Computer simulation of model cohesive powders: Plastic consolidation, structural changes and elasticity under isotropic loads

TL;DR

This study uses Discrete Element simulations to analyze the structural and elastic behavior of a 2D cohesive powder model under isotropic loads, revealing three consolidation stages and the micro-mechanical origins of elasticity and plasticity.

Contribution

It provides a detailed characterization of the three-stage consolidation process and links microstructural changes to macroscopic elastic and plastic properties in cohesive powders.

Findings

Void ratio varies linearly with log pressure in stage II

Elastic moduli increase significantly during consolidation

Plastic deformation involves minimal topology changes, dominated by junction bending

Abstract

The quasistatic behavior of a simple 2D model of a cohesive powder under isotropic loads is investigated by Discrete Element simulations. The loose packing states, as studied in a previous paper, undergo important structural changes under growing confining pressure P, while solid fraction \Phi irreversibly increases by large amounts. The system state goes through three stages, with different forms of the plastic consolidation curve \Phi(P*), under growing reduced pressure P* = Pa/F0, defined with adhesion force F0 and grain diameter a. In the low-confinement regime (I), plastic compaction is negligible, and the structure is influenced by the assembling process. The following stage (regime II) is independent of initial conditions. The void ratio varies linearly with log P, as described in the engineering literature. In the last stage of compaction (III), a maximum solid fraction is approached, and properties of cohesionless granular packs are retrieved. Under consolidation, while the fractal range of density correlations decreases, force patterns reorganize, and elastic moduli increase by a large factor. Plastic deformation events correspond to very small changes in the network topology, while the denser regions tend to move like rigid bodies. Elastic properties are dominated by the bending of thin junctions in loose systems. For growing RR those tend to reduce to particle chains, the folding of which, rather than tensile ruptures, controls plastic compaction.