Том 55, № 11 (2019)

In the ultrasonic testing of industrial facilities, it is often necessary to deal with metals having an increased level of pattern noise formed by a multitude of pulses rescattered by the structural inhomogeneities of the material. Extracting a useful signal from the pattern noise background is a nontrivial task. The fact is that the spectra and spatial distribution of pattern noise pulses and of the echo signal due to a reflector are close to each other, thus making the common methods of reducing the level of interference inapplicable. Therefore, special methods have been developed to reduce the level of pattern noise. One of such methods is the whitening (decorrelation) transformation of echo signals, originally developed for radar. This technique consists in converting correlated pattern noise pulses into white noise, which is well suppressed by conventional coherent methods such as C-SAFT, for reconstructing reflector images. In numerical experiments, echoes with pattern noise were calculated using the method of finite differences in a time domain (FDTD) when forming domains according to the rule of constructing Voronoi diagrams. As an alternative, pattern noise was calculated taking account of multiple rescattering of the probing pulse by point reflectors. It is shown that pattern noise reduction is possible when the pattern-noise correlation matrix is known with an accuracy of at least \( \approx \)10%. In model experiments, the method of whitening transformation was successfully applied to eliminate reverberation noise.

Concrete, when exposed to high temperatures, presents important changes in its properties of strength and deformation and, in extreme situations, these alterations can constitute risks to the integrity and the safety of the structures. This work presents extensive campaign with 70 cylindrical specimens and seven different mixture proportions: two of mortar and five of concrete, to analyze the propagation profile of longitudinal and transverse ultrasonic waves in concrete cylindrical specimens, associating the variation of the ultrasonic pulses with the level of compression stresses and the degree of damage imposed by high temperature. The compressive strength was within the range of 32 and 64 MPa and the specimens were exposed to temperatures of 250°, 300° and 350°C. The results indicate that longitudinal and transverse ultrasonic waves can be successfully applied in the evaluation of diffuse damage cause by uniaxial compression load and exposure to high temperatures.

We present the results of studying the effect that cyclic loading in the zero-to-tension scheme with an amplitude approximately corresponding to the conditional yield strength has on the magnetic and acoustic parameters of 08G2B hot-rolled pipe steel, including its longitudinal and transverse magnetostriction. Parameters that monotonously change with increasing the number of loading cycles are determined; this makes it possible in principle to use these parameters to develop nondestructive methods for testing the fatigue degradation of material in structures made of the investigated steel.

A method is described for measuring the relative magnetic permeability of monolithic electrically conductive annular samples in an alternating magnetic field with a frequency of 50 Hz to 5 MHz, using toroid coils wound round the samples. The reasons are indicated for the significant influence that the electrical conductivity of the samples has on the results of measurements. The proposed procedure makes use of a correction coefficient, which depends on the specific electrical conductivity of the sample and is determined from a two-dimensional calibration table obtained by finite element modeling of this measurement problem, with allowance for the deviation of the geometrical dimensions of the measured sample from the dimensions of the sample in the finite element model.

A brief list of the main directions in radiation processes using ionizing radiation in a wide range of doses and energies is given. The necessity of monitoring doses in irradiated objects and diagnosing radiation fields is substantiated. It is noted that in world practice, these problems are solved with the help of dosimetric EPR systems and detectors based on L-α-alanine. Using the example of sterilizing medical devices by radiation from an electron accelerator, a series of experimental results have been obtained that confirm the possibility of using polytetrafluoroethylene as a detector in dosimetric EPR systems for monitoring radiation processes.