Computer simulation of model cohesive powders: influence of assembling procedure and contact laws on low consolidation states

TL;DR

This study uses molecular dynamics simulations to explore how assembling procedures and contact laws influence the microstructure and mechanical properties of cohesive powders, revealing the impact of parameters like pressure and rolling resistance.

Contribution

It provides new insights into how assembling procedures and contact laws affect the microstructure and force networks in cohesive powders through detailed simulations.

Findings

Microstructure varies with assembling procedure and contact laws.

Force networks form hyperstatic clusters connected by nearly unstressed arms.

Density correlations exhibit fractal structures with a density-dependent blob size.

Abstract

The structure and mechanical properties of a simple two-dimensional model of a cohesive powder are investigated by molecular dynamics simulations. Micromechanical ingredients involve elasticity, friction, a short range attraction and, possibly, rolling resistance (RR) in contacts. The microstructure of the cohesive packing varies according to the assembling procedure, from rather densely packed if isolated particles are directly compressed to much looser if the formation of large aggregates is allowed prior to compression. A crucial parameter is the ratio P*= Pa/F0 of applied pressure P, acting on grains of diameter $a$, to maximum tensile contact force F0. At low P* the final structure depends on the level of velocity fluctuations at the early stages of cluster aggregation. With RR the coordination number approaches 2 in the limit of low initial velocities or large rolling friction. The force network generally comprises small hyperstatic clusters with forces of the order of F0, joined by nearly unstressed, barely rigid arms. As P* grows, it quickly rearranges into force chain-like patterns. Density correlations witness a fractal structure, with dimension Df, up to some density-dependent blob size. WIth RR Df coincides with the ballistic aggregation result, despite a possibly different connectivity. Possible effects of some parameters on material strength are evoked.