Russian Journal of Nondestructive Testing最新文献

The paper describes a practically implemented method for correcting the geometrical aberrations introduced by a scanning device as a proposed stage of the computer radiography system qualification. The presence of geometrical distortions in the scanned images affects the metrological characteristics of the measurement methods and techniques that are using these systems. The method allows for correction of a systematic error obtained when scanning photostimulable phosphor detectors on the digital radiography devices. The main stages of method implementation include fabrication of the calibration sample, conducting reference instrumental measurements, comparing reference measurements with digital image processing results, and estimating and correcting the errors. During the period 2022 to 2024, the examination results for three scanning devices were analyzed. The use of the geometrical aberration correction method allows for minimization of distortions as well as estimation of quality and stability of scanning devices.

During the service period, pipelines are prone to various factors causing damages such as holes and cracks. This paper takes 20# steel pipelines as the research object, setting time-domain amplitude, spectral amplitude and power spectral density as quantitative indicators, to study the response characteristics of the longitudinal mode of guided waves to different damages under different excitation frequencies, explore the sensitivity of the longitudinal mode of guided waves to pipeline damages and analyze the applicable excitation frequencies. The results show that the longitudinal mode of the guided wave is most sensitive to circumferential cracks, and has the weakest sensitivity to longitudinal cracks. Therefore, it is not applicable for the detection of longitudinal crack damage. Furthermore, the longitudinal guided wave mode excited at 70 and 90 kHz exhibits high sensitivity to pipeline damage, making it well-suited for its detection. The frequency selection method proposed in this study, which is based on multi-index comparison, shows broad applicability and serves as a valuable reference for the detection of damage in pipeline structures.

The article considers numerical modeling of the method of defect localization in the three-dimensional (3D) structures based on acoustic-electrical conversions. It is shown that this method allows calculating the location of defects based on the parameters of the electromagnetic response to a deterministic pulsed acoustic excitation at selected points on the surface of the tested solid sample. To test the developed modeling method, two finite element models were built: single-layer and two-layer three-dimensional structures. The results of calculations using these models confirm the efficiency of the acoustic-electrical conversion method in localizing defects in three-dimensional heterogeneous solid structures.

In the field of industrial nondestructive testing (NDT), the accurate acquisition of three-dimensional (3D) shape measurement is crucial for defect identification and structural assessment. As an important branch of 3D shape measurement techniques, laser scanning technology plays a key role in machine vision due to its high precision and noncontact nature. In laser scanning technology, the accuracy of 3D coordinate calculation depends on rapid high-precision extraction of laser stripe centerlines. To address this, this paper proposes a grayscale-curvature constrained algorithm to enhance the speed and accuracy of laser stripe centerline extraction. The process employs median filtering and improved anisotropic gaussian filtering (IAGF) for noise suppression. An energy function combining grayscale and curvature information is then defined. For each image row, the pixel minimizing this energy function is selected as the center candidate. Finally, subpixel refinement is performed along the normal direction based on the gradient-tangent orthogonality principle. Experimental results demonstrate that IAGF reduces centerline extraction error by 28.7% compared to standard gaussian filtering. Furthermore, the proposed algorithm significantly outperforms the grayscale centroid, normal-based grayscale centroid, and conventional Steger methods, showing accuracy improvements of 58.3, 46.2, and 35.4% respectively. The reconstructed dimensions of a gauge block exhibit minimal relative errors, specifically only 0.04% for length, 0.07% for width, and 0.17% for thickness. The proposed algorithm enhances 3D shape measurement precision, which can be effectively applied in the field of NDT industrial applications.

Selecting a proper method for inspecting particular materials is an imperative challenge in the nondestructive testing (NDT) field. In this regard, comparing different techniques to reach the best defect detection efficiency is of great importance. Digital shearography and active thermography are among the new NDT techniques providing many advantages such as full-field, noncontact, accurate and high-speed inspection. In this paper, both methods are employed to be compared in the detection of subsurface defects in carbon fiber-reinforced plastics (CFRPs). In this respect, several CFRP specimens with artificial defects, including delamination and cracks with various depths and sizes, were prepared. After conducting the relevant experiments, the results revealed that both methods are efficient in NDT of CFRPs. Nevertheless, active thermography indicated superior performance in the inspection of delamination by detecting deeper defects. Shearography showed a better performance in the case of cracks and short defects. However, shearography required more test preparation and a longer heating time.

