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The effect of transformation of focused ultrasound radiation into collimated beams of longitudinal and transverse waves in the volume of a hemispherical transformer after refraction on its surface has been described. When the hemisphere is fastened on a studied plane–parallel object, the formed sharp beams of elastic waves incident normally on the surface of the sample make it possible to perform elastic measurements with minimum errors, which can be due to refractive aberrations of the focused beam.

Ensuring reliable operation of power transformers as part of electric power facilities is assigned to the maintenance and repair system, whose important components are diagnostics and monitoring of the technical condition. Monitoring allows you to answer the question of whether the transformer abnormalities and how to do they manifest, while diagnostics allow determining the nature, the severity of the problem, determine the cause and possible consequences. The article presents the results of the author’s research on creating an algorithm for adaptive control of the technical condition of power transformers using diagnostic and monitoring data. The developed algorithm implements the decision-making procedure for ensuring the reliable operation of oil-filled transformer equipment as part of the substations of electric power facilities. The decision-making procedure is based on the method of statistical Bayesian identification the states of a transformer based on the results of dissolved gas analysis (DGA) in oil. The method is characterized by high reliability of recognizing defects in the transformer and the ability to adapt the probabilities of the obtained solutions to the newly received diagnostic information. These results illustrate the effectiveness of the developed approach and the possibility of its application in the operation of oil-filled transformer equipment.

We studied biocompatibility and bioresorption of 3D-printed polylactide and polyglycolide tissue membranes. Ultrasound microscopy and histological examination showed that membranes fabricated of a copolymer of lactic and glycolic acids in a mass ratio of 1:9 are bioresorbed and have good biocompatibility with soft tissues (connective tissue, adipose tissue, and epithelium). An important feature of the copolymer membranes, which differs them from pure polylactide membranes, is the formation of a thin fibrous capsule that did not interfere its destruction by the mechanism of hydrolytic resorption.

This paper presents an approach to the generalization of the features of solid propellant combustion in gas generators of propulsion systems based on a one-dimensional differential model. The heat release rate function represented by mutually orthogonal Laguerre polynomials in the differential model is identified by solving the inverse problem of combustion theory and using measured gas parameters in the gas generator. This makes it possible to establish the relationship between the solid propellant combustion features and the gas generator operating modes and formulate boundary conditions for numerical investigation of the solid propellant gas generator.

A new non-destructive express method for assessing the authenticity of numismatic material is considered in the paper. Non-destructive methods of pulsed acoustic microscopy in the frequency range of 50-100 MHz were applied. Samples of silver coins dated 1924 and 1979 were examined. The characteristic values of the longitudinal and transverse sonic velocity of the samples were obtained. The method of hydrostatic weighing was used to measure the density of the metal. It was shown that assessment of the authenticity and the safety degree of coins can also be carried out by revealing the internal defects such as corrosion. Acoustic visualization in the reflection mode allows imaging the offset of the obverse relative to the reverse and to determine the centre of the coin deviation, which also confirms the quality of the minting.

This paper is devoted to the evaluation of composite materials and components using ultrasonic visualization of structural changes caused by the external force. It is proposed to measure the strain of a sample under load using digital correlation of images recorded by a scanning acoustic microscope. An algorithm for processing the spatio-temporal ultrasonic data is developed to measure the longitudinal and transverse strains versus the applied force. The four-layer carbon fiber-reinforced composites with alternating packing of fibers (90/45) are evaluated by the proposed method. The relationships between the strains and the applied force are obtained up to the destruction of the sample. It is shown that the maximal longitudinal and transverse strains achieved for the test sample are 1.2% and 0.3%, respectively.

The paper shows the experience of using scanning pulsed acoustic microscopy (SIAM) to solve practical problems of quality control of polymer composite materials (PCM), to identify flaws and in-service damage, and to study changes in their internal microstructure under external influences. Acoustic images of structural defects and damages typical for carbon fiber reinforced composites are presented.

It is found that a ceramic based on zirconia modified with oxides of yttrium and ytterbium (Yb–TZP) maintains high mechanical properties after hydrothermal treatment, equivalent to 20 years of residence of an implant in vivo. The study of the surface of ceramic samples before and after hydrothermal treatment by atomic force microscopy is carried out. The change in the grain composition of the microstructure of this ceramic is shown, defined by subsurface change in the phase composition caused by martensitic transformation of zirconia.

