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

Abstract

With a 3D discrete-element method specially developed with adhesive contact mechanics, random loose packings of uniform spherical micron-sized particles are fully investigated. Characterized by a dimensionless adhesion parameter Ad proposed in the previous work, four packing regimes are identified: random close packing (RCP) regime with Ad<0.01; random loose packing (RLP) regime with 0.01<Ad<1; adhesion regime with 1<Ad<20 and an asymptotic limit regime with Ad>20. The evolution of the radial distribution function with respect to Ad is analyzed and divided into three stages. Force distribution of these adhesive loose packings follows P(f)~fθ for small forces and P(f)~e−βf for big forces, respectively, which shares a similar form with that in packings without adhesion but results in distinct exponents of θ=0.879, β=0.839 for normal forces. A local mechanical equilibrium analysis demonstrates that adhesion enhances both sliding and rolling resistance so that the fairly loose packing structures of adhesive particles can still be mechanically stable.