On the Analytical Solution of the Kuwabara-Type Particle-in-Cell Model for the Non-Axisymmetric Spheroidal Stokes Flow via the Papkovich–Neuber Representation

Modern engineering technology often involves the physical application of heat and mass transfer. These processes are associated with the creeping motion of a relatively homogeneous swarm of small particles, where the spheroidal geometry represents the shape of the embedded particles within such aggregates. Here, the steady Stokes flow of an incompressible, viscous fluid through an assemblage of particles, at low Reynolds numbers, is studied by employing a particle-in-cell model. The mathematical formulation adopts the Kuwabara-type assumption, according to which each spheroidal particle is stationary and it is surrounded by a confocal spheroid that creates a fluid envelope, in which the Newtonian fluid moves with a constant velocity of arbitrary orientation. The boundary value problem in the fluid envelope is solved by imposing non-slip conditions on the surface of the spheroid, which is also considered as non-penetrable, while zero vorticity is assumed on the fictitious spheroidal boundary along with a uniform approaching velocity. The three-dimensional flow fields are calculated analytically for the first time, in the spheroidal geometry, by virtue of the Papkovich–Neuber representation. Through this, the velocity and the total pressure fields are provided in terms of a vector and the scalar spheroidal harmonic potentials, which enables the thorough study of the relevant physical characteristics of the flow fields. The newly obtained analytical expressions generalize to any direction with the existing results holding for the asymmetrical case, which were obtained with the aid of a stream function. These can be employed for the calculation of quantities of physical or engineering interest. Numerical implementation reveals the flow behavior within the fluid envelope for different geometrical cell characteristics and for the arbitrarily-assumed velocity field, thus reflecting the different flow/porous media situations. Sample calculations show the excellent agreement of the obtained results with those available for special geometrical cases. All of these findings demonstrate the usefulness of the proposed method and the powerfulness of the obtained analytical expansions.

Determination of changes in the mechanical properties of polymer composites with the addition of agglomerates of WC nanopowder

Recently, there has been a growing interest in the development of new composite materials with improved characteristics. The article presents the results of tests of composite specimens based on aramid fabrics modified with WC nanopowder agglomerates obtained from carbide manufacturing waste. The following mechanical characteristics were investigated: transverse bending resistance, fracture resistance and energy absorption during contact with a physical body at high speed. According to the results, the transverse bending resistance increased by 35% at a WC concentration of 5%. When 3% WC powder was added to the matrix composition, the total crack length after impact was almost halved. The largest increase in energy absorption of the samples was about 30% at 1% additive concentration. The significant increase in the investigated parameters can be explained by the complex morphology of the embedded particles. In further investigations it is planned to study in detail the mechanism of distribution of nanodispersed WC powder additive in the volume of the modified material.

TAILORING SURFACE MORPHOLOGY AND TOPOGRAPHY OF SHOT-PEENED Ti6Al4V VIA GRIT BLASTING

The present study aims to reveal the effectiveness of grit blasting when modifying the surface properties of a Ti6Al4V alloy deteriorated due to shot peening. Ti6Al4V samples shot-peened under different parameters were grit-blasted (at impingement angles of 30° and 90°, blasting pressures of 1.5 bar and 3 bar). Grit blasting proved to be an effective way of tailoring the surface topography as the surface roughness of shot-peened samples (approx. 10 µm) declined to approx. 2 µm. The surface modifications mainly occurred via micro-ploughing and micro-cutting wear mechanisms, indicating that grit blasting at 30° was more favourable than at 90° for modifying the deteriorated surface properties after shot peening. Shot-peened samples behaved similarly to mirror-polished unpeened samples during grit blasting, showing that the modified surface and subsurface properties obtained via shot peening have an insignificant effect on grit blasting of the alloy. A quantitative analysis of the area covering the embedded particles on the surface of the alloy due to grit blasting showed that the area almost doubled when the alloy was grit blasted at 90° compared to 30°, highlighting an excessive amount of embedding, which would be critical when surface decontamination is important.

Cubic microlattices embedded in nematic liquid crystals: a Landau-de Gennes study

We consider a Landau-de Gennes model for a connected cubic lattice scaffold in a nematic host, in a dilute regime. We analyse the homogenised limit for both cases in which the lattice of embedded particles presents or not cubic symmetry and then we compute the free effective energy of the composite material. In the cubic symmetry case, we impose different types of surface anchoring energy densities, such as quartic, Rapini-Papoular or more general versions, and, in this case, we show that we can tune any coefficient from the corresponding bulk potential, especially the phase transition temperature. In the case with loss of cubic symmetry, we prove similar results in which the effective free energy functional has now an additional term, which describes a change in the preferred alignment of the liquid crystal particles inside the domain. Moreover, we compute the rate of convergence for how fast the surface energies converge to the homogenised one and also for how fast the minimisers of the free energies tend to the minimiser of the homogenised free energy.

Composite Fiber Networks Based on Polycaprolactone and Bioactive Glass-Ceramics for Tissue Engineering Applications

In this work, composite fibers connected in three-dimensional porous scaffolds were fabricated by electrospinning, starting from polycaprolactone and inorganic powders synthesized by the sol-gel method. The aim was to obtain materials dedicated to the field of bone regeneration, with controllable properties of bioresorbability and bioactivity. The employed powders were nanometric and of a glass-ceramic type, a fact that constitutes the premise of a potential attachment to living tissue in the physiological environment. The morphological characterization performed on the composite materials validated both the fibrous character and oxide powder distribution within the polymer matrix. Regarding the biological evaluation, the period of immersion in simulated body fluid led to the initiation of polymer degradation and a slight mineralization of the embedded particles, while the osteoblast cells cultured in the presence of these scaffolds revealed a spatial distribution at different depths and a primary networking tendency, based on the composites’ geometrical and dimensional features.