The vortical mixing concept in the ramjet channel is analyzed. The results of simulating the gasodynamic scheme permit the concept of increasing efficiency for ramjet operation to be substantiated.

Results of life firing tests of a dual-mode ramjet engine intended for operation in the speed range М = 3−6 are discussed. The tests were carried out on a test bench under freestream conditions typical of Mach 6 flight at 27.6-km altitude. In the tests, the adopted design and technological solutions were verified, and efficient operation of the ramjet engine with kerosene combustion during 110 s was demonstrated.

A method of increasing the efficiency of mixing in an air-breathing rocket engine is discussed. Three-dimensional simulations confirm the advantages of the proposed method based on using normal supply of products of incomplete combustion of a pasty propellant into the wake zone behind a bluff body in an air flow.

Basic relations of the concrete deformation model based on the modified theory of flow are presented. Calculation data are compared with experimental results in tension, compression, and compression–tension. The error of experimental data approximation is estimated on the basis of the proposed relations.

The process of combustion of a hydrocarbon fuel in a pulsed mode is discussed on the basis of results of ramjet testing in an external flow modeling a Mach 5 flight.

The fluorescence decay constant of a fluorescent polymer optical fiber is measured by two different side illumination methods. Comparative analysis of these methods is performed. It is shown that the difference in the measured parameters is caused by different conditions of energy exchange between the core, cladding, and radiation modes of the fiber waveguide.

The paper introduces the methods with time-resolved technique and isosurface display technique to get two- and three-dimensional (3D) acoustical imaging for scanning acoustic microscopy. Time-resolved technique presents the way to realize two-dimensional (2D) acoustical imaging - A- (O-), B- and C-scan, and a discrete combinatorial 3D image; and isosurface display technique realizes a 3D image with continuous distribution in full direction. The paper proposals a transitional model of square column, which consists of the data of echo signal pattern extracted from volume database, to construct the imaging cube and depict an isosurface using isovalue of internal boundaries in the cube, for the evaluation of internal defects in bulk specimen - Boron Nitride. 3D acoustical imaging has the advantage to show the position, size, appearance, distribution, and tendency of internal structures (voids, inclusions and defects) with complex shapes in non-transparent bulk material. The results show that 3D acoustical visualization presents more affluent, overall and intuitive pattern than 2D imaging for micro-sized structure investigation.

This paper discusses an approach to implementing the operation and designing the flow duct of a ramjet combustor. Methods of air compression, ignition, flame stabilization, and fuel combustion in the flow are considered for the purpose of implementing an effective process on a short length with moderate total pressure losses. Advantages of narrow-mode ramjet engines are noted. Comparative results of experiments on the burning of hydrocarbon fuels in the ramjet combustors are given.

The IR spectra in the hydroxyl group stretching vibration region of the simplest hydroxyalkylpyrrolizidines have been examined. The spectra were taken in the form of pure liquids, dilute solutions in carbon tetrachloride, and for individual bases in the gas phase. It was shown that in dilute solutions ΔνOH depends on the geometric parameters of the intramolecular hydrogen bond (IMHB). The energy of the IMHB of 3-(2-hydroxyethyl)pyrrolizidine was measured in dilute solution and in the gas phase.

Non-destructive inspection of carbon-fiber-reinforced (CFR) composites applied in aerospace industry attracts a wide attention. In the paper, high frequency focused ultrasound (50-100 MHz) has been applied to study the bulk microstructure of the CFR material and mechanisms of its destruction under the mechanical loading. It has been shown impulse acoustic microscopy provides detecting the areas of adhesion loss at millimeter and micron level. Behavior of the CFR laminate structure fabricated by prepreg or infusion technology has been investigated under the tensile and impact loading.

