Orientational arrest in dense suspensions of elliptical particles under oscillatory shear flows

We study the rheological response of dense suspensions of elliptical particles, with an aspect ratio equal to 3, under oscillatory shear flows and imposed pressure by numerical simulations. Like for the isotropic particles, we find that the oscillatory shear flows respect the Cox-Merz rule at large oscillatory strains but differ at low strains, with a lower viscosity than the steady shear and higher shear jamming packing fractions. However, unlike the isotropic cases (i.e., discs and spheres), frictionless ellipses get dynamically arrested in their initial orientational configuration at small oscillatory strains. We illustrate this by starting at two different configurations with different nematic order parameters and the average orientation of the particles. Surprisingly, the overall orientation in the frictionless case is uncoupled to the rheological response close to jamming, and the rheology is only controlled by the average number of contacts and the oscillatory strain. Having larger oscillatory strains or adding friction does, however, help the system escape these orientational arrested states, which are evolving to a disordered state independent of the initial configuration at low strains and ordered ones at large strains.

STRUCTURE AND MECHANICAL PROPERTIES OF POWDERS OBTAINED BY ELECTRODISPERGING COBALT-CHROMIUM ALLOY

The work presents the results of attestation of powders that were obtained from the KHMS "Cellite" alloy (Co - 63%, Cr - 27%, Mo - 5%, Ni - 2%, Fe - 2%) by electroerosive dispersion under various technological conditions (voltage from 100 V to 220 V, the capacitance of condenser from 15 μF to 50 μF, pulse frequency from 100 Hz to 200 Hz), and with using working fluids of different chemical composition and properties (water, kerosene, butyl alcohol). The study of the dispersion of the obtained powders, based on the results, established: the range of particle sizes is from 20 μm to 110 μm depending on the production modes. The results show various particle sizes, both a few nanometers and hundreds of microns. Depending on the technological modes of production, various mechanisms of the formation of powder particles can occur. Flake particles ranging in size from a few nanometers to (as a rule) one micron are obtained by the crystallization of the material vapor. They usually form agglomerates or stick to larger particles. Spherical and elliptical particles with a diameter from tens of nanometers to hundreds of microns were formed in crystallized material upon melting. The result of thermal and mechanical action during electroerosive dispersion was fragmentation grains with an average size from units to hundreds of microns. To meet the requirements for powders used in additive machines, it is necessary to select modes that exclude brittle destruction of the particles of the powder material and ensure the production of spherical or elliptical particles in the required particle size ranges. As a result of the experiment during the study of the phase composition of powders, using various technological modes and the composition of working fluids, the following phases were revealed: Cobalt (Co) with a cubic crystal lattice, a = b = c = 3.561079 Å; Chromium (Cr) with a hexagonal crystal lattice a = b = 2.738459 Å, c = 4.55078 Å; Nickel (Ni) with a hexagonal crystal lattice, a = b = 2.652590 Å, c = 4.380519 Å; sigma-Cr7Co3 (Cr7Co3 with a tetragonal crystal lattice, a = b = 8.656172 Å, c = 4.484030 Å; Cobalt Iron (CoFe), with a cubic crystal lattice, a = b = c = 2.846754 Å; Chromium Carbide (Cr3C2) with an orthorhombic crystal lattice: a = 2.821Å, b = 5.53Å and c = 11.47Å; Iron (Fe) with a cubic crystal lattice, a = b = c = 3.604293 Å; Cobalt Carbide (Co3C), with an orthorhombic crystal lattice, a = b = 4.455931 Å, c = 6.86598 Å; Cobalt Oxide (CoO) with a cubic crystal lattice a = b = c = 4.563279 Å; Magnetite (Fe3O4) with a cubic crystal lattice a = b = c = 8.4774342 Å.

Asymmetric Effective Medium Approximation for Describing the Optical Characteristics of Randomly Inhomogeneous Media with Discrete Inclusions.

The symmetric Bruggeman approximation, also known as the Effective Medium Approximation (EMA), is widely used in applications including the description of light scattering on inhomogeneous structures containing discrete inclusions. However, in the latter case, the natural asymmetry of the fillers topology, where discrete inclusions are mostly surrounded by the material of a simply connected matrix, is not taken into account. In this paper, two versions of asymmetric EMA are proposed for the case of a statistically isotropic medium containing discrete inclusions based on the difference in the structure of the fields inside and outside the inclusions. One of them does not differ too much from the usual EMA and leads to the same percolation threshold. For the second, the threshold value differs from the usual one even in the case of spherical particles. Expressions are given for the corresponding percolation thresholds in the model of randomly oriented elliptical particles. The proposed approximations are compared with the standard Maxwell Garnett and Bruggeman approximations for the case of silver particles in a dielectric matrix.

Orientational order in dense suspensions of elliptical particles in the non-Stokesian regime

Suspensions of neutrally buoyant elliptic particles are modeled in 2D using fully resolved simulations that provide two-way interaction between the particle and the fluid medium.

Inclusion of Heat Transfer on Settling Behavior of Elliptical Particles: Immersed Boundary-Thermal Lattice Boltzmann Method

In this study, the hybrid immersed boundary-thermal lattice Boltzmann method was developed and applied to assess the inclusion of heat transfer in flows containing non-circular particles. The direct forcing/heating immersed boundary method was used for determining the hydrodynamic forces and energy exchange. A complementary method was also implemented to treat non-circularity. The accuracy of the computational model and the employed complementary method were properly validated. Two cases for the falling ellipse were considered. A set of comprehensive simulations were performed and the effects of geometry, Grashof number, repulsive force, and heat transfer were analyzed. The findings of this study would be useful for a better understanding of settling non-circular particles in a thermal field.