•Monitoring material degradation by combination of acoustic and electromagnetic data.•Three stages of evolution of Poisson's ratio as markers of degradation process.•Fracture criterion in terms of ...acoustic markers of damage and texture changes.
Microstructural changes under low-cycle fatigue of a metastable austenitic steel are monitored by a combination of the acoustic parameters: Poisson's ratio (more precisely, its change) as indicator of the “diffused” damage and anisotropy change as indicator of changes of texture. Three stages of the Poisson's ratio evolution are identified; they serve as markers of the process of material degradation. A criterion of fracture in terms of a critical combination of the changes of the mentioned parameters is proposed and tested. The challenge of separating the effects of damage accumulation and of the martensitic transformation on elasticity parameters is addressed by combining acoustic monitoring with the eddy current data.
The paper is devoted to a problem of synthesis of the automatic control system of a damping winch. The vessel descent-rise devices are used for vessel heave compensation and immerging depth ...stabilization of a towed underwater vehicle. Most of them have essential disadvantages. First, a cable destructs during its bending strains on descent-rise device's blocks. Second, a power of such device increases due to the compensation function. To eliminate these disadvantages it is offered to use a special damping winch. It is on the underwater vehicle. There are two controllers in the suggested automatic control system. The rope's tension controller is used for a heave compensation function of the damping winch and the rope's length controller is used for immerging depth stabilization of a towed underwater vehicle. For optimization of controllers the standard coefficients method with binomial decomposition and an optimal module method were used. Due to the offered approach vertical displacements of the underwater vehicle are reduced ten times at any sea state codes and stepless depth changing for a towed underwater vehicle is provided.
It is shown that in order to increase the sensitivity of ultrasonic contactless shadow testing of products made of polymer composite materials (PCMs), it is necessary to develop highly sensitive ...low-frequency broadband contactless piezoelectric transducers (PETs). The methods of providing both high sensitivity and a wide band of ultrasonic contactless PET are considered. The ultrasonic contactless high-sensitivity broadband PETs based on the use of mosaic contact PET technology, the choice of optimal matching layers, and the use of various options for the excitation of radiating PETs have been proposed and developed. It is shown that with the help of mosaic low-frequency broadband contactless PETs, one can achieve a high sensitivity of testing and ensure the accuracy of measuring acoustic characteristics (ultrasound velocity, density, etc.) with ultrasonic low-frequency shadow contactless testing of large-sized PCM products.
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.
An ultrasound wave measurement technique suitable for large compact-sized (where measured thickness is comparable with other dimensions) concrete structures is described. The technique is based on ...ultrasonic bulk wave velocity measurement Cl. The Cl value is determined
by the correlation method: correlation is established between the experimental spectral responses of a real sample and the series spectral responses of a finite element model calculated with different model ultrasonic velocity parameter values Cmod.j. To increase the accuracy of
the velocity measurement the multiplicative correlation method is used: cross-correlation is calculated between the spectral response curves obtained at different points on the sample and the spectral response curves of the finite element model calculated for the same points of the model.
It is shown that ultrasonic adaptive antenna arrays that are able to take the shape of a nonplanar surface of the tested product should be used for ultrasonic tomography of concrete building ...structures with a nonstandard surface configuration. It is also necessary to use adaptive methods of ultrasonic tomography allowing one to simultaneously determine the coordinates of defects and the speed of ultrasonic vibrations in concrete and to adjust the parameters of the probing signals to the characteristics of concrete products.
The results of studies on the use of the impact echo method for thickness gaging of compact concrete building structures are presented. It is shown that in compact building structures, in which the ...thickness being measured is comparable with other sizes of the test object, it is impossible to determine the sought-for thickness of the product based on its own resonant frequency due to the geometric dispersion of speed of sound. The influence of geometric dispersion is different for each compact product, and, as a result, it is necessary to measure the correction factor of the geometric dispersion of speed of sound
individually for each compact product. A technique is proposed for determining the factor
in compact products that ensures both the determination of the fundamental resonance frequency and the elimination of the influence of the geometric dispersion of speed of sound on the accuracy of thickness gaging of compact objects.
It is demonstrated that by analyzing the instantaneous spectrum of an ultrasonic signal transmitted in the shadow mode through the product under study, it is possible to determine the degree of ...difference in the structure of products made of finely dispersed polymer materials with different contents of one of the polymer components. This cannot be achieved with traditional methods of ultrasonic structuroscopy, based on analyzing the degree of attenuation and measuring the velocity of ultrasound in the material.
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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