Vol 55, No 8 (2019)

To increase the signal-to-noise ratio when testing materials with a high level of absorption, it has been proposed to use complex signals, formed on the basis of code sets employed in Code Division Multiple Access (CDMA) technology, as probing signals. The code sequences in the code sets have a low level of cross-correlation function and a delta-like autocorrelation function. Echo signals are recorded by the double-scanning method, in which the elements of an antenna array sequentially emit unique probing signals phase-shift keyed according to the Kasami code, with the echo signals being recorded in each radiation cycle concurrently by all the elements in the antenna array. Since the shape of the “side lobes” of the compressed echo signals is different for each shot, reconstructing the image of reflectors using digital focusing of the antenna (DFA) reduces the level of the “side lobes”. As a result, when different code sequences of length 15 are used for each antenna-array element, this level may prove to be lower than when one sequence of length 63 is used for all the elements. Provided that a unique code set is used in each position, reconstructing the DFA image when scanning with an antenna array should further reduce the noise level and the level of the “side lobes”. The effectiveness of the proposed approach was demonstrated in a model experiment on reconstructing the image of side-drilled holes in a Plexiglas™ SO-1 calibration block, when using Kasami codes of lengths 15 and 63.

The structural–phenomenological approach used to classify and split acoustic-emission signals into energy clusters, together with the parameters of detection frequency and weight content of location pulses in the clusters, allows real-time monitoring of main trends in damage accumulation at different structural levels and makes it possible to isolate signals generated during the failure of a structural material from accompanying mechanical interference and electromagnetic noise. An example of applying new criterion parameters to determining the moment of delamination of stringer runoffs from the shelves of the MC-21 airframe support strut under conditions of fatigue tests with a symmetric loading cycle is provided. Using the new criterion parameters and developed cluster-analysis techniques, employed, among other things, to discriminate location pulses in the field of spectral characteristics, an interconnection has been established between the process of breaking cohesive and adhesive bonds in the adhesive layer at the boundary between the stringer runoff fastening and the support strut shelves and the generated acoustic signals by their energy, waveform, and spectrum.

We investigated the features of defects on the rod and the “rod–end-terminal” contact of polymer and porcelain insulators using the developed integrated method for noncontact remote diagnostics of the performance of high-voltage insulators, including the initial detection of local areas with elevated electric-field gradients and the measurement of the set of characteristics of partial discharges. The emission of extra-large partial discharges was discovered, and their features were studied. Based on the measurement results, a diagram was constructed for electrophysical processes accompanying the emission of extra-large partial discharges, and their causes were established.

Results of trialing eddy-current testing techniques, validated on real operational defects and realistic artificial defects in the most critical parts, are presented. Significant differences have been established in the detectability of defects by various devices used in the industry according to various technological documentation. A method is proposed for standardizing sensitivity that should improve the reproducibility of the results of eddy current testing.

The algorithm makes it possible to simplify the procedure for processing results of the thermal testing aimed at both revealing latent defects and evaluating their transverse dimensions and shape. Applying this algorithm requires certain participation and experience of the thermography operator, as well as preliminary preparation of initial data by using techniques that increase the signal-to-noise ratio. The algorithm includes selection of defective zones on the thermogram of the test object, automated identification of points with extreme signals, and a pixel-by-pixel threshold analysis of the zones adjacent to these points, culminating in the construction of binary defect maps.

We consider the issues of expanding the range of measuring the shape and determining the deformation of a surface by wavefront detection methods such as holographic and speckle interferometry and speckle photography, based on a two-beam Jamin interferometer equipped with an image shifting device. A design has been developed for the two-beam interferometer with the device for shifting images in channels based on synchronously tilted plane-parallel plates. A technique for processing shear interferograms is decsribed. The accuracy of measuring the spacing of fringes in the interference pattern by Fourier-transform and wavelet-analysis based algorithms is studied. A block diagram of an automated device for interpreting speckle interferograms by the phase method based on a He–Ne laser in a magnetic field with a Zeeman frequency shift has been developed. It is shown that the accuracy of measuring the spacing of interference fringes can be as high as 0.02 of the interference fringe width.