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Vol 53, No 4 (2017)
- Year: 2017
- Articles: 9
- URL: https://journal-vniispk.ru/1061-8309/issue/view/11301
Acoustic Methods
Theoretical Aspects of Applying Lamb Waves in Nondestructive Testing of Anisotropic Media
Abstract
Theoretical aspects of applying Lamb waves to nondestructive testing of layered anisotropic media are considered. Propagation of Lamb waves is analyzed using a six-dimensional complex Cauchy formalism that allows one to obtain a closed-form equation for determining the dispersion of Lamb waves in media with arbitrary elastic anisotropy. The possibility for applying the higher modes of Lamb waves to nondestructive testing is noted.
243-259
Directional Characteristics of a Laser Pulsed Thermoacoustic Emitter in Nonmagnetic Metals
Abstract
Results of experiments on studying the dependence of the directivity of a pulsed laser thermoacoustic emitter of longitudinal and transverse ultrasonic waves that operates in a nonmagnetic conducting medium on the surface density of laser-radiation heat power are presented. The results can be recommended for nondestructive testing of nonmagnetic materials and articles with laser ultrasonic sources.
260-264
Localization of Reflectors in Plates by Ultrasonic Testing with Lamb Waves
Abstract
An algorithm is suggested for localizing flaws in thin-walled objects based on the analysis of dispersion characteristics of Lamb waves. It is shown that applying the technique of determining the instantaneous signal frequency by means of wavelet transform makes it possible to reconstruct extensive sections of frequency dependences of the group delay time for different modes of Lamb waves. An extra merit of the proposed method is its high noise immunity. It has been established that an optimum choice of the frequency range is required to minimize the experimental error, namely, in order to minimize the inaccuracy in determining distance one should choose the dispersion-characteristic section where the group delay time is long as compared with its nominal value while its frequency variation is maximum.
265-278
On Using an Acoustic Antenna Array for Testing Thermal Damages in Austenitic Steel by the Spectral Method
Abstract
Results of testing a technique for evaluating damages on the inner surface of austenitic-steel pipe samples by the spectral acoustic method with the use of an acoustic phased antenna array are provided. It is shown that accumulated damages can be revealed in the surface layer at a level of 10% of exhausting the resource of an article made of 12Kh18N10T steel.
279-285
On the Allowance for Direct Piezoelectric Effect when Studying the Pulsed Operation Mode of a Piezoelectric Emitter by d’Alambert’s Method
Abstract
An emitter in the form of a piezoelectric plate loaded on an aqueous medium is considered. Composite waveforms consisting of two half-periods are considered as electric signals fed to the plate, with one half-period exciting and the other one compensating. The pulsed transducer output signal is studied by D’Alambert’s method (without allowance for direct piezoelectric effect) and the Fourier spectral method. The similarity of the results indicates the correctness of applying d’Alambert’s method and the possibility for using it to assess the shape of signals emitted by the piezotransducer.
286-294
Examining the Experience of Revealing Delayed Deformation Corrosion Cracking
Abstract
The problem of skipping iron-oxide–filled damages in the welding junctions between the collector and Dn1200 branch pipe of the PGV-1000 steam generator in a VVÉR-1000 reactor facility is considered. The mechanism of crack nucleation and development is described. A hypothesis that cracks filled with corrosion deposits exhibit minimum reflectivity has been proposed and confirmed. Results of theoretical research into transmission and reflection of ultrasonic waves in the presence of a thin layer of corrosion products surrounded by pearlitic steel are provided. The reflectances of longitudinal and transverse waves from corrosion damages have been calculated and proved the viability of the hypothesis.
295-303
Possibilities for Increasing the Efficiency of Contactless Emitters of Acoustic Waves
Abstract
An electromagnetic-acoustic emitter has been designed that is capable of exciting widespectrum acoustic waves on a narrow section of the surface of metalware with a low voltage across the inductor. An engineering solution has been proposed that allows one to place emitter’s inductor directly on the surface of an article.
304-307
Finite Element Modelling of Lamb Waves Propagation in 3D Plates and Brass Tubes for Damage Detection
Abstract
Structural health monitoring (SHM) is becoming very significant for preventing catastrophic failures and uninterrupted operation. Due to continuous developments in SHM Lamb wave technique, finite element simulation is emerging as an initial step to be performed to visualize the potential solution to problem. The present study focus on the simulation of Lamb wave response using finite element method and its application to crack detection and identification in 3D aluminium plates and brass tubes using commercially available finite element package ABAQUS. Phase velocity and group velocity dispersion curve are initially plotted for aluminium and brass material. Subsequently simulation of distinct specimens with and without presence cracks is performed. Simulation results were validated and compared with actual results and were found to be in reasonably good agreement. A damage index parameter i.e. amplitude ratio is defined to notice the effect of crack dimensions variation. Interaction of Lamb waves with rectangular, semi-elliptical and semi-circular cracks (shallow to deep) is studied in detail. Also the application of signal processing techniques such as Spectrogram analysis, Fourier transform and Hilbert transform is also reported in this paper.
308-329
Magnetic Methods
330-335