Volume 55, Nº 1 (2019)

In this paper, based on the frequency distribution law of discrete wavelet de-noising, the expression of the optimal decomposition layer of wavelet de-noising is deduced. By simulating the signals of four different frequency bands, the optimal decomposition number of single frequency signal de-noising calculated by the expression has the same result as the composite evaluation index method. The acoustic emission signal of concrete cracking is a multi-frequency broadband wave. The signal optimal decomposition layer of the crack initiation phase and crack propagation stage obtained by the composite index identification method both are 5, same to the result of the expression calculated. This paper analyzed the variation law of de-noising composite evaluation index of the main frequency band of complex multi-main frequency wideband wave signal with the increase in the number of layers and proved the rationality of the parameter selection in the expression. Contrasting with the composite evaluation index method, the expression is suitable for the calculation of the simple and complex signal optimal decomposition number. It is easier and more reasonable.

Results of an experimental study of internal stresses in selectively heat-strengthened rails by an acoustoelastic method using the electromagnetic-acoustic method of input-reception of shear waves are presented. Results of modeling the stressed-strained state of a rail with critical stresses present in its bottom and data of an experimental tensometric study of residual stresses in the rail bottom are considered. An analysis of the results has confirmed a spread in stresses across different sections within a single rail, and also revealed an excess over the critical level of stresses in the surface layer of the rail bottom under compressive stresses in its head and web. A rejection criterion for acoustoelastic testing is proposed that conforms with the requirements of GOST (State Standard) 51685 in the case of both web cutting and rail bottom tensometry.

Examples of creeping in long-running shafts of high-temperature rotors in power turbines are given. The creeping manifests itself in the form of a spiral-shaped deformation of the surface of the axial channel and, at the same time, as spiral-arranged flaws within the thickness of the shaft, detectable by the ultrasonic method. The forces and moments of forces acting on the rotor during its operation are considered, as well as their connection with detected operational defects. Criteria for the state of metal in a rotor with operational defects are discussed with the aim to assess its residual life and ensure its safe operation.

Results of studying the use of film flux detectors for monitoring artificial continuity defects are presented. Photographs are provided for a film flux detector with images of magnetic fields due to holes 2.0 × 10^–3 m in diameter in an iron plate with a thickness of 6 × 10^–4 m and a hole 1.0 × 10^–2 m in diameter in an aluminum plate with a thickness of 2.0 × 10^–3 after exposure to magnetic field pulses with a rise time of approximately 2.0 × 10^–5–5.0 × 10^–5 s, as well as of fields that passed through gaps 1 × 10^–4 and 1 × 10^–5 m wide between joined aluminum plates with a thickness of 3.0 × 10^–3 m for different applied-field directions. Results of measuring the maximum value of the tangential H_τm (3.9 × 10⁴ A/m) and normal H_τm (3.3 × 10⁴ A/m) components of the strength of the total magnetic field near the surface of the aluminum plate (in the immediate vicinity to the hole in it) using a discrete magnetic-field sensor are presented. Based on the research, magnetic pulsed methods of searching for continuity defects in objects made of diamagnetic, paramagnetic, and ferromagnetic metals have been developed. These methods consist in exposing an object, with a flux detector atatched to it, to a magnetic field pulse and determining the defectiveness of the object based on the analysis of the optical image of magnetic field by studying the shape of the image and the distribution of gray levels (chromaticity) in it, while taking account of anisotropy parameters and the calibration characteristics of the sensor. The amplitude of the field pulse, its rise time, the shape of the leading and trailing edges, the number of pulses, the parameters of magnetic field spikes were preliminarily determined and the uniform illumination of the detector surface was ensured. Before use, the detector was demagnetized or polarized; the type and parameters of the magnetic field inductor were determined. It has been proposed to increase the image contrast by exposing the object–detector assembly to a series of pulses.

The vacuum intensification of the process of filling defects in stainless steel and glass samples with penetrants under liquid-penetrant testing has been studied experimentally. Results indicate a high efficiency of vacuum impregnation with small amounts of penetrants on tested surfaces, especially when detecting flaws with openings of 1–3 μm. It has been established that the sensitivity of testing is increased by 30–100% compared with the traditional technique.

The defect detection procedure of a radiographic image is a very important task. This is because of its importance regarding the safety of different industrial equipment. The defect detection procedures must reveal the defect region with the edges preserved. The radiography images are degraded by different noises caused by photon x-ray scattering, data acquisition and system errors. Due to the noise, radiography experts may encounter certain difficulties when extracting the defect region in the noisy images. This article presents a novel implementation of the Gabor filtering algorithm to improve contrast and denoise radiography images and detect the defects. Gabor filtering with automatic detection of noise level is a powerful contrast enhancement algorithm, but it tends to remove specific details from the processed images passing them off as noise. The performance of the proposed approach, the region defect, is revealed in radiographic images of different welded specimens. Results show major improvement not only in the noise attenuation, but also in the preservation of small details and the defect region.

General infrared image processing and analysis methods mainly include non uniformity correction, enhancement, noise reduction, segmentation, etc. The handling objects of these algorithms are ordinarily single images, which can improve the display effect of defects in infrared image and increase the signal-to-noise ratio. The active heat source excitation is usually used for defects detection in long pulse infrared thermal wave testing technology, so the collected image sequences are dynamic images. At the same time, as in-homogeneous characteristics of thermal excitation, the detection accuracy of defects is affected. Compared with ordinary infrared images, thermal dynamic image sequence is affected by uneven thermal excitation and wave flow. So the characteristics of the dynamic sequence should be analyzed, in order to get better defect display effect. Using the SVD (singular value decomposition, SVD) method for infrared image sequence reconstruction, and the component of surface temperature signal feature information has been extracted. Compared to the original image, the contrast and signal-to-noise ratio of the reconstructed image has been improved. Canny, LOG and other classical edge detection operators were used to detect the edge of infrared images, and their detection results were compared and analyzed. On the basis of analyzing the effect of the classical edge detection operators on the defect edge recognition in infrared images, a hybrid algorithm for edge detection based on Retinex-watershed-Canny operator is proposed for image edge detection, and the thermal barrier coating structure debonding defects’ edge has been recognized. A large number of useless and untrue boundary information around has been reduced, and the boundary contour of defects is more clear and continuous, which can improve the feature extraction effect of defects. The research work of this paper lay a certain foundation for the quantitative detection of defects.