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1.
Comparison of systems for ultrasonic nondestructive testing using antenna arrays or phased antenna arrays 总被引:1,自引:0,他引:1
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2013,49(7):404-423
This paper considers the features of forming the images of reflectors using phased antenna array technology and the images obtained by the C-SAFT method by echo signals measured in by double-scanning mode. It is shown that in some cases the images obtained by the phased antenna array technology are less informative, while the images obtained by the C-SAFT method have a higher frontal resolution over the entire area of image restoration; the partial images restored at different positions of the antenna array can be coherently combined to obtain a high and homogeneous resolution throughout the entire volume of thickwalled articles and increasing the signal/noise ratio. For the sake of brevity, the registration of echo signals in the double-scanning mode and restoration of the images of reflectors by the C-SAFT method will be called digital focusing by an antenna array (DFA). The ability to restore the partial images of reflectors by once measured echo signals according to many acoustic schemes with their consequent combination into one high-quality image should provide reliable automation of the process of recognition and dimensioning of scatterers. Another advantage of the images obtained by the C-SAFT method with three-dimensional focusing is the possibility of restoring images in the same coordinate system when using antenna arrays on prisms of different configurations. This facilitates the joint analysis of the images. Speeds of forming the images by the technology of phased-antenna arrays and the images obtained by the C-SAFT method are comparable. If the testing technique is based on the use of nonlinear effects, then in this case PA flaw detectors have a distinct advantage over DFA flaw detectors. However, within the framework of linear acoustics, PA flaw detectors have no fundamental advantages over DFA flaw detectors. It is fairer to say that PA flaw detectors have drawbacks. This article shows images that illustrate the features of the images that were obtained by PA and DFA flaw detectors. 相似文献
2.
When running ultrasonic testing, it is possible to analyze reflector images that have been restored by the method of digital focusing with an antenna (DFA). To improve the quality of the reflector images, one can use a coherence factor (CF) or a sign coherence factor (SCF) obtained from the calculated delay times instead of counting echo signals. The images obtained with the calculation of the coherence factor make it possible to increase the signal-to-noise ratio and front resolution. It has been demonstrated by numerical and model experiments that reconstructing the CF- and SCF-images of reflectors is efficient when registering echo signals by both ordinary and thinned (TAA) antenna arrays, in which the distance between neighboring elements is much greater than the wavelength. 相似文献
3.
Determination of the reflector type from an image reconstructed using echo signals measured with ultrasonic antenna arrays 总被引:1,自引:0,他引:1
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2014,50(3):141-149
The application of the digital image focusing (DFA) method to the determination of the types of detected reflectors is considered. For this purpose two antenna arrays (AAs) are used, which are placed on opposite sides of the reflector and using which echo signals are recorded in three acoustic channels in the double-scanning mode. The first and second acoustic channels transmit and receive echo signals using the first and second AA, respectively, and the third channel is tuned so that the first AA transmits pulses and the second AA receives echo signals. Using signals in each channel, many partial images can be reconstructed in a common coordinate system according to different acoustic schemes with allowance for both multiple reflections from irregular boundaries of a tested object and effects of transformation of the wave types. Combining partial images makes it possible to obtain a high-quality image, in which the entire boundary of the reflector is seen and using which an attempt to automate the procedure of evaluating the reflector size and determining its type was made. Such an approach allows one to reduce the subjective influence of an operator on the testing results. It is shown that in order to increase the image resolution, the spectrum of echo signals can be extrapolated by the spectrum splitting method jointly with the construction of an AR model of their spectrum. The results of model experiments that confirm the possibility of determining the reflector type are presented. 相似文献
4.
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2014,50(4):227-238
A method that is proposed for calibrating an antenna array that is installed on a wedge provides refinement of the coordinates of the centers of piezoelectric elements. Precise knowledge of the coordinates will make it possible to obtain images in which reflections from reflectors will coincide with their actual positions with an accuracy no worse than a half wavelength. The calibration principle involves the minimization of the objective function that describes the difference between the antenna-array-measured echo signals from a 2-mm-diameter side drilled hole (SDH) at a depth of 12 mm and the calculated echo signals from the same hole. The algorithm operation was tested for echo signals calculated in the CIVA program. The calibration results for several antenna arrays on wedges and images of an SDH are presented, which were obtained using the method for digital antenna-array focusing (DAAF) for various acoustic systems. 相似文献
5.
