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Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

To reduce the structural-noise level during ultrasonic testing using antenna arrays, an attempt was undertaken to implement a method for whitening echo signals with the further reconstruction of reflector images using the correlation or C-SAFT method. It is proposed to use the maximum-entropy (ME) method for reconstructing reflector images from measured echo signals. When performing numerical experiments for calculating the ultrasonic field in a medium with regions that were formed according to the principle of Voronoi diagrams, the finite-difference method in the time domain (FDTD) was used to numerically solve the vector wave equation. The attempt to use the echosignal whitening algorithm failed because of the poor conditionality of the system of linear algebraic equations, whereas the application of the ME method allowed the structural-noise level to be reduced by more than 6 dB. © 2015, Pleiades Publishing, Ltd. Source


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

To reduce the time of recording echo signals by an antenna array that operates in the double-scanning mode, it was proposed to use a set of pseudo-orthogonal coding signals. As the coding signals, it is possible to use frequency-modulated signals or phase-manipulated signals according to the Kasami code by analogy to the FDMA or CDMA techniques for multichannel communication. The use of the maximum-entropy method for decoding echo signals made it possible to reduce the noise level and increase the longitudinal resolution of reflector images in comparison to the case of using matched filtering. If an image is formed as the coherent sum of several partial images that are reconstructed using the C-SAFT method for various positions of the antenna array, it is proposed to use several sets of Kasami codes in order to additionally reduce the noise level by more than 6 dB. Numerical experiments show the efficiency of the proposed approach. © 2015, Pleiades Publishing, Ltd. Source


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

It is proposed to use the inverse C-SAFT (invC-SAFT) method to provide spatial-sensitivity equalization (SSE), which takes not only the delay times of the arrival of echo signals but also their amplitudes and phase nonuniformities into account. The invC-SAFT method reconstructs images of reflectors with a uniform scattering indicatrix in the form of reflections whose amplitudes change within ±2 dB; thus, the invC-SAFT method possesses the property of “inborn” spatial-sensitivity leveling. Numerical and model experiments at longitudinal and transverse waves confirm the efficiency of the proposed SSE method for nondirectional reflectors. © 2015, Pleiades Publishing, Ltd. Source


Bazulin E.G.,Scientific and Production Center
Russian Journal of Nondestructive Testing | Year: 2015

A modification of the combined SAFT (C-SAFT) method for reconstructing reflector images in a test object, which consists of several regions with different acoustic properties, in particular, anisotropy properties, is proposed. A method for the direct construction of a family of rays, which exit from the point where a transmitter is positioned, is used to calculate the ray trajectories with consideration for the anisotropy. After the family of rays is constructed, it is possible to analyze their attribution to a certain acoustic scheme and to approximate the calculated delays on the spatial grid of the region of iterest (ROI). This will allow one to calculate the pulse travel time from a transmitter to any point of the ROI and back to the receiver and to use the C-SAFT method for reconstructing reflector images. During processing of echo signals that were calculated in the CIVA program, the efficiency of the proposed method was demonstrated. Accounting for the anisotropy in a model experiment increased the focusing quality when reconstructing images of side-drilled holes in a specimen with a repair weld. © 2015, Pleiades Publishing, Ltd. Source


Chernov V.M.,National Research Nuclear University MEPhI | Leont'eva-Smirnova M.V.,National Research Nuclear University MEPhI | Potapenko M.M.,HIGH-TECH | Polekhina N.A.,Tomsk State University | And 4 more authors.
Technical Physics | Year: 2016

The thermophysical properties (specific heat, thermal diffusivity, thermal conductivity, linear thermal expansion coefficient, density) of 12% chromium ferritic–martensitic steels EK-181 (RUSFER-EK-181) and ChS-139 and the structure–phase transformations that occur in them upon heating and cooling in the temperature range 20–1100°C are studied. The temperatures of the start and finish of the α → γ and γ → α transformations in these steels and the Curie temperature are determined by differential scanning calorimetry. Peaks in the temperature dependence of the specific heat and jumplike changes in the linear thermal expansion coefficient and the density and the minimum of thermal diffusivity are detected in the α → γ transformation range. Specific heat peaks, thermal conductivity minima, and inflection points in thermal diffusivity curves are also observed near the Curie temperature. © 2016, Pleiades Publishing, Ltd. Source

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