It is noted that manufacturers and suppliers of ultrasonic flaw detectors usually focus on the ultimate sensitivity of the equipment but pay little attention to the error that the linear dimensions of defects can be measured with. It is also noted that the physical principles underlying ultrasonic flaw detection and the accumulated practical experience of its application show that currently, defect sizes can be measured no more accurately than with an error of 1 mm. Therefore, it would be more accurate to talk not about measuring the height of defects in the cross section of welded seams but about estimating this height using ultrasonic flaw detection methods. Examples of representing sections with defects in the form of acoustic B-scans are provided, and it is shown that these images have changed little over the past 60 years, despite the fact that signal processing techniques and technology have developed significantly during this time. At the same time, the article shows that it is possible to qualitatively assess the change in defect height by fractions of a millimeter. In this regard, the results of calculation and experiment on assessing the influence of weak material anisotropy on the shape of the phase spectra of bottom pulses are presented, and it is shown that, in addition to the traditionally used time sweeps of signals (A-scans) and amplitude spectra, it is advisable to pay more attention to the analysis of phase spectra of signals received from products. Phase spectra change significantly more than other characteristics of the recorded pulses also when the height of defects in the cross section of a welded seam increases. This conclusion also applies to cases where the defect height does not exceed the length of the used ultrasonic waves.

A brief analysis of publications addressing the influence of acoustic coupling on signals recorded during ultrasonic testing of components and welded joints is provided. It is noted that most often the authors pay attention to the amplitudes of pulses, but do not analyze their spectrum and its alteration in relation to the quality of preparation of contact surfaces. Experimental studies of backwall echoes received from carbon and austenitic steel specimens have demonstrated that variations in surface roughness (within the range of Rz 10 to Rz 80 μm) not only alter the amplitude of the detected signals but also cause significant distortions in their waveform and spectral composition. In some cases, the operational frequency of the backwall signal may decrease by 30% or more relative to the nominal frequency of the piezoelectric transducer. Measurements performed on specimens with both deterministic and stochastic surface roughness profiles have shown that the quality of the coupling surface preparation has a substantially greater impact on the spectral characteristics of the received signals compared to the backwall surface roughness. The findings highlight the necessity of accounting for the influence of coupling surface roughness in test objects and welded joints on the spectral content of ultrasonic signals when developing procedural guidelines for pulse–echo and diffraction-based ultrasonic testing methods.

In environments with high temperatures and pressures, heavy-duty gas turbine blades run over extended periods of time. The long-term action of complex mechanical loads and thermal stresses, which can change material properties and cause fatigue fractures in components, directly affects the service life and safety of gas turbines. Turbine blade failure may result from these fissures. Laser ultrasonic has shown particularly encouraging results in high-temperature and in-service detection of fatigue microcracks in heavy-duty gas turbine blades. The ultrasonic signal utilized in laser ultrasonic testing links the material’s microstructure qualities with microcrack defects due to the uneven microstructure of turbine blades, which results in insufficient detection accuracy. This paper proposes a dual-probe laser ultrasonic testing method. Both the direct ultrasonic signals and the ultrasonic signals passing through the crack within the micro-area range are simultaneously detected by the two probes. The ratio of the two describes the characteristics of the ultrasonic signals. Numerical analysis was used for theoretical verification. A hardware and software framework was developed for the detection of dual-probe laser ultrasonic turbine blades. Simulated blade microcracks were studied experimentally. The findings demonstrate that the dual-probe strategy can greatly increase the detection accuracy and decrease the relative error of micro-crack detection on the turbine blade surface from 18.0 to 14.2% when compared to the traditional method. Give an example for applications in laser ultrasonic engineering.

Hardened layer depth detection is a key technical indicator for evaluating the comprehensive performance of steel parts such as surface hardness and fatigue strength. Through establishing a numerical model of alloy steel heat treatment, this study innovatively proposes an ultrasonic phased-array based method for hardened layer velocity inversion and interface detection imaging. The research reveals that the time-distance curves of reflected waves received by multiple array elements exhibit characteristic hyperbolic features in the common midpoint gather domain. Velocity inversion was achieved by extracting the maximum energy of hyperbolic wavefield coherence in corresponding common midpoint gathers through velocity scanning. Building upon these findings, (f{kern 1pt} - {kern 1pt} k) wave equation offset technology is used to effectively solve the problem of uneven distribution or inclined interface imaging of the hardened layer caused by different heat treatment processes such as laser quenching. As a result, the relative error (RE) and root mean square error (RMSE) obtained by the hardened layer horizontal interface imaging obtained by this method are controlled at 1% and 0.03 mm and inclined interface are controlled at 1.5% and 0.04 mm respectively, with high detection accuracy and imaging resolution. This study provides a new technical approach for the nondestructive detection and characterization of complex surface modified layers (such as gradient coatings, nonuniform quenching layers, etc.).

For test samples that are modeled by shells of revolution—cylindrical, spherical, and toroidal—arbitrarily located relative to a piezoelectric transducer (PET)—we calculate the parameters determined by the adhesive properties of the couplant (surface tension, contact angle of wetting) and dynamic viscosity. These are the thickness of the couplant layer between the PET and the input surface and the maximum gap between the PET working surface and the curved input surface at which acoustic contact is maintained, as well as their effect on the echo amplitude. A comparison with experimental data is carried out.