Computer simulation of random loose packings of micro-particles in presence of adhesion and friction

TL;DR

This study uses a new 3D discrete-element simulation to explore how adhesion and friction influence the packing density and force distribution of micron-sized spherical particles, revealing distinct regimes based on an adhesion parameter.

Contribution

Developed a novel 3D discrete-element method incorporating adhesive contact mechanics to analyze random loose packings of micro-particles, identifying regimes and force distribution characteristics.

Findings

Large velocity, size, or weak adhesion lead to denser packings.

Four regimes identified based on adhesion parameter $Ad$.

Force distribution follows specific power-law and exponential forms.

Abstract

With a novel 3D discrete-element method specially developed with adhesive contact mechanics, random loose packings of uniform spherical micron-sized particles are fully investigated. The results show that large velocity, large size or weak adhesion can produce a relatively dense packing when other parameters are fixed, and these combined effects can be characterized by a dimensionless adhesion parameter ( $Ad=\omega/2\rho_pU^2_0R$). Four regimes are identified based on the value of $Ad$: RCP regime with $Ad<\sim 0.01$; RLP regime with $\sim 0.01<Ad<1$; adhesion regime with $1<Ad<20$ and an asymptotic regime with $Ad>20$. Force distribution of these adhesive loose packings follows $P(f)\sim f^\theta$ for small forces and $P(f)\sim \exp^{-\beta f}$ for big forces, respectively, which shares a similar form with that in packings without adhesion but results in distinct exponents of $\theta=0.879$, $\beta=0.839$. A local mechanical equilibrium analysis shows that adhesion enhances both sliding and rolling resistance so that fewer neighbours are needed to satisfy the force and torque balance.