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2013,49(2):77-92
A modified method of combined SAFT (C-SAFT) for restoring the images of reflectors is considered; it allows the multiple reflection of a pulse from the boundaries of the wall of a cylindrical inspection object. To verify the efficiency of the proposed algorithm, images of a crack were restored from echo signals that were calculated using the CIVA software package, which is intended for modeling the propagation and scattering of ultrasonic pulses. It was shown in a model experiment that the consideration of changes in the pulse phase during reflection from the inspection-object boundaries at various incident angles of an S-wave in the image-restoration algorithm increases the frontal resolution by more than two times. The consideration of five reflections from the inspection-object boundaries made it possible to obtain images of reflectors by the M-C-SAFT method using many acoustic schemes. The images allow one to determine the type of defects, as well as their dimensions and location in the depth of the wall of a pipeline that is 720 mm in diameter. 相似文献
6.
E. G. Bazulin A. E. Bazulin S. A. Kokolev T. M. Gur’eva 《Russian Journal of Nondestructive Testing》2014,50(6):307-317
A method of automated ultrasonic testing based on the use of a PAA flaw detector for the recording of echo signals followed by the reconstruction of the image of reflectors by applying the 3D variant of the method of projection in the spectral space (3D-PSS) is considered. Customized setting of the PAA flaw detector makes it possible to simulate the operation of many single-element transducers with different angles of incidence. This approach allows one to obtain the images of reflectors with a high resolution and a high signal-to-noise ratio at a depth of more than 100 mm. A procedure for the calibration of an antenna array on a prism operating in the mode of emulation of several piezoelectric transducers with different angles of incidence is discussed. The results of a testing a fragment of the support billet for the ITER diverter when obtaining the images by the classical PAA method and with the use of 3D processing, which demonstrate the efficiency of the developed testing technology, are presented. 相似文献
7.
A. E. Bazulin E. G. Bazulin A. Kh. Vopilkin S. A. Kokolev S. V. Romashkin D. S. Tikhonov 《Russian Journal of Nondestructive Testing》2014,50(2):92-108
A 3D variant of the coherent method of projection in the spectral space (PSS) for obtaining images of reflectors on the basis of measured echo signals is considered. Its application allows recon-struction of reflector images with a high frontal resolution in both the main plane of an ultrasonic transducer and an additional plane. The application of the PSS method is especially efficient when a reflector is far from the receiving aperture. In this case, it is possible to increase the signal-to-noise ratio by more than 12 dB and a tenfold increase in the frontal resolution can sometimes be attained as compared to the 2D layer-by-layer variant of the PSS method. Examples of the application of this method during reconstruction of reflector images in a specimen of the wall of a chemical reactor, in the case of multiple reflections from the walls of a welded T-branch with an overlaid plate (WTP), and when testing large-diameter studs and supports of the divertor, which is manufactured as part of the work on the thermonuclear reactor (ITER) project, are presented. The efficiency of applying the 3D variant of the PSS method for testing at large depths is shown. 相似文献
8.
Reconstruction of flaw images by the C-SAFT method from echo signals measured by an antenna array in the triple-scanning mode 总被引:1,自引:0,他引:1
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2012,48(1):1-14
The application of antenna matrices (AMs) for obtaining flaw images during automated nondestructive ultrasonic testing is
considered. The conventional technique of using an AM as a phased AM (PAM) has a number of drawbacks. One of them is related
to the small number of AM elements and consists in a low frontal resolution of the thus-formed images. Scanning with an AM
operating in the double scanning mode, viz., the so-called triple-scanning mode, allows coherent summation of partial images
for each position and obtaining a resulting image with a frontal resolution that cannot be attained with a PAM. In order to
test the serviceability of the proposed algorithm in the CIVA program, echo signals reflected from a crack model with a height
of 6 mm and a length of 30 mm in a tested object, which simulated a welded joint of a pipeline with a conventional diameter
of 800 mm (дy800), were calculated. The results of the reconstruction of images of model objects in the form of a drilled
side hole with a diameter of 6 mm at a depth of 15 mm in a CO-2 specimen and a fatigue crack in a welded joint of a д y800
pipeline are presented. To reduce the influence of reverberation noise, a B-type median template was subtracted from echo
signals. The flaw images that were reconstructed in numerical and model experiments demonstrate the efficiency of the proposed
algorithm. 相似文献
9.
