Том 54, № 7 (2018)

Results of the experimental studies of an acoustic tract by the shadow testing method are provided. An inhomogeneous distribution of acoustic rays is revealed within the testing zone. The principle of producing a tomogram under small–angle probing is demonstrated. As a result of studying the error in determining the coordinates of flaws in different parts of the testing zone, it has been established that the least error corresponds to the flaw position at the center of the testing zone.

A nondestructive method has been proposed for determining the adhesive strength of a multilayer coating at the surface of a thick-walled object based on recording and statistically processing the backscattered signal in the form of an A-scan. The physical principles of the method, its ultrasonic implementation, and results of its experimental testing on thermal-spray coated specimens are presented.

The study of the full curve damage process of polypropylene fiber reinforced mortars under medium strain rate (10^–6 s^–1–10^–4 s^–1) could enrich the understanding of the dynamic damage characteristics of polypropylene fiber reinforced structures. In order to explore the physical mechanisms of polypropylene fiber in the dynamic damage process of the polypropylene fiber reinforced mortars. The real-time dynamic acoustic emission (AE) technology was applied to monitor the damage process of polypropylene fiber reinforced mortars at different strain rates. The analysis of characteristics of AE wavelet energy spectrum and the average AE peak frequency of polypropylene fiber reinforced mortars with different polypropylene fiber content at different strain rates were conducted. The results show that with the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increases first and then decreases and the average AE peak frequency increases gradually. The AE wavelet energy spectrum in ca8 frequency band and the average AE peak frequency decreases gradually with the increase of the strain rate, but them increases first and then decreases with the increase of polypropylene fiber content. The above AE characteristics could provide important information for the identification of dynamic damage mechanism of polypropylene reinforced fiber mortars.

The regularities of changes in the properties of the electrical response of reinforced concrete to an impact action in a four-point bending flexural test and the influence of the rebar cage configuration on the processes of failure in reinforced beams and on electrical response parameters have been studied. Criteria have been proposed for determining the stages of failure in reinforced concrete beams, based on electrical response parameters. The nucleation and growth of macrocracks in the tensile zones of reinforced beams is accompanied by a drop in the maximum cross-correlation coefficient of signal spectra at the current and previous loading levels to 0.45–0.6. An increase in the energy attenuation coefficient of electrical responses in a reinforced beam by 1.5–2.5 times can serve as a precursor to its impending catastrophic breakdown.

The topicality of this work is due to the importance of developing such a new-generation monitoring computer-aided measurement system intended for ensuring the safety of mining works and coal mining that would allow one to monitor all required parameters and defects in a massif. Additional optic-fiber losses have been investigated with the aim to develop the sensors of the computeraided measurement system for monitoring the technical condition of mining practice objects. Dependences between the number of deformed fiber sections and additional losses have been revealed for different wavelengths in the optical range; deformations and mechanical stresses in the optic fiber have been determined under stepwise pressure increase. Based on this data, a model has been proposed for an optic-fiber sensor intended for monitoring mechanical stresses in mine workings.