Structural similarity between dry and wet sphere packings

TL;DR

This study reveals that the structural characteristics of dry and wet sphere packings are remarkably similar, despite significant differences in their mechanical properties caused by wetting liquids, with implications for modeling wet granular materials.

Contribution

The paper demonstrates that wetting liquids do not alter the structural arrangement of sphere packings, providing new insights into the relationship between structure and mechanics in wet granular matter.

Findings

Structural similarity between dry and wet packings in terms of contact number and Voronoi shape.

Number of liquid bridges per sphere approximately equals contact number plus two.

Mechanical differences are not due to structural differences, as shown by X-ray tomography.

Abstract

The mechanical properties of granular materials change significantly in the presence of a wetting liquid which creates capillary bridges between the particles. Here we demonstrate, using X-ray tomographies of dry and wet sphere packings, that this change in mechanical properties is not accompanied by structural differences between the packings. We characterize the latter by the average numbers of contacts of each sphere $\langle Z\rangle$ and the shape isotropy $\langle \beta_0^{2,0} \rangle$ of the Voronoi cells of the particles. Additionally, we show that the number of liquid bridges per sphere $\langle B\rangle$ is approximately equal to $\langle Z\rangle + 2$, independent of the volume fraction of the packing. These findings will be helpful in guiding the development of both particle-based models and continuum mechanical descriptions of wet granular matter.