Russian Journal of Nondestructive Testing最新文献

This study has considered free and forced vibration analysis of a cracked Timoshenko beam exposed to a moving mass. It considers both analytical and finite element (FE) methods to analyse the vibration response of a simply supported beam carrying a moving mass and suffering from an open crack. Timoshenko beam theory has deliberated to investigate the dynamic behavior of a discretely simply supported beam with including shear deformation and rotational inertia under various configurations of open crack and moving mass conditions. The beam was divided into two segments, which obeyed the Timoshenko beam theory and the crack was modeled by a torsional spring with local elasticity at the connecting region of the two segments. The governing equations of the beam transverse vibration were solved based on Hamilton’s principle, and the obtained results are validated with previously published works, including numerical and experimental works. The effect of crack depth (CD) and crack location (CL) with the amount and speed of the moving mass on the dynamic response of the beam have been investigated, where the presence of the crack plays a key role in both free vibration characteristics and dynamic response of the Timoshenko beam. Hence, more nonlinearity and higher deflection in the dynamic behavior have perceived at CL = 0.5 and CD > 0.3 h. The obtained natural frequencies are generally decreased with increasing CD, in which significant drop in the 1st and 3rd natural frequencies have been identified when the crack is located at the mid-span of the beam. A frequency-domain representation under various mode excitations of moving load has evaluated to indicate the presence of the crack within the Timoshenko beam. Hence, the evaluation of frequency domain and dynamic deflection can be sensitive to indicate the presence of the crack and its severity.

Thermographic data is highly class-imbalanced and scarce while considering the temporal thermal profiles for automatic defect detection using deep learning. Training a supervised deep learning model requires a significantly equal amount of data. Unsupervised deep learning with one-class classification approaches has recently been introduced in thermography for composite inspection. This article proposes an autoencoder-driven anomaly detection model for automatic defect detection in quadratic frequency modulated thermography. The proposed model utilizes the pretrained stacked denoising convolution autoencoder (SDCAE) to extract deep features and feed them to a local outlier factor (LOF) for defect detection. This work analyzes the performance of the proposed SDCAE-LOF on a quick-responsive mild steel specimen with artificially embedded defects of various sizes at different depths. The performance is compared with the CNN-based deep anomaly detection model and other autorncoder models using multiple metrics to confirm the superior defect detection capability of the proposed method.

An infrared diagnostic of the scale of turbulence in the front of a natural fire is presented, as well as a comparison with the scale of turbulence in the air near the combustion source for a model grassland and crown fire. An analysis of the flame of a grassland fire reveals smaller turbulence scales than the flame of a crown fire. A fire-induced atmospheric turbulence at a height of 10 m is observed with the corresponding frequency of air temperature pulsation (0.1–6 Hz for a steppe fire and 0.1–3 Hz for a crown fire). The values of the structural functions of refractive index and temperature fluctuations are significantly higher than the background values and can be used for remote fire detection.

The conductor connection structure in gas-insulated transmission lines (GIL) is vital for power grid stability. Traditional inspections require power outages or fault signal detection post-failure, lacking real-time internal structure assessment. This paper introduces an in situ computed Tomography (CT) inspection technology for ultra-high voltage GIL conductors, aiming for non-destructive, high-precision, real-time monitoring. It analyzes Yuyang line GIL’s inspection needs and designs a system with a ring-clamping mechanism and adaptable scanning path. A specialized algorithm tackles incomplete data and imaging accuracy issues unique to GIL. Experiments show the technology’s ability to image GIL conductor connections in three-dimensional (3D), detect defects, and deformations, crucial for GIL’s safe operation and maintenance by identifying and preventing potential failures.

This study investigates the application of acoustic emission (AE) signals for monitoring fatigue damage during high-cycle fatigue (HCF) tests and proposes a fatigue damage monitoring strategy based on the Bhattacharyya coefficient (BC). A comprehensive description of the AE signal processing workflow is provided, encompassing the acquisition of signal waveform data, the calculation of probability distributions, and the utilization of the BC to quantify the similarity between reference and true distributions. Comparative analysis with traditional infrared thermography demonstrates that BC exhibits superior sensitivity in HCF tests, effectively capturing the progressive stages of fatigue damage. Additionally, the study evaluates the influence of varying bin widths on BC calculations and identifies an optimal bin width (BW). The optimal bin width not only balances the monitoring sensitivity and stability but also reduces the influence of external noise.

