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Journal ArticleDOI

The reflection of the fundamental torsional mode from cracks and notches in pipes

30 Jul 2003-Journal of the Acoustical Society of America (Acoustical Society of America)-Vol. 114, Iss: 2, pp 611-625
TL;DR: A quantitative study of the reflection of the T(0,1) mode from defects in pipes in the frequency range 10-300 kHz has been carried out, finite element predictions being validated by experiments on selected cases.
Abstract: A quantitative study of the reflection of the T(0,1) mode from defects in pipes in the frequency range 10-300 kHz has been carried out, finite element predictions being validated by experiments on selected cases. Both cracklike defects with zero axial extent and notches with varying axial extents have been considered. The results show that the reflection coefficient from axisymmetric cracks increases monotonically with depth at all frequencies and increases with frequency at any given depth. In the frequency range of interest there is no mode conversion at axisymmetric defects. With nonaxisymmetric cracks, the reflection coefficient is a roughly linear function of the circumferential extent of the defect at relatively high frequencies, the reflection coefficient at low circumferential extents falling below the linear prediction at lower frequencies. With nonaxisymmetric defects, mode conversion to the F(1,2) mode is generally seen, and at lower frequencies the F(1,3) mode is also produced. The depth and circumferential extent are the parameters controlling the reflection from cracks; when notches having finite axial extent, rather than cracks, are considered, interference between the reflections from the start and the end of the notch causes a periodic variation of the reflection coefficient as a function of the axial extent of the notch. The results have been explained in terms of the wave-number-defect size product, ka. Low frequency scattering behavior is seen when ka 1.
Citations
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Journal ArticleDOI
TL;DR: In this article, the effect of pipe size, defect size, guided wave mode and frequency on the reflection from notches was analyzed for a 3-in. schedule 40 steel pipe.
Abstract: Ultrasonic guided waves are used for the rapid screening of pipelines in service and simple, standard testing procedures are already defined. The implementation of the method enables the localization of the defects along the length of the pipe and offers a rough estimate of defect size. In this article we present a systematic analysis of the effect of pipe size, defect size, guided wave mode and frequency on the reflection from notches. The maximum and minimum value of the reflection coefficient at varying axial extent are identified and used for the purpose of defect sizing. Maps of reflection coefficient as a function of the circumferential extent and depth of the defect are presented for a 3 in. schedule 40 steel pipe. An approximate formula, which allows these results to be extrapolated to other pipe sizes, is proposed and evaluated.

253 citations

Journal ArticleDOI
TL;DR: In this paper, the interaction of Lamb wave modes at varying frequencies with a through-thickness crack of different lengths in aluminium plates was analyzed in terms of finite element method and experimental study.
Abstract: The interaction of Lamb wave modes at varying frequencies with a through-thickness crack of different lengths in aluminium plates was analysed in terms of finite element method and experimental study. For oblique-wave incidence, both numerical and experimental results showed that the wave scattering from a crack leads to complicated transmission, reflection and diffraction accompanied by possible wave-mode conversion. A dual-PZT actuation scheme was therefore applied to generate the fundamental symmetrical mode (S0) with enhanced energy to facilitate the identification of crack-scattered wave components. The relationship between crack length and the reflection/transmission coefficient obtained with the aid of the Hilbert transform was established, through which the crack length was quantitatively evaluated. The effects of wavelength of Lamb waves and wave diffraction on the properties of the reflection and transmission coefficients were analysed.

163 citations

Patent
06 Mar 2013
TL;DR: In this paper, the basic principles of a time reversal based pulse position modulation (TR-PPM) method are presented, and the authors also experimentally demonstrate data communication with PPM on pipes.
Abstract: Embedded piezoelectric sensors in large civil structures for structural health monitoring applications require data communication capabilities to effectively transmit information regarding the structure's integrity between sensor nodes and to the central processing unit. Conventional communication modalities include electromagnetic waves or acoustical waves. While guided elastic waves can propagate over long distances on solid structures, their multi-modal and dispersive characteristics make it difficult to interpret the channel responses and to transfer useful information along pipes. Time reversal is an adaptive transmission method that can improve the spatiotemporal wave focusing. The present disclosure presents the basic principles of a time reversal based pulse position modulation (TR-PPM) method and demonstrates TR-PPM data communication by simulation. The present disclosure also experimentally demonstrates data communication with TR-PPM on pipes. Simulated and experimental results demonstrate that TR-PPM for data communications can be achieved successfully using guided elastic waves.

159 citations

Journal ArticleDOI
TL;DR: A finite element model of the elementary transducers has been developed and shows that magnetostrictive EMATs directly applied on mild steel plates have comparatively poor performance that is dependent on the precise magneto-mechanical properties of the test object.
Abstract: Guided wave inspection has proven to be a very effective method for the rapid inspection of large structures. The fundamental shear horizontal (SH) wave mode in plates and the torsional mode in pipe-like structures are especially useful because of their non-dispersive character. Guided waves can be generated by either piezoelectric transducers or electro- magnetic acoustic transducers (EMATs), and EMATs can be based on either the Lorentz force or magnetostriction. Several EMAT configurations can be used to produce SH waves, the most common being Lorentz-force periodic permanent magnet and magnetostrictive EMATs, the latter being directly applied on the sample or with a bonded strip of highly magnetostrictive material on the plate. This paper compares the performance of these solutions on steel structures. To quantitatively assess the wave amplitude produced by different probes, a finite element model of the elementary transducers has been developed. The results of the model are experimentally validated and the simulations are further used to study the dependence of ultrasonic wave amplitude on key design parameters. The analysis shows that magnetostrictive EMATs directly applied on mild steel plates have comparatively poor performance that is dependent on the precise magneto-mechanical properties of the test object. Periodic permanent magnet EMATs generate intermediate wave amplitudes and are noncontact and insensitive to the variations in properties seen across typical steels. Large signal amplitudes can be achieved with magnetostrictive EMATs with a layer of highly magnetostrictive material attached between the transducer and the plate, but this compromises the noncontact nature of the transducer.

