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Vol 52, No 8 (2016)
- Year: 2016
- Articles: 7
- URL: https://journal-vniispk.ru/1061-8309/issue/view/11287
Acoustic Methods
On some paradoxes in the analysis of pulsed operation mode of acoustic transducers by the method of integral transformations
Abstract
Reasons for the appearance of “precursors” and “tails” in the analysis of pulsed operation mode of acoustic transducers by the method of integral transformations are considered. It is emphasized that the reason is the impossibility to make an accurate allowance for the actual dependence of the complex wave number on frequency over the entire frequency range.
421-424
Reconstructing reflector images in ultrasonic testing of isotropic inhomogeneous media
Abstract
A modification of the C-SAFT algorithm has been suggested that makes it possible to take inhomogeneous properties of the test object into account in order to improve the quality of reflector images. The algorithm is based on calculating the field that is reflected by a point reflector by using the theory of ray propagation of sound in a stratified medium and makes it possible to allow for the presence of two types of waves, their conversion, and uneven boundaries of domains in the test object. Results of applying the algorithm to numerical experiments are presented and demonstrate the operability of the suggested approach when processing echo signals that are calculated by the method of finite differences in a time domain (FDTD).
425-442
Acoustic-emission evaluation of the process of destruction of a composite material under tensile, compression, and cyclic loads
Abstract
Destruction of the structure of polymer composite materials (PCMs) has been studied by acoustic-emission evaluation method under tensile, compression, and alternating-sign cyclic loads. A program of cluster classification of registered data arrays has been developed and used to reveal specific AE signals that are typical of studied load types. Detection of such signals in the course of deformation of the test samples indicates that irreversible structural changes occur in the composite, it is losing its carrying capacity, or a predestruction state that is critical for PCM has been reached.
443-456
Thermal Methods
Revealing surface microcracks in metal articles by excitation of high-frequency eddy currents with subsequent infrared-camera imaging
Abstract
A method has been developed for revealing microcracks in metal articles by excitation of high-frequency eddy currents with subsequent recording of the temperature relief with an infrared camera. The sensitivity, as measured by outside crack opening, is 8 μm; this corresponds to Level B of magnetic-powder testing. The method is technologically easier to implement than magnetic-powder one and can therefore replace the latter in many problems of testing.
457-462
Electric Methods
Effect of cyclic freezing–thawing on the parameters of electric response to elastic shock excitation of reinforced concrete
Abstract
General and distinctive features have been established for the effect that cyclic freezing–thawing has on the parameters of electric response to elastic shock excitation in steel and glass-fiber reinforced concretes. Based on frequency-time and autocorrelation analyses, criteria are suggested for assessing the deterioration degree of reinforced concrete under alternating-sign temperature action.
463-468
Nondestructive testing for flaws in the insulation of winding wires
Abstract
Peculiarities of discharge that is initiated by a flawed section of wire insulation that passes through a primary gas-discharge flaw transducer have been studied. Analysis of the structure of signals has been carried out, and possible mechanism and type of discharge in the sensor have been considered. Informative zones have also been singled out in the signal structure. A technique is described for testing enamel-insulated wires for flaws. The technique makes it possible to determine the number and extent of flawed sections in an enameled wire that is fed through the system at any variable speed. Ways and means are considered for reducing the errors in evaluating the number and extent of flaws. Flow chart of a faultiness-measurement device is suggested, and the principle of its operation is described.
469-477
General Questions of Nondestructive Testing
Remote testing of high-voltage insulators
Abstract
An integrated two-channel method has been suggested for remote testing of operating condition of high-voltage insulators. The method is based on concurrent registration and computer processing of partial-discharge signals that are detected by electromagnetic and acoustic sensors. Using the device that was created based on this method, diagnostic signs have been established that make it possible to distinguish between functional and faulty insulators under real service conditions.
478-483