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No 8 (2023)
Articles
Ultrasonic adhesion control of special coatings
Abstract
Quality control of coatings is an urgent task. Of interest is not only the detection of a defect in the coating in the form of detachment from the substrate or delamination between layers of a multilayer coating, but also the detection of the place of probable defect formation in the form of a site with reduced adhesion. The purpose of this work is to substantiate the possibility of using the reflected radiation method (echo method) of an acoustic type of non-destructive testing with optical-acoustic generation of acoustic vibrations to assess the adhesion between the coating layers and between the coating and the substrate. The objective of this work is to establish a correlation between the acoustic characteristics of coatings and the tear strength of coatings. The relevance of the work is emphasized by the lack of methods and means of non-destructive testing of adhesion of coatings with proven effectiveness and reliability to date. In order to achieve this goal, coating samples with embedded artificial defects were developed and manufactured. A correlation was established between the acoustic characteristics of the coating and the tear-off strength of the coating, confirmed as a result of mechanical tests, which emphasizes the scientific novelty of the research.
Defektoskopiâ. 2023;(8):3-10
3-10
Digital equipment and algorithms for determining the basic parameters of piezoelectric elements in pulsed excitation mode
Abstract
A method for measuring the spectrum of complex admittance of piezoelectric elements in the pulsed excitation mode and its digital implementation is proposed. The method reduces the duration of measurements, and the processing algorithm increases the accuracy of the estimated parameters. To determine the characteristic frequencies, Q-factor and parallel capacitance, an algorithm of fractional-rational approximation of the frequency dependence of the complex admittance in the resonant frequency range is used.
Defektoskopiâ. 2023;(8):11-20
11-20
Density study of thermoexpanded graphite samples by acoustic amplitude-shadow method
Abstract
The paper presents the results of the study of sensitivity of the acoustic method of density control for samples of expanded graphite based on registration of changes in the amplitude of the signal passed through the sample due to density changes. The results have shown that the limiting sensitivity of the method is commensurable with an error of density measurement by direct weight method and mass and equal to 26 kg/m3 and 0.02 g. The unevenness of the density distribution over the area of TEG samples of different thickness was evaluated, and the amplitude excursion of the signal transmitted through the sample, proportional to the density deviation, for some sheets reached up to 50%, for mats - 30%, and the smallest did not exceed 10%. In the process of scanning, an inversely proportional dependence of the amplitude of the passed acoustic signal on the average density of the samples was revealed, which is most expressed for small thicknesses of TEG mats and sheets.
Defektoskopiâ. 2023;(8):21-31
21-31
Detection of echo signals from discontinuities due to the use of super-resolution procedures for the control of concrete piles by the impact method
Abstract
To control concrete piles, an impact method is used, which allows recording echo signals from the sole of the pile and from reflectors in it. However, the resolution of the measured echo signal is not high enough to confidently separate the reflected pulses and determine their phase. The use of the maximum entropy (ME) method allowed to increase the resolution of the echo signals obtained by the impact method in a concrete pile with a length of 3000 mm by about three times and confidently identify echo signals from artificial reflectors, both in the form of a disk with a thickness of 100 mm and in the form of a parallelepiped with a height of 300 mm. The use of the method of Compressive Sensing (CS) made it possible to increase the resolution of the same echo signals by about ten times. The main problem of the successful application of the ME and CS methods is the determination of the impulse response of a concrete pile upon impact. A method for estimating the pulse response from the processed echo signal is proposed.
Defektoskopiâ. 2023;(8):32-39
32-39
Low-velocity impact damage detection in cfrp laminates based on ultrasonic phased-array ndt technique
Abstract
To investigate the delamination characteristics of CFRP laminates in Barely Visible Impact Damage (BVID) state, Low-Velocity Impact Tests (LVIT) and Non-Destructive Testing (NDT) were employed. The energy thresholds of six diverse ply-stacking sequences of laminates in the BVID state were established utilizing visual inspection and contact measurement methods. Ultrasonic phased-array NDT techniques were employed to evaluate quantitatively the magnitude of delamination damage from different viewpoints, including delamination area, shape, and trend variation. Furthermore, the impact resistance of laminates was qualitatively evaluated by analyzing the distinctive delamination damage forms of various specimens to identify the effects of the ply-stacking sequence. The findings of this study demonstrate that reducing the angle disparity between adjacent plies and minimizing the repetition of identical plies can mitigate delamination damage. Additionally, enhancing the ratio of ±45 and 0° plies can improve the flexural stiffness of the structure. Specifically, the ultrasonic phased-array NDT technique was shown to effectively detect delamination damage within the laminate in the BVID state.
