Vol 53, No 1 (2017)

It is shown that the microscopic material structure significantly affects the results of measuring mechanical stresses by the acoustoelasticity method. It is noted that the nonequiaxedness of the grain metal structure in steel flats leads to both the emergence of intrinsic acoustic anisotropy and the anisotropy of elastoacoustic coupling coefficients (EACC). Results of the research into connection between EACC and intrinsic acoustic anisotropy are presented for carbon and low-alloyed steels. The possibility of using generalized EACC values for determining mechanical stresses in high–acoustic-anisotropy materials of this class is substantiated. The results have made it possible to develop a mechanical-stress measurement technique that allows one to take measurements without running calibration tests on representative specimens of the test object.

A reference-free method is considered for concurrent measurement of the speed of ultrasonic vibrations and the thickness of concrete constructional products with ultrasonic antenna arrays that use the “focusing to a plane” algorithm.

The paper presents an experimental study of ultrasonic surface waves propagation in the low carbon steel specimens with different degree of degradation of microstructure and mechanical properties, subjected to tensile deformation. The purpose of this paper is to investigate and analyze the dependence between microstructure, mechanical and acoustic properties and to find appropriate parameters for stress state evaluation. For identification of degradation and stress state we use ultrasonic Rayleigh waves (URW) velocity variation obtained by in-line and off-line measurements. The degradation is imitated by structural changes caused by heat treatment.

A method is described for assessing the residual life of pipelines and articles made of structural steels. Dependences between applied stresses and parameters of registered magnetic noises are shown. Criteria are suggested for assessing the in-service destruction of pipeline metal by its magnetic parameters.

When switching to automatic output-quality testing systems, the aspiration for improving the detectability of insignificant deviations of the output parameters from the statutory ones necessitates the solution of a number of new problems. One of those is assessing the effect of the image-energy spectral density from an axisymmetric flaw on the reliability of its detection against background noise by both human and computer vision systems. Knowing this information is a necessary condition for developing new enhanced testing and evaluating techniques. Results are presented on the probabilities of false alarm and correct detection of axisymmetric circular or rectangular flaws depending on the signal-to-noise ratio (SNR) and the ratio of the flaw radius to the background-fluctuation correlation radius. It has been established that for small SNR, human vision is more effective than machine vision that implements the correlation detector algorithm and the Neyman–Pearson criterion.

A method for determining the probability of flaw detection by modeling optical images generated by X-ray nondestructive testing methods is described. Processes of formation of intrinsic noises in transducers have been studied. Normal distribution laws have been substantiated for the optical density in radiographic evaluation and the image brightness in fluoroscopic testing. Based on the image recognition theory, application of convolution in X-ray image interpretation has been justified and the accompanying change in the signal-to-noise ratio has been demonstrated. Dependence of flaw-detection probability on the shape and dimensions of test articles has been studied.