No 10 (2023)

The paper proposes to use the ultrasound tomography method based on the solution of the inverse coefficient problem to reduce the level of structural noise. Mathematical models used in ultrasonic tomogra-phy well describe such physical effects as refraction, diffraction and redispersion effects. It is logical to ex-pect that reconstruction of the internal structure of metallic samples using ultrasound tomography will be more efficient compared to digital antenna focusing (DAF) techniques. Due to the nonlinearity of the inverse problem of ultrasound tomography, an iterative MultiStage method is used to ensure convergence to the glob-al minima of the non-convexity functional. The paper presents the results of numerical experiments to restore the image of the internal structure of the welded joint, which may contain lateral cylindrical holes and crack models. The region of the welded metal is represented in the form of sections constructed according to the principle of Voronoi diagrams. In each section the velocity is constant and its value is randomly distributed. In the model adopted in the paper, the structural noise is formed due to multiple scattering at the boundaries of sections with different sound velocity. It was assumed that the antenna array is located on the outer surface of the control object of known thickness. The results obtained show that the tomographic method allows us to determine the shape and speed of sound in low-contrast reflectors, for which the CFA method is ineffective.

The depassivation of reinforcement caused by the reduction of concrete alkalinity due to the concrete carbonation process can induce the appearance of steel corrosion. The restoration of alkalinity can be done by chemical realkalinization (CRA) or electrochemical realkalinization (ERA) methods. In this context, the present work aims to evaluate the influence of the application time and the current density used in the electrochemical realkalinization process. For the development of the research, mortar samples were molded with a reinforced bar for electrical connection and remained for 24 months in a carbonation chamber. After this period, the carbonation depth that occurred was verified and then the specimens were submitted to the electrochemical realkalinization process using 3 different current values, 0.5, 1.0 and 1.5A/m2 and remained at different periods (7 , 14 and 21 days) in the recovery process. Additional tests of absorption, compressive strength, carbonation depth measurements, mercury intrusion porosimetry (MIP) and thermogravimetric analysis (TGA) were also carried out on reference, carbonated and realkalinized specimens. Based on the results of the tests, it was observed that the recovery process starts after 7 days with the lowest current density used. A better current density x application time ratio was also observed considering the results of the mercury intrusion porosimetry and thermogravimetric analysis tests in conjunction with the realkalinization process.

The paper considers the advantages and disadvantages of existing methods for temperature compensation of data from fiber-optic sensors based on fiber Bragg gratings as part of an embedded system for simultaneous testing of deformation and temperature of polymer composite materials. It is shown that when external temperature testing is impossible, it is most expedient to implement the method of two optical fibers with different sensitivity to at least one of these parameters due to different dopants. Technological issues related to the formation of a spatial topology and the provision of an effective interrogation of the embedded optical system for monitoring polymer composite materials by the two-fiber method are considered. The results of theoretical researches of a linear model of temperature compensation, a model that takes into account the influence of cross sensitivity, as well as a quadratic model of temperature compensation of optical testing data are presented. It has been established that the linear model is the simplest, however, when using it, one should take into account the error associated with the inaccuracy of the approximation of optical inspection data by a linear function. At the same time, it is shown that in order to improve the quality and reliability of the results of optical testing, it is advisable to use a quadratic model of temperature compensation, which provides an error level comparable to the error of the fiber-optic sensor interrogator. The results obtained can be used to develop methods for the simultaneous testing of samples, as well as monolithic and three-layer structures from structural layered of polymer composite materials with limiting molding conditions (temperature not more than 180 °C, specific pressure not more than 0,7 MPa), as in the process of bench and other tests, and, in the future, in real operating conditions.

A comparative analysis of the strength characteristics of two plastics, basic and engineering, which are used in 3D-printing, was carried out. The lateral surface of the destroyed wire samples was studied under the Altami MET 1C microscope to assess the uniformity of the strain distribution along the length.

This paper presents the results of studies of the effect of thickened repair anti-corrosion surfacing on pre-operational and in-service ultrasonic testing (UT) of the reactor vessel metal through anti-corrosion cladding in comparison with ultrasonic testing through standard surfacing provided for by the design documentation [1]. The paper estimates the distortion of acoustic fields of transducers of transverse and longitudinal waves and the detectability of defects during ultrasonic testing through cladding of different thicknesses and cladding with an inclined fusion zone from a thickness of 11 mm to a thickness of 18 mm