Three-dimensional simulations of nanopowder compaction processes by granular dynamics method

Abstract

In order to describe and to study the processes of cold compaction within the discrete element method a three-dimensional model of nanosized powder is developed. The elastic forces of repulsion, the tangential forces of "friction" (Cattaneo-Mindlin), and the dispersion forces of attraction (van der Waals-Hamaker), as well as the formation and destruction of hard bonds between the individual particles are taken into account. The monosized powders with the size of particles in the range 10-40 nm are simulated. The simulation results are compared to the experimental data of the alumina nanopowders compaction. It is shown that the model allows us to reproduce experimental data reliably and, in particular, describes the size effect in the compaction processes. A number of different external loading conditions is used in order to perform the theoretical and experimental researches. The uniaxial compaction (the closed-die compaction), the biaxial (radial) compaction, and the isotropic compaction (the cold isostatic pressing) are studied. The real and computed results are in a good agreement with each other. They reveal a weak sensitivity of the oxide nanopowders to the loading condition (compaction geometry). The application of the continuum theory of the plastically hardening porous body, which is usually used for the description of powders, is discussed.

Influence of particle size distribution on nanopowder cold compaction processes

“…[12] is used, which allows producing isotropic and homogeneous structures in the form of connected 2D-periodical cluster. Figure 1 shows examples of initial structures.…”

“…The parameters of interparticle interactions correspond to oxide nanosized powders having weak (I type systems) or strong (II type systems) agglomeration tendency [12,13]. The theoretical model of [12,13] includes the contact interaction laws, such as the modified Hertz law, which describes the elastic repulsion of particles, the linearized Cattaneo -Mindlin law [14,15], which describes the "friction" forces at particle shift, the Lurie law [16], which describes the contact elasticity to the particle rolling, as well as modified Hamaker's formula [17], which describes the dispersion attractive forces, and (in the case of II type systems) the possibility of interparticle solid bridges formation [10].…”

“…Thereupon the direct simulations of nanopowders by the granular dynamics method, also known as the discrete element method [4,5,[7][8][9][10][11], have attractive prospects. Different regularities of nanopowder systems, for example, the size effect in nanopowder compaction processes, have been already investigated in the framework of the granular dynamics method [4,5,12,13]. Heretofore objects for numerical experiments are monodisperse systems [8,12,13], which consist of particles of the same size, or systems with very artificial particle size distributions, for example, the uniform distribution into the given narrow range of sizes [9].…”

“…Different regularities of nanopowder systems, for example, the size effect in nanopowder compaction processes, have been already investigated in the framework of the granular dynamics method [4,5,12,13]. Heretofore objects for numerical experiments are monodisperse systems [8,12,13], which consist of particles of the same size, or systems with very artificial particle size distributions, for example, the uniform distribution into the given narrow range of sizes [9]. This situation differs drastically from real experimental conditions [1][2][3]6].…”

Compaction simulation of nano-crystalline metals with molecular dynamics analysis

“…Boltachev et al [10] employed the granular dynamics method to simulate the quasi-static uniaxial compaction of nano-powders. They investigated the efficiency of particles size in the quasi-static compaction of nanopowders using the granular dynamic method [11].…”