Measurement of beating effects in narrowband multimode Lamb wave displacement fields in aluminum plates by pulsed TV Holography

Fernández, José Luis Fernández; Trillo, Cristina; Doval, Ángel F.; Cernadas, Daniel; López, Carlos Pérez; Dorrio, Benito Vasquez; Miranda, Marta; García-Rodríguez, Francisco J.

doi:10.1117/12.612315

Cited by 3 publications

(7 citation statements)

References 2 publications

(2 reference statements)

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“…Therefore, once c L was known, we only had to calculate ν in order to characterize the plates. This resolution of the problem yielded a better accuracy than the former method described in [5]. The final results are displaced in Table 1 for the plates of thicknesses 2.98, 4.03 and 5.00mm.…”

Section: Methodsmentioning

confidence: 88%

“…The acoustic amplitude map allows confirming the monomode nature of the excited wave, since a beating would be detected if two or more modes were present in the plate [5]. On the other hand, the wavelength of the Lamb wave can be measured more accurately in the acoustic phase map than in the optical phase change map, because the modulation of the fringe amplitude due to the burst envelope is not present in the first one.…”

Section: Tv Holographymentioning

confidence: 89%

“…In this work we aim to excite narrowband single modes in the same plates of [5] and to determine their elastic constants from the experimental measurements of the wavelength of each individual Lamb mode. This parameter is obtained in the out-of-plane displacements maps rendered by our self-developed pulsed TV holography system.…”

Section: Introductionmentioning

confidence: 99%

“…With our experimental system we are able to detect this beating effect and in a former work we presented a method for determining the elastic properties of plates several millimetres thick. For this purpose we generated the A0 and S0 Lamb modes together in the plate and measured their beat wavelength [5].…”

Section: Introductionmentioning

confidence: 99%

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Measurement of Lamb waves dispersion curves under narrowband monomode excitation using TV holography

et al. 2006

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Ultrasonic Lamb waves provide a useful means for the nondestructive determination of the material elastic constants of shell structures such as plates, pipes, cans and many others. A new optical technique is described for the measurement of the dispersion curves of Lamb wave modes. The experimental system employs the wedge method for the excitation of Lamb modes in aluminum plates of thickness in the range of a few millimetres. Long tone-bursts are used in order to ensure the generation of narrowband ultrasonic waves. Furthermore, an appropriate selection of the wedge angle allows one to generate only the desired individual Lamb mode. The detection of the surface out-of-plane displacements is performed by our self-developed pulsed TV holography system, which evaluates the optical phase by the Spatial Fourier Transform Method. Inasmuch as a whole-field measurement is realized, the wavelength of the excited mode can be precisely measured from the TV holography displacement maps. On the other hand, the wave frequency is measured by a pointwise method, namely a Michelson speckle interferometer. The phase velocity is directly obtained as the product of these two values. Measurements are done for several frequencies and several Lamb modes, thus yielding a collection of experimental points. By fitting these results to the theoretical Rayleigh-Lamb frequency spectrum, values of the shear wave velocity and the Poisson's ratio of the plate material are