No 2 (2023)

The article suggests using Plane Wave Imaging (PWI) technology for ultrasonic inspection of welded joints with narrow cutting to detect cracks at the interface of the fusion of the base and deposited metal. In comparison with the digital image focusing (CFA) method, the proposed method allows you to restore images of reflectors with a higher signal-to-noise ratio, with greater speed, both recording echo signals and restoring the image of discontinuities according to different acoustic schemes, taking into account the transformation of the wave type when reflected from the edges of the object of control. Numerical and model experiments have confirmed the effectiveness of using PWI technology to increase the speed of zonal control. The application of the coherent factor increased the signal-to-noise ratio of the crack model images, both for the FMC mode and for the PWI mode.

Friction stir welding has found wide application in the aircraft and rocket industries, primarily due to the possibility of obtaining welded joints with a strength close to that of the base material. One of the most promising methods of such welding is friction stir spot welding, which can serve as an alternative to electric contact spot welding and riveting of joints. To introduce friction stir spot welding into the production of critical products, it is necessary to consider issues related to non-destructive quality control of welded joints obtained by this welding method. The purpose of this work is to substantiate the applicability of the ultrasonic echo method for quality control of welded joints obtained by friction stir spot welding. The relevance of the work is confirmed by the fact that today there is no sufficiently complete information on the results of experimental studies aimed at analyzing the characteristics of welded joints obtained by friction stir spot welding. The authors of the article proposed to use the ultrasonic echo method of control. The control was carried out using an ultrasonic flaw detector with a separate-combined piezoelectric transducer on samples of welds made using friction stir spot welding. Flaws such as lack of penetration and root sticking were found in three samples as a result of ultrasonic testing, which was confirmed by metallographic studies. Samples in which no defects were found were subjected to mechanical tests, as a result of which it was found that the strength of the obtained welded joints is comparable to the strength of the base metal of the samples. Metallographic studies were carried out on samples after the absence of defects in welded joints was confirmed through mechanical tests. Thus, the relationship between the results of ultrasonic testing, metallographic studies, and mechanical tests is shown, which makes it possible to justify the applicability of the ultrasonic echo method for quality control of welded joints obtained by friction stir spot welding.

Subsurface detail extraction in active thermography demands high capturing rates, resulting in less exposure time, data redundancy, large bandwidth requirement, and wastage of sensing resources and memory. Compressive sensing (CS) is a data acquisition technique that overcomes these limitations by acquiring the signal at sub-Nyquist rates with fewer measurements considering the signal is sparse in some transformed domains and reconstructing the original response. This paper validates the application of CS in frequency modulated thermal wave imaging by experimenting on a quick responsive mild steel specimen with artificially simulated back hole defects. The discrete cosine transform is selected as sparsity prior and the orthogonal matching pursuit is used to reconstruct the original thermal response from the compressed measurements. The initial analysis is carried out on choosing the optimal sparsity parameter and the number of measurements, followed by the effect of the number of measurements on defect detection in various post-processing techniques used in frequency modulated stimulus. The defects detected and their qualitative analysis through assessing signal-to-noise ratio confirmed the suitability of CS for efficient reconstruction of thermal data and thereby enhancing the defect signature.