149 citations


Cites background from "The reflection of the fundamental t..."

  • ...moreover, the driving frequency is representative of experimental conditions found in practice: frequencies in the range 10 to 250 kHz are often used [8], [33], [34], depending on the thickness of the test object and other experimental considerations....

    [...]

  • ...Furthermore, these wave modes do not show any out-of-plane particle displacement, thus they are not affected by the presence of (nonviscous) liquids in contact with the waveguide [8]....

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Journal ArticleDOI
TL;DR: It is found that reliable sizing of circumferential cracks in finite element simulations and experiments can be achieved if thecircferential extent of the defect is greater than 1.5 lambdaS, where lambdaS is the shear wavelength at the frequency of inspection.
Abstract: This paper deals with quantifying the performance of a technique for detection, location, and sizing of circumferential crack-like defects in pipelines using synthetically focused guided waves. The system employs a circumferential array of piezoelectric transducer elements. A torsional probing guided wave is excited using the array, which subsequently interacts with the reflecting features of the pipe, such as defects or weld caps. The recorded backscattered signals are synthetically focused to every point of interest in the pipe wall, to form an image of the reflecting features of the pipe. The defect image amplitude is used to estimate the defect depth, and the full width at half maximum of the defect image circumferential profile is used to estimate the circumferential extent of the defect. The imaging system is tested with data from finite element simulations and from laboratory experiments. It is found that reliable sizing of circumferential cracks in finite element simulations and experiments can be achieved if the circumferential extent of the defect is greater than 1.5 lambdaS, where lambdaS is the shear wavelength at the frequency of inspection. This result is theoretically valid for any pipe size, any axial defect location, and any inspection frequency. Amplitude gains of around 18 dB over an unfocused system have been observed experimentally in an 8-inch pipe with a 9 dB SNR improvement.

102 citations


Cites background from "The reflection of the fundamental t..."

  • ...More recently, the fundamental torsional guided wave mode T(0,1) has received considerable research interest and has been employed at lower frequencies (10–50 kHz) [5], [8], [22]....

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  • ...Finite element studies investigating the scattering from notches of varying circumferential extent, depth, and axial extent with l(0,2) incidence [21], [27] and T(0,1) incidence [8] of varying frequency also confirm ditri’s findings....

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References
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Book
01 Jan 1973
TL;DR: In this article, the authors apply the material developed in the Volume One to various boundary value problems (reflection and refraction at plane surfaces, composite media, waveguides and resonators).
Abstract: This work, part of a two-volume set, applies the material developed in the Volume One to various boundary value problems (reflection and refraction at plane surfaces, composite media, waveguides and resonators). The text also covers topics such as perturbation and variational methods.

5,211 citations

Journal ArticleDOI
TL;DR: The results indicate that Lamb waves may be used to find notches when the wavelength to notch depth ratio is on the order of 40, and the 2-D Fourier transform method is used to quantify Lamb wave interactions with defects.
Abstract: The interaction of individual Lamb waves with a variety of defects simulated by notches is investigated using finite-element analysis, and the results are checked experimentally. Excellent agreement is obtained. It is shown that a 2-D Fourier transform method may be used to quantify Lamb wave interactions with defects. The sensitivity of individual Lamb waves to particular notches is dependent on the frequency-thickness product, the mode type and order, and the geometry of the notch. The sensitivity of the Lamb modes a/sub 1/, alpha /sub 0/, and s/sub 0/ to simulated defects in different frequency-thickness regions is predicted as a function of the defect depth to plate thickness ratio and the results indicate that Lamb waves may be used to find notches when the wavelength to notch depth ratio is on the order of 40. Transmission ratios of Lamb waves across defects are highly frequency dependent. >

912 citations

Journal ArticleDOI
TL;DR: In this article, the authors used a commercial finite element (FE) code to study the propagation characteristics of ultrasonic waves in annular structures and demonstrated the potential of the FE method for problems when an analytical solution is not possible because of complicated component geometry.
Abstract: This paper reports on the application of guided waves techniques to nondestructively determine the structural integrity of engineering components. Specifically, this research uses a commercial finite element (FE) code to study the propagation characteristics of ultrasonic waves in annular structures. In order to demonstrate the accuracy of the proposed FE technique, the propagation of guided waves in a flat plate is examined first. Next, the propagation of guided waves in thick ring structures is investigated. Finally, these FE results are compared to analytical and experimental results. The results of this study clearly illustrate the effectiveness of using the FE method to model guided wave propagation problems and demonstrate the potential of the FE method for problems when an analytical solution is not possible because of “complicated” component geometry.

553 citations