connected.