Vol 53, No 10 (2017)

A theoretical model has been proposed that makes it possible to explain peculiarities in the frequency characteristics of echo signals at the output of a receiving transducer depending on the geometrical parameters of a reflecting spherical surface when the transducer axis is displaced with respect to the surface’s center of curvature, that is, during scanning. It has been demonstrated that both with and without displacement of the transducer’s geometrical axis with respect to the center of curvature of the reflecting surface, the type of changes in the temporal dependences of the instantaneous frequency of signals at the output of the receiving transducer essentially depends on the geometrical parameters of a wavefront reflected from the surface: the smaller the radius of wavefront curvature at the aperture of the receiving transducer, the stronger the changes of the instantaneous frequency in the echo pulse. It has also been shown that the larger the curvature of this surface, the stronger the changes in the frequency characteristics of the echo pulse as the transducer axis is displaced with respect to the center of curvature of the reflecting spherical surface.

The structure and physical-mechanical properties of U8A high-carbon steel subjected to cold plastic deformation by hydrostatic extrusion have been investigated in a wide range of strain extents. Cold plastic deformation by hydrostatic extrusion has been shown to lead to the dispersion of the structure of U8A high-carbon steel. As the degree of true deformation increases, the ultimate strength and conventional yield limit of U8A steel monotonically grow by 2 and 3.6 times, respectively. Such parameters as coercive force, the number of jumps in magnetic Barkhausen noises, maximum magnetic permeability, residual induction, and the speed of elastic waves are more sensitive to changes in the dislocation density than in the dispersion of the grain and subgrain structure of extruded U8A steel. It has been established that at least two informative testing parameters are needed for nondestructive evaluation of the level of strength properties in extruded U8A steel. Those are coercive force (or maximum magnetic permeability, residual induction, the number of Barkhausen jumps, the speed of elastic waves) for a true deformation of up to 1.62 and the root-mean-square voltage of magnetic Barkhausen noises for true deformations above 1.62.

The history of thermal nondestructive testing and infrared thermography is briefly reviewed. The state-of-the art of thermal testing with a focus on its applications to testing of composite materials in aerospace industry is described.

Several domains are based on image processing and analysis. One of them is the radiographic inspection which is used in Non Destructive Testing (NDT). Active contours, snakes or deformable models are powerful techniques in image segmentation and restoration. According to the term related to the input data (image to be treated) those functionals are ranked on two categories: edge-based models and region-based models. Previous studies point out the advantages of the regionbased models over edge-based models. In this paper, we discuss and we summarize the strengths and weaknesses of four implicit region-based active contour models named: Piecewise Constant PC, Piecewise Smooth PS, Local Binary Fitting LBF and Global Local fitting energy GLF. After performing several experiments, we have concluded that all the models perform well with homogeneous images. On the contrary when images are strongly inhomogeneous, the models based on global (PC) or local (LBF) statistic intensity fail to segment such images. The PS model with its great advantage in preserving the contours has, as a drawback, the high CPU time consuming. The combination of local and global statistic image intensity gives to the GLF model the ability to better deal with such images in less CPU time.

When the repair mortars for the repair of concrete structures are exposed to high temperatures, it results in irreversible changes in their internal structure. These changes can be evaluated both on the basis of the compressive strength and flexural strength, but their evaluation can also be made using dynamic non-destructive methods. The article presents the findings on the use of parameters from the measurement by ultrasonic pulse and resonance method. Changes in the internal structure of repair mortars were evaluated on the basis of the dynamic Young’s modulus of elasticity and relative dynamic modulus of elasticity. The said parameters very well characterize the changes in the internal structure of the repair mortars, and their values decrease with the increasing temperature. Changes in the internal structure of the repair mortars also reduce the compressive strength and flexural strength. The researchers confirmed the suitability of the ultrasonic pulse and resonance method for evaluating the degree of damage to the internal structure of repair mortars exposed to high temperatures.