Dissipation of energy by bulletproof aramid fabric

The bullet resistance of laminates comprised of several layers of aramid Armos fabric has been studied. The high bullet resistance of the fabric is caused by the pulling-out of yarns impacted by the bullet. The pull-out zone is cross-shaped, the centre being the impact point. The length and the width of the pull-out zone was determined for each fabric layer. Energy transferred to fibres increases with the volume of the pull-out zone. Water reduces the bullet resistance of laminates owing to reduction of the width of the zone. The length of the pull-out zone is shorter if the transverse displacement of layers is restricted. At a projectile velocity of 420 m s-1, Armos yarns do not break immediately on impact, and the longitudinal wave propagates along the fibre. Friction of yarns in aramid fabric was studied by a yarn pull-out method. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of a crack on strength of fibre-reinforced plastics

In unidirectionally reinforced composites with an elastic-plastic matrix, there is a plastic zone with lengthY ₀ proportional to the crack lengthC (Y ₀ C) at the tip of a crack. This results in a new logarithmic dependence of glass and aramid PABI fibre-reinforced plastics (FRP) on crack length and non-fulfilment of the Griffith criterion. In glass and PABI FRP without an artificial notch, defects already exist equivalent to a crack with a length depending on composite fabrication practice. In GFRP, the epoxy matrix shear yield stress grows 2.0 to 2.5 times, compared to the yield in thin films due to fibre constraint of matrix yielding. The stress distribution in front of a crack in a highly anisotropic composite with an elastic-plastic matrix is derived. The stress concentration at the tip of a crack grows with increasing matrix yield stress, resulting in a change of failure mode from accumulation of fibre breaks at low matrix strength, to brittle failure at high matrix strength. The following factors lead to composite embrittlement: (1) increase of matrix yield stress and composite shear strength; (2) decrease of temperature; (3) increase of Young's modulus of the fibre; (4) reduction of fibre strength. The dependence of aramid PPTA FRP strength on temperature exhibits a maximum. Epoxy matrix plastification leads to some increase of aramid PPTA FRP strength.     

Comparative Analysis of the Electroluminescence Efficiency in Type-I and Type-II Heterostructures Based on III–V Narrow-Gap Compounds

Semiconductors - We study in detail the mechanisms of radiative and Auger recombination in type-I and type-II heterostructures based on III–V narrow-gap materials. The presence of a...     

Inversion of the electron energy distribution in hollow-cathode glow discharge in nitrogen-sulfur hexafluoride gas mixture

The electron energy distribution function (EDF) in a hollow-cathode glow discharge in nitrogen-sulfur hexafluoride (N₂-SF₆) gas mixture has been studied by experimental and theoretical methods. On adding a small amount of SF₆ to N₂, the density of electrons in the energy interval (2−4 eV) of the EDF inversion increases by approximately one order of magnitude.     

Anti-Inflammatory Activity of Soluble Epoxide Hydrolase Inhibitors Based on Selenoureas Bearing an Adamantane Moiety

The inhibitory potency of the series of inhibitors of the soluble epoxide hydrolase (sEH) based on the selenourea moiety and containing adamantane and aromatic lipophilic groups ranges from 34.3 nM to 1.2 μM. The most active compound 5d possesses aliphatic spacers between the selenourea group and lipophilic fragments. Synthesized compounds were tested against the LPS-induced activation of primary murine macrophages. The most prominent anti-inflammatory activity, defined as a suppression of nitric oxide synthesis by LPS-stimulated macrophages, was demonstrated for compounds 4a and 5b. The cytotoxicity of the obtained substances was studied using human neuroblastoma and fibroblast cell cultures. Using these cell assays, the cytotoxic concentration for 4a was 4.7–18.4 times higher than the effective anti-inflammatory concentration. The genotoxicity and the ability to induce oxidative stress was studied using bacterial lux-biosensors. Substance 4a does not exhibit genotoxic properties, but it can cause oxidative stress at concentrations above 50 µM. Put together, the data showed the efficacy and safety of compound 4a.     

Elastic Pneumatic Cylinder for Vibration Suppression in Slip Bearings

Vibrations in machines and their effect on performance are analyzed. One of the main sources of vibrations in machine parts is the slip bearing, in which the shaft passes through a bush with some gap. Impact arises when that gap closes. The operation of vibroprotective systems based on an elastic shock absorber is considered. The influence of the rigidity of the elastic element on the performance of slip bearings is analyzed. An elastic pneumatic element of increased rigidity is proposed, in the form of a cylinder with limited radial deformation. This element is able to center the shaft relative to the geometric axis of the bearing under the action of a radial load, thanks to the difference in contact area of the external surface of the bearing housing and the surface of the elastic cylinder. A method is developed for increasing the contact of the elastic element (the pneumatic cylinder with limited radial deformation) and the surface through which the external load is transmitted, with specified bearing parameters: the cylinder length; and the excess gas pressure within the cylinder. The shaft is assumed to fit in the bearing without a gap and the cylinder casing is regarded as inextensible. The deformation and rigidity of the elastic pneumatic cylinder with limited radial deformation are found to depend on the cylinder length and the excess gas pressure within the cylinder cavity. The mathematical formulas obtained permit the determination and specification of the parameters of the pneumatic element (the cylinder length and the excess gas pressure within the cylinder) as a function of the slip bearing’s operating conditions.     

Development of a substitute for Z cast molding sand used on installations of 3D printing for obtaining aluminum,magnesium, and iron casting

The goal of this work was to develop substitutes for the ZCast molding sand for production molds and rods by 3D printing in Z Corporation installations (United States). The composition of a substitute for the ZCast 501 powder with the application of the gypsum binder and the composition of a substitute for the Zb56 proprietary binder were developed. They do not copy the composition of proprietary consumables, but they ensure the acquisition of molds similar in quality. Using these molds, casts were fabricated from magnesium and aluminum alloys and the possibility to obtain casts from copper alloys and cast iron was shown.