► Ultrasonic shear wave method to assess concrete, stone, and masonry structures. ► Basic equipment features. ► Shear waves and DPC transducers description. ► Summary of SAFT-C image reconstruction ...algorithm. ► Laboratory and field applications.
In the mid-twentieth century, researches began developing digital technology. Digital format, simply stated, is the recording of information in a binary code of combinations of digits 0 and 1 1. Digital technology enables immense amounts of information to be compressed and stored 2. The advent of digital technology has encouraged many innovations in the computer industry, medical field, science and engineering, and other scientific fields. One of the most fascinating innovations of the last century was the development of digital three-dimensional (3D) imaging; some of which include images of the human body (MRIs, CAT-scans) and 3D digital cinematography. Similarly, but at slower pace, manufacturers of nondestructive testing equipment have also began to develop 3D imaging technology. Commercially available equipment to perform ground-penetrating radar, scanning impact-echo, and ultrasonic pulse velocity are already integrated with powerful software algorithms to produce two-dimensional (2D) or three-dimensional (3D) display of the test results.
This paper describes the basic features of the ultrasonic test equipment developed in the early 2000s, commercially known as Mira and Eyecon. These two instruments utilize a patented array of dry point contact (DPC) shear wave transducers to produce 2D and 3D tomographic images of the reflected waves. This new technology is allowing engineers to obtain in situ images of test results to understand the real time state of the structure under consideration. This paper also discusses an introduction to shear waves (S-waves), a brief description of the DPC transducers, the image reconstruction method, and synthetic aperture focusing technique (SAFT). Finally, several case studies involving laboratory and field applications on different kinds of structures and materials are presented. The conclusion section offers a summary of the main features and limitations of the Mira and Eyecon systems.
The features of propagation of ultrasonic pulses of a lateral transverse wave from a point source of vibrations on the surface of a layer are considered. The mechanism of this wave transforming upon ...reflections from the layer boundaries into a transverse wave beam directed to the layer surface at an angle close to 45° is described. Experimental confirmation of the excess of the amplitudes of the lateral wave signals over the signals of other waves propagating in the layer is presented.
We describe the physical meaning of the method of visualization by several sendings of probing ultrasonic waves with a plane front into the object and compare it with the method of digital aperture ...focusing. The results of experimental studies on the reconstruction of tomograms by these visualization methods based on ultrasonic data recorded when testing metal samples with reflectors are presented. It is shown that the plane wave method makes it possible to obtain images not only when the interelement delays of probing pulses provide the generation of real waves with a plane front, but also for delays that produce the virtual front of waves that do not physically exist. Coherent summation of images obtained at several angles of inclination of the wavefront forms a tomogram that is not much inferior in quality to the tomogram reconstructed by the method of digital aperture focusing. However, it takes several times less time to gather ultrasonic data; this is important for practical applications, in particular, for high-speed automated testing.
This study discusses ultrasonic and impact-echo methods as the most common nondestructive methods for determining concrete durability based on sound vibration velocity. It also reveals the influence ...of the signal of an acoustic surface wave on the accuracy of measuring resonant frequency in the spectrum of a cubic compact concrete sample. A through-transmission impact method is proposed to measure sound vibration velocity in cubic test concrete samples and determine concrete durability via an acoustic nondestructive method. An impactor and a receiving transducer are placed on opposite sides of the cube, several measurements are made at different positions of the impactor (or receiving transducer), and results of partial measurements are subjected to multiplicative processing to eliminate sound vibration and reduce errors in determining concrete durability.
A finite element model has been developed to study the propagation velocity of a horizontally polarized shear waves (SH-waves) in pipes of different diameters depending on geometrical parameters, ...excitation parameters, physical and elastic properties of the pipe material. The results of studies of the geometric anisotropy of the group and phase velocities of the SH-wave for a pipe with a diameter of 1020 mm with a wall thickness of 16 mm are presented. It has been established that in the case of isotropic properties of the pipe material, the velocity on the outer cylindrical surface in the direction of the envelope is 50 m/s more than on the generatrix. The radiation patterns of the SH-wave are given for the studied pipe size with radiation along the generatrix and envelope of the pipe. The results of experimental studies are in satisfactory agreement with the results of modeling.
The impact-echo method, which is a method of free vibrations, is used for testing building structures made of concrete that have the measured thickness
at least six times smaller than the other ...dimensions and is not used to test compact products in which the thickness
is comparable to the other dimensions. The problem with testing compact objects is that it is impossible to unambiguously determine the required resonant frequency
determined by the product thickness
on the spectrum of the compact product against the background of closely spaced numerous resonances determined by other test object dimensions. Another reason is that due to a strong influence of the geometric dispersion of the sound speed in compact products, it is necessary to calculate a correction factor
for each new compact test object. The article proposes a solution to the problem of testing compact concrete building structures using a multiplicative impact echo method that allows one to determine the desired resonant frequency, as well as using various versions of the correlation impact echo method that allow one to measure the speed of sound in compact products for the subsequent determination of concrete strength both in the process of cement solidification and during the operation of building structures in order to predict the trouble-free service life of buildings and structures.
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The results of calculating the adjustment factor for the geometric dispersion of sound velocity
in compact products of square cross section for various ratios of thickness to the side of cross ...section are presented. Using simulation in the ANSYS software environment, it has been shown that as the ratio increases, the main vibration mode transforms, causing the emergence of intrinsic resonance in the compact product. The transformation is from longitudinal waves in compact products of the “pile” type to Lamb waves in compact products of the “plate” type. At the same time, a nonlinear change in the coefficient
occurs in compact products that makes it possible to make a correction for the effect of geometric dispersion. The dispersion dependence of the coefficient
on the ratio of the thickness to the side of the product section has been calculated in compact square cross-section objects.
Physical principles and algorithms for reconstructing images of the inner structure of an object made of a solid material are considered. These are based on the pulsed echo method of ultrasonic ...testing using multielement antenna arrays focused on each point of the visualized region of the object by spatiotemporal processing of signals from a combination sounding of the object by all possible pairs of the antenna array. Substantial improvement of the image during testing of a plane-parallel object is obtained by using signals that are multiply reflected from the object boundaries; the use of different algorithms of image reconstruction is expedient for different types of discontinuity flaws.
Ultrasonic methods of inspection have come a long way in the last 75 years, since our compatriot S.Ya. Sokolov claimed the world's first patent for an ultrasonic method of nondestructive testing. A ...large number of ultrasonic NT devices have been developed in the interim, due to the wide range of problems that must be solved in manufacturing. Thus, serious attention has also been given to the matter of optimizing their nomenclature. For the ultrasonic NT of metal products, manufacturers use general-purpose flaw detectors, specialized detectors, thickness gages, and instruments that measure the physicomechanical properties and stress state of products. Although there is a large variety of manual testers, most of them operate on the principle of the echo-pulse method of ultrasonic NT. Here, a pulse of ultrasonic vibrations is sent into the metal product from the surface that is in contact with the transducer. The transducer then receives echo signals reflected from the opposite wall of the product and from any defects that are present. When piezoelectric transducers (PZT) are used, transmission of the ultrasonic vibrations into the product and reception of the echo signals are done through a layer of a liquid couplant (water, oil, or special gels). Direct-coupled, discrete-coupled, or oblique transducers are used, depending on the goal of the test. In modern ultrasonic testers, the data signals are processed using digital technologies.