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2010,46(11):789-797
A modification of the SAFT method for obtaining flaw images in test objects containing three regions with different velocities
of sound (SV) is proposed. Complex composite welded joints and repair welds are classified as objects in which the SV in a
welded joint may differ from the velocity in a parent metal by >5%; therefore, a high-quality image of flaws can be obtained
by taking different SVs into account. To solve this problem, a method for obtaining a test object with three regions with
different SVs is proposed. The delays of propagating ultrasonic pulses were calculated using the Fermat principle. The results
of reconstructing flaw images in a 300 welded joint from echo signals obtained as a result of numerical simulation by the
finite-element method are presented. The images obtained by the SAFT method without taking different SVs into account are
displaced from their true position, thus they do not allow determination of their coordinates and location. Consideration
of different SVs allows one to obtain unshifted reflections of flaw images and, hence, evaluate the types and dimensions of
flaws more accurately. 相似文献
10.
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2005,41(11):762-773
The possibility of using a scheme for separate detection of echo signals for obtaining high-quality flaw images is substantiated. A conventional algorithm for obtaining images by the projection method in the spectral space and an algorithm for obtaining images that is not limited by the approximation of a plane incident wave are considered. Coherent storage of images reconstructed from echo signals, which were detected in a separate scheme but at different positions of the radiator (transmitter), reduces the speckle-noise level and increases the resolution of flaw images. Positive and negative features of these algorithms are analyzed. Numerical and model experiments have demonstrated the feasibilities of different schemes of detecting echo signals for obtaining flaw images. 相似文献
11.
The possibility of using homomorphic filtration of ultrasonic echo signals, as a preliminary data processing method, for upgrading the flaw images obtained during coherent echo-signal processing is considered. Homomorphic filtration makes it possible to attenuate the effect of multiplicative noises appearing in the data recording, such as variation of the acoustic contact or the rough surface of the tested object. Obtaining of the images consists of the following stages: calculation of holograms on the basis of measured echo signals, taking the logarithm of the calculated holograms, determination of the hologram spectrum, projection operation in the spectral space, and the Fourier transform. The results of the practical use of homomorphic filtration for expertise of flaw dimensions in austenite welded joints of 325 × 15-mm stainless-steel pipelines are given. 相似文献
12.
O. V. Nemytova A. B. Rinkevich D. V. Perov 《Russian Journal of Nondestructive Testing》2012,48(11):649-661
A comparative analysis of the frequency parameters of echo signals from artificial reflectors of different shapes and from a natural spill-type flaw has been performed. The use of the instantaneous frequencies of ultrasonic signals that correspond to certain instants inside a pulse was suggested as an informative parameter for determining the flaw type. Instantaneous frequency is estimated based on the algorithm of the continuous wavelet transform, which increases the noise immunity of the method. It is shown that for the algorithm to be practically implemented it is appropriate to present the results in the form of dimensionless parameters, namely, normalized frequency deviations determined between the pulse center, edge, and tail. Their joint application makes it possible, in particular, to reliably distinguish echo signals that are reflected at junction flaws that rise to the surface of a test object (notches, dihedral angles, and spills of the weld joints), flat specimen surfaces, and local flaws, such as cylindrical side through holes and flat bottom drills. 相似文献
13.
The possibility of using the maximum-entropy method in ultrasonic nondestructive testing for increasing the resolution of echo signals 总被引:1,自引:0,他引:1
The problem of deconvoluting echo signals via regularization according to the maximum entropy method followed by the reconstruction of 2D images via the Fourier transformation synthetic aperture focusing technique (FT-SAFT) is considered. Numerical and experimental simulations have been performed. The possibility of improving the ray resolution of echo signals and reducing the speckle-noise level is demonstrated. The results obtained are compared to the results of constructing an AR model of the spectrum of echo signals. 相似文献
14.