Special steel grades such as ChS-68 and 12Kh18N10T are used in nuclear power engineering, the space industry, medicine and other important areas of the technical sphere, and during operation are exposed to various types of destructive effects, including radiation load. This paper presents the results of a study of the effect of high-energy electron radiation on the acoustic properties of austenitic stainless-steel grade 12Kh18N10T. It was experimentally established that after exposure to electrons with an energy of 10 MeV, such parameters as the attenuation coefficient of ultrasound and the propagation velocity of transverse waves and Rayleigh waves change. These changes are due to defect formation and structural modifications of the material caused by radiation exposure. The obtained data allow us to conclude that it is necessary to take into account changes in the acoustic properties of steels when assessing their performance under radiation exposure.

To model the wave field of an ultrasonic transducer in materials with strong anisotropy (monocrystalline alloys of turbine blades, composite materials, welded joints, etc.), a physically descriptive asymptotic representation is obtained for quasi-spherical body waves excited by a surface source in an arbitrarily anisotropic elastic half-space. The asymptotics is derived by the stationary phase method from the integral representation of the solution in terms of contour integrals of the inverse Fourier transform. The peculiarities of their derivation and numerical implementation are discussed on the examples of a transversely isotropic composite material and a monocrystalline nickel alloy with cubic anisotropy. The dependence of  the stationary points on the direction is more complicated here than in the isotropic case, up to the appearance of multiple stationary points and folds, giving rise to additional wave fronts and caustics. A comparison is made with the plane waves described by eigensolutions of the classical Christoffel equation. It is shown that, despite the phenomenon of multiple wave fronts, varying the plane-wave orientation allows us to obtain the same group velocity vectors as for any of the waves described by the asymptotics.

Indirect-drive cryogenic target is a located in box-converter hollow spherical shell-capsule with spherically symmetric solid layer of deuterium–tritium fuel on its inner surface. Placing a cryogenic target in an experiment on ignition at a megajoule energy level facility is preceded by thorough characterization of all component elements of the target and characterization of finished target. This paper describes the characterization method of the entire external surface of the cryogenic target using a confocal scanning, and presents the results of developing an optical shadow method and an X-ray phase-contrast method for characterization the cryogenic fuel layer in the target. The results of stitching the entire external surface are used for interpretation of the results of experiments on the solid fuel layer formation in a cryogenic target. The developed program system for characterization of fuel layers is used for measuring the liquid fuel, for characterization of the solid fuel layer parameters and for evaluation the robustness of the characterization results.

Thermal barrier coatings are mainly used for thermal protection of turbine blades, and accurate non-destructive measurement of their thickness is a key factor in evaluating the integrity of blade quality. This article uses a reflective terahertz time-domain spectroscopy system to measure the thickness of thermal barrier coating samples, obtaining the refractive index of several thermal barrier ceramic coating material samples under different preparation conditions in the terahertz frequency band. Then, the reflective terahertz measurement system is used to obtain the time-domain signals of thermal barrier ceramic coating samples under different preparation conditions, extract different time-domain features, calculate the coating thickness, and compare them. The phenomenon of waveform broadening caused by dispersion during the transmission of terahertz waves in different samples was studied, and the impact of waveform broadening on the measurement of thermal barrier coating thickness was qualitatively analyzed. Compared with the results of metallographic thickness measurement, the deviation of the results is within the error range, and the comparison results show good consistency. It also provides useful reference for using terahertz technology to detect the thickness of thermal barrier coatings on turbine blades and evaluate structural quality.

The gas-plasma plume generated during laser selective melting of various alloys was investigated using atomic emission spectroscopy. It was demonstrated that the type of protective gas used affects the spectral characteristics. The use of helium as a process gas compared to argon reduces overall luminescence and the contributions of individual elements to the spectrum, indicating lower losses of these elements through evaporation under laser radiation exposure.