It is well known that many porous media such as rocks have heterogeneities at nearly all scales. We applied Biot's poroelastic theory to study the propagation of elastic waves in isotropic porous matrix with spherical inclusions. It is assumed that the heterogeneity dimension exceeds significantly the pore size. Modified boundary conditions on poroelastic interface are used to take into account the surface tension effects. The effective wavenumber is calculated using the Waterman and Truell multiple scattering theory, which relates the effective wave number to the amplitude of the wave field scattered by a single inclusion. The calculations were performed for a medium containing fluid-filled cavities or porous inclusions contrasting in saturating fluid elastic properties. The results obtained show that when we consider elastic wave propagation in poroelastic medium containing soft inclusions, it is necessary to take into account the capillary pressure. The influence of the surface tension depends on the d...

The correct description of the macroscopic (overall) physical properties of micro-inhomogeneous (composite) materials by micro-mechanics methods (the self-consistent schemes, for example) requires information about the microstructure and texture of such materials. Often, such information (of shapes inhomogeneities and peculiarities of their spatial distribution) is not available. In this paper, we suggest a method of calculation of the characteristics of micro-inhomogeneous materials that could be applied to a wide class of isotropic materials. This method assumes the absence of a closed order in the material microstructure (a 'perfectly disordered' (PD) medium). We used the PD approximation to predict the effective thermo- and poroelastic, electric and thermal properties of micro-inhomogeneous media.The expressions for the effective characteristics obtained by this method are always inside of the Hashin–Shtrikman universal bounds. For a two-phase material with fluid component, the effective bulk module satisfies Gassmann's relation for fluid-filled porous media and generalizes such a relation to inhomogeneous thermoelastic and poroelastic media. A comparison of the theoretical results with available experimental data shows a satisfactory coincidence even in the case of high contrast of the component properties.The simplicity of the numerical realization of the method makes it attractive for applications in the absence of detailed information about the material's microstructure.

This paper is dedicated to studying crazing under cyclic bending with axial loading. The tests were carried out on a special testing equipment. The influence of such factors as the bending radius, the axial load, and the number of bending cycles was investigated. The concentration of crazes was determined by optical microscopy. Moreover, the optical properties of POFs were studied by means of optical spectroscopy and light scattering . As a result, the dependences of craze concentration on the bending radius, axial load, and the number of bending cycles were obtained. The magnitude of irreversible changes was shown to be proportional to the density of the crazes nucleated upon deformation of the light guides.

Explicit expressions for the effective pyroelectric, dielectric, piezoelectric, elastic and thermoelastic constants of a matrix composite have been obtained in closed form. A numerical analysis has been carried out of the concentration dependences of constants of a composite in which the BaTiO3 ceramics is the matrix while the inclusions are represented by spheroidal ceramic particles of PZT-19. A case is examined when the matrix and the inclusions possess opposite polarization. At a certain concentration of PZT-19 the composite exhibits well pronounced pyroelectric properties without having any appreciable piezoeffect. At another concentration, it manifests marked piezoelectric properties, but does not possess the pyroeffect. Practical implementations of the results are discussed.

The paper represents a general and comparative (for particular examples) critical analyses of designing the cathodic protection for branched gas-distribution city systems, proceeding from an average protection current density, its experimental values, or the equations for the linear pipe sections. The limitations of such approaches are revealed, yet the protection current values thus rated can reasonably be used for estimating the current leakage from a gas-distribution system to extraneous underground structures.

Application of dye-doped polymer optical fiber used for conversion of the pulse coherent in the incoherent radiation for the creation of the illuminator to the microscope is described. The technical requirements to the fiber are determined. The manufacturing technology of the fiber and the experimental setup are describes. Experimentally measured the contrast speckles. The images of microscopic moving particles are present.

The changes in the permeability of a porous medium resulting from the reorientation of the solid matrix particles under the influence of the percolating flow are considered. The mathematical model also contains the angular momentum equation, including the moment of the viscous flow forces. The state of the elastic matrix is characterized not only by the repacking strains but also by the particle orientation vector. The latter determines the anisotropy of the permeability tensor. The effective stress, strain, pore pressure and orientation vector fields in the neighborhood of an operating well are constructed. The effect of the induced permeability anisotropy on well productivity is noted.

The structure and functioning features of a microprocessor system for controlling the geometrical dimensions of a polymeric optical fibre in processes of spinning and heat-stretching in a complex technological assembly have been described.

