Numerical simulations and experimental study of frequency-dependent dielectric properties of composite material with stochastic structure

Results of a computer modeling and analytical estimations of frequency-dependent dielectric properties of a composite material with stochastic structure in the frequency range from 1 mHz to 1 kHz are presented and are compared with experimentally obtained parameters. The studied composite was a mixture of materials having considerably different properties, where the inclusion phase with the volume fraction of 0.31 was distributed randomly in the host material forming a complex three-dimensional structure. For such composite dielectric, the applicability of bounds on the effective complex permittivity and different known mixing formulas for estimating of the effective parameters is examined. The numerical simulations performed using measured frequency-dependent characteristics of the constituents and the reconstructed three-dimensional stochastic structure of the composite, yielded values of the effective dielectric permittivity which were in good agreement with the measured ones. Frequency variations of the computed distributions of the microscale electric field and energy losses in the bulk of the studied composite dielectric are presented and discussed.     

Equivalent surface impedance of an infinite array of slot impedance loads designed on the basis of coupled rectangular domains

A 2D design of an infinite array of slot impedance loads (SILs) is considered. Each SIL is designed from two coupled rectangular domains connected through apertures with both each other and free space. The integral equation method is used for determination of the equivalent surface impedance (ESI). Dependences of the ESI value are investigated for different geometric dimensions to wavelength ratios. It is shown that the SILs under study can be used to obtain a reactive component of ESI having either positive or negative sign for the thickness of the impedance structure not exceeding one-quarter the wavelength.     

Investigation of the reaction products of unsymmetrical dimethylhydrazine with potassium permanganate by gas chromatography-mass spectrometry

The gas chromatography-mass spectrometry technique was used to investigate the composition of the reaction products of unsymmetrical dimethylhydrazine with a potassium permanganate and potassium permanganate-hydrogen peroxide mixture. If the water contamination level is within 50 threshold limit values (TLV) (1 mg/ml), the proposed detoxication method utilizing potassium permanganate in combination with hydrogen peroxide allows for the reduction of the UDMH concentration to a safe level without the accumulation of transformation products. The detoxication of aqueous solutions with significant UDMH concentrations (up to 50000 TLV) (1 g/l) with potassium permanganate alone or in combination with hydrogen peroxide reduces the UDMH concentration to a safe level, but UDMH transformation products, including the extremely toxic nitrozodimethylamine, are accumulated in the solution.     

The structure and properties of forged composite high-speed steel: Titanium carbide

The structure of a powder composite (carbide steel) based on high-speed steel with dispersed inclusions of titanium carbide and obtained by forging powdered billets is investigated. The elemental and chemical composition of the material is determined. The physicomechanical properties of the forged carbide steels obtained are compared with those obtained by other methods.     

Computer modeling of interaction of gas discharge plasma with solid dielectric barriers

A computer model describing charge transfer in a system consisting of two parallel-plate metallic electrodes covered with solid dielectric barriers immersed in gas medium is proposed. The material of the barriers is supposed to be a non-ideal insulator whose properties correspond to polyethylene and air is considered as a gas phase. The model is based on continuity equations for fluxes of charge carriers and accounts for their drift and diffusion and also for different sources of their generation and losses in different media. The continuity equations are coupled with Poisson's equation for computing electric fields affected by temporal and spatial variations of space charges in the system. Results of the computer simulations are obtained for the case when the applied field in the gas exceeds its breakdown threshold, i.e. charge transfer in the gas phase takes place in the form of an electrical discharge (electron avalanche and streamer). Evolution of generated discharge plasma is analyzed taking into account conditions on gas-solid interfaces and in the bulk of the solid dielectric barriers.     

Parameters and micromechanisms of fatigue crack growth in sheet magnesium alloy samples

Growth rates of part-through and through fatigue cracks have been measured for two magnesium alloys — MA12 and IMV6 — and the micromechanisms of fatigue fracture were studied at all stages of growth. Conclusions about the peculiarities of the kinetics and micromechanisms of part-through and through crack growth, depending on the applied stress amplitudes and alloy structure, are made from a comparison of the results obtained.     

Computation of Parameters of Power Transformer Windings for Use in Frequency Response Analysis

We present a 3-D model for calculating magnetic fields in a power transformer and the effective parameters (inductance and resistance) of its windings. The transformer is representative of large transformers with power ratings ranging from hundreds of kilovolt amperes to hundreds of megavolt amperes. The model accounts for anisotropic frequency-dependent properties of the laminated transformer core and eddy currents in the steel sheets. We discuss the results of the calculations performed in the frequency range 10 Hz-10 MHz, and show that the largest variations of both the magnetic field and parameters of the windings take place at frequencies below ~10 kHz and, at frequencies higher than 1 MHz, the magnetic core does not significantly affect the variation of the effective parameters     

The quality of hot-stamped powder carbide steel

The quality of hot-stamped powder carbide steel is considered within a comprehensive approach to the development of its production technology. Means are outlined for ensuring satisfactory quality of such steel in its production.