Defektoskopiâ. 2023;(8):40-49
40-49
A circular eddy current probe using miniature fluxgates for multi-orientation slit evaluation in steel components
Abstract
Detection of crack propagation, such as its direction and depth, is one of the important aspects in ensuring the safety and reliability of steel structures. This study presents a development of a circular eddy current excitation probe using a planar differential miniature fluxgate to detect vertical and horizontal slits. The probe utilizes a circular eddy current excitation technique that induces multi-direction eddy currents in a mild steel plate and a sensing configuration based on the tangential magnetic response. The performances of the developed probe were characterized based on line and 2-D map scans of the magnetic response due to the induced eddy currents in mild-steel samples from different orientations and depths of artificial slits. The results showed that the developed probe obtained a signal correlation with the slit depth at different slit orientations. The vertical and horizontal slits were able to be visualized from the magnetic field distribution, where the differential imaginary component had a better detection sensitivity for the vertical slits represented by the measured peak-to-peak signals. The detection of multi-orientation slits revealed that the slit orientation could be estimated from the magnetic response maps with a detection limit of 5 mm in the slit length and 0.5 mm in the slit width, respectively.
Defektoskopiâ. 2023;(8):50-61
50-61
Increasing the structural sensitivity of the residual magnetization and coercive force of steels
Abstract
The statistical analysis of measurement results of residual magnetization Mr and magnetization Ms of technical saturation of structural steels shows that ratio KS = Мr/Мs is much less sensitive to changes in phase composition of steels than Mr. Taking into account and more precise measurement of KS than Mr, it is offered to use the parameter KS for magnetic structuroscopy of medium-carbon steels in practically important range of variation of tempering temperature instead of Mr and coercive force Нс. It is shown, that the magnetic parameter ξ = Нс /Мs , at heat treatments, changing phase composition and structure of steels, in some cases has less sensitivity, than parameter Нс, to the phase composition of steel. To improve the reliability of interpolation by analytical function of the experimental dependence between the magnetic parameter and steel hardness, it is proposed to use a logical function "if" - different functional dependence between the magnetic parameter and steel hardness, depending on the measured value of the magnetic parameter.
Defektoskopiâ. 2023;(8):62-64
62-64
On the possibility of determining the elastic modulus of metals by the dynamic instrumented indentation method
Abstract
The study was carried out as part of the development of a non-destructive method for measuring the mechanical properties of metals and alloys based on the dynamic instrumented indentation method. The purpose of this work is to study the possibility of measuring the modulus of elasticity using a modified Leeb hardness tester. The experiment was carried out on samples of 20X25H20C2, 20X23H18, BpA9Zh4H4Mts1 alloys.
Defektoskopiâ. 2023;(8):65-67
65-67
Comparative analysis of acoustic anisotropy of pipes and sheets using SH- and tH-waves
Abstract
The results of comparative studies of acoustic anisotropy of tH-waves and SH-waves in plates and tubes of different thickness are presented. Turning of polarization direction due to the corresponding orientation of transducers allowed to estimate the angular indicatrix of wave velocity relatively to the rolling direction. Significant differences in acoustic anisotropy of tH-waves and SH-waves are shown for both tubes and sheets.
Defektoskopiâ. 2023;(8):68-70
68-70
The structure perfection studies of LiCaAlF6 crystals by laser acoustics technique
Abstract
The acoustic properties of LiCaAlF6 crystals and the annealing procedure impact on them were studied. The velocities of longitudinal and shear ultrasonic waves along the direction of the optical c-axis of the crystals were measured by laser acoustics, and the mechanical constants were determined: modules of elasticity, all-round compression, shear, and Poisson's ratio. It has been established that the attenuation coefficient of ultrasonic waves in the 1-15 MHz frequency range can serve as a characteristic of the optical perfection of the crystals. The effect of ultrasonic annealing of LiCaAlF6 crystal samples under prolonged exposure by pulsed ultrasound was discovered.
Defektoskopiâ. 2023;(8):71-73
71-73