Additional jamming transition in 2D bidisperse granular packings

TL;DR

This paper identifies two distinct jamming transitions in 2D bidisperse granular packings, including a novel transition where small particles jam into voids at a critical concentration and size ratio.

Contribution

It reveals a second jamming transition specific to small particles in 2D bidisperse systems, extending understanding from previous 3D studies.

Findings

Two separate jamming transitions identified

Critical small-particle concentration and size ratio determined

Second transition occurs at a well-defined point in parameter space

Abstract

We present a jamming diagram for 2D bidisperse granular systems, capturing two distinct jamming transitions. The first occurs as large particles form a jammed structure, while the second, emerging at a critical small-particle concentration, $X_{\mathrm{S}}^{*} \approx 0.21$, and size ratio, $\delta^{*} \approx 0.25$, involves small particles jamming into the voids of the existing large-particle structure upon further compression. Below this threshold, small particles fill voids within the large-particle network, increasing packing density. Beyond this point, excess small particles disrupt efficient packing, resulting in looser structures. \jp{These results, consistent with previous 3D studies, demonstrate that the second transition occurs at a well-defined point in the $(X_{\mathrm{S}}, \delta)$ plane, independent of dimensionality, likely driven by the geometric saturation of available space around particles, void closure, and structural arrangement.