The form of the interface of polymer melts in bilaminar streams during flow in spinneret channels has been studied on a batch laboratory industrial set-up. Numerical calculations of the coordinates of the interface in bilaminar streams have been carried out using the previously proposed mathematical model. The results of experimental studies agree well with theoretical calculations, which indicates the adequacy of the theoretical model for a real process.

One of the stages of producing multilayer films and two-component fibers (including optical fibers) is joint extrusion of two or more molten polymers through a forming channel. Here there is layered or stratified flow [i]. Areas of steady-state stratified flow are the most completely studied where the profile of the flow rate and the position of the interface of the liquid layers is unchanged over the length of the channel [1-4]. Fewer works are devoted to studying the initial area of combined flow where, as is shown in an experiment in [5] and in theoretical finite element analysis [6], the coordinates of the interface vary considerably.

The quality of the natural vibrations of specific bacteria is investigated using a shell model which accounts for the elastic properties of the membrane and the associated viscosities of the cytoplasma and the surrounding fluid. The motion of the membrane is approximated in terms of the distribution of internal forces over the shell thickness, which is assumed to be much less than the size of the cell. Flexural moments and intersecting stresses are neglected. Using experimentally obtained values for the membrane properties, high-quality resonances are predicted for several types of bacteria which have radii greater than 5 microm. Viscous shear waves are the main source of energy dissipation as has been previously reported in other studies on the natural oscillations of red blood cells, drops, and bubbles. Implications for the acoustic mediated destruction of bacteria are discussed.

Elastic properties of bulk metallic glass (BMG) Pd39Ni10Cu10P21 have been studied basing on sonic velocity data analysis. Different states of the Pd39Ni 10Cu 1 oP21 system (glassy state, super-cooled liquid (SCL) and re-crystallized states) were obtained by annealing of the samples at different temperature near the glass transition and onset crystallization temperature. Microacoustical technique has been applied to measure local values of longitudinal and transverse elastic wave velocities and their distribution over a specimen body. Finally sonic velocities CL and CT, density p, bulk K and shear G elastic moduli were measured for different states of Pd39Ni 10Cu 10P21 BMG. It has been shown decreasing values of p, CL and K as temperature. For the re-crystallized state ultrasonic measurements were performed by low-frequency flat transducer because of high ultrasonic attenuation in this case. Acoustic images (C-scans) evidence occurrence of rough-grain microstructure at this state. It is assumed the rough granular structure with particles size 70-80m is characteristic for re-crystallized state of BMG.

The solution of the inhomogeneous Helmholtz equation (the ’dynamic’ or ’Helm- holtz potential’) and its time domain representation (the retarded potentials) for an ellipsoidal source region is analyzed. They occur in many dynamic problems of mathematical physics such as wave propagation and scattering phenomena. From an aesthetic and practical point of view 1 D-integral representations for dy- namic potentials are highly desirable. So far such representations seem to be absent in the literature. Here we close this gap for the internal dynamic potential of an ellipsoidal shell. The solution of the external space can be constructed by applying Ivory’s theorem. Moreover we construct surface integral represen- tations for inhomogeneous ellipsoidal sources for source densities of the form\( \rho = \Theta \left( {1 - P} \right)f\left( {{P^2}} \right),\left( {{P^2} = \frac{{{x^2}}}{{a_1^2}} + \frac{{{y^2}}}{{a_2^2}} + \frac{{{z^2}}}{{a_3^2}}} \right) \) . Closed form solutions are found 2 ). for the retarded potentials of inhomogeneous spherical sources. In the static limit the dynamic potentials coincide with well known classical results for the Newtonian potentials of ellipsoids of Dyson [4] and Ferrers [6].

The focused ultrasonic beam technique has been employed to image bulk microstructure of carbon fiber-reinforced (CFR) composites. Ultrashort probe pulse (operation frequency of 50 MHz) provides layer-by-layer visualization with in-depth resolution of 100 µm. At such frequencies the ultrasonic wavelength 60 µm) becomes smaller than characteristic sizes of many structural components in CRF. The composites are perceived by elastic waves as a system of numerous reflectors. Echo signals reflected from large-sized structural units (plies, fiber bundles and etc.) and microdefects have been used to visualize bulk microstructure of these materials.