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2011,47(1):30-44
The application of antenna arrays (AAs) for obtaining flaw images during automated non-destructive testing is considered.
The conventional technique of using an AA as a phased AA has a number of drawbacks. An alternative approach is proposed in
which echo signals are registered using an AA operating in the double scanning mode, and a modified algorithm of the combined
SAFT, which takes into account multiray ultrasound propagation with consideration of transformations of wave types upon reflections
from irregular boundaries of a test object, is used to obtain flaw images. The results of testing a specimen with a model
of a volumetric flaw in the form of a 2-mm-diameter side hole drilled at a depth of 12 mm and a specimen with a crack model
with a tip at a 12-mm depth are presented. Both specimens have rough bottoms. The obtained images allow determination of not
only the dimensions and locations of flaws, but also their type. 相似文献
15.
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2016,52(8):425-442
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). 相似文献
16.
Russian Journal of Nondestructive Testing - The disadvantage of using the digital focusing with an antenna (DFA) method to produce an image of reflectors is a large volume of echo signals and an... 相似文献
17.
E. G. Bazulin 《Russian Journal of Nondestructive Testing》2006,42(1):51-59
The possibility of increasing the signal-to-noise ratio by the method of echo-signal spectrum splitting jointly with spectrum extrapolation is considered. The essence of the method proposed is that the echo-signal spectrum known within a given frequency range (f min, f max) is divided into several subranges (f min i , f max i ). The construction of the AR model of the echo-signal spectrum allows the spectrum extrapolation from each subrange by an interval (f min e , f max e that far exceeds the initial interval. This means that, with the use of one echo signal, a set of signals can be obtained, the adding together of which increases the signal-to-noise ratio and ensures an ultrafine beam resolution for flaw images. The presented results of processing echo signals, which were obtained in numerical and model experiments, confirm the efficiency of the proposed technique for processing echo signals. 相似文献
18.
E. G. Bazulin D. A. Konovalov M. S. Sadykov 《Russian Journal of Nondestructive Testing》2018,54(8):539-545
When developing ultrasonic testing techniques for such complex objects as composite welds, the method of finite differences in time domain (FDTD) can be used to calculate echo signals in numerical experiments. Since the FDTD method is based on explicit numerical solution of the wave equation for an elastic medium, it can be used to take account of such effects as the emergence of a run round wave on a volume reflector, the transformation of a longitudinal wave into a lateral one under scattering of ultrasound by a crack, and the rescattering of pulses between reflectors and test-object boundaries. Applying the FDTD method to modeling the propagation of ultrasound in the sample with a high pattern noise and in the samples made of anisotropic inhomogeneous materials is substantiated. The FDTD calculation of the direct problem of propagation of elastic vibrations in a solid may prove useful when solving the inverse problem of ultrasonic nondestructive testing. 相似文献
19.
A. E. Bazulin E. G. Bazulin D. A. Koval 《Russian Journal of Nondestructive Testing》2009,45(7):452-463
The question of applying the TANDEM scheme for reconstructing flaw images by the SAFT method is considered. When the reflection
of rays from a bottom is taken into account, it becomes possible to reconstruct the image of a boundary of a vertically oriented
planar flaw. Formulas are proposed for calculating the optimal parameters of the scanning scheme for data collection according
to the TANDEM scheme and the resolution is estimated. It is shown that the depth resolution for images obtained taking into
account the reflection from the bottom is much worse than that for a direct beam. To increase the resolution, it is necessary
to use coherent summation of images obtained for the same test object at different bases. This is confirmed by model experiments. 相似文献
20.
The geometry of glass knife edges for ultramicrotomy was studied with nanoscale resolution using scanning force microscopy (SFM) in the contact mode. The local shape of the cutting edge was estimated from single line profiles of the SFM topographic images by taking into account the exact radius of the ultrasharp silicon tip. The tip radius was estimated from secondary electron micrographs recorded at low voltage by field emission scanning electron microscopy (FESEM). The radius of the investigated cutting edges was found to be in range 5–20 nm. The results obtained illustrate that the combination of SFM and high resolution FESEM provides a unique means to determine precisely the radius of glass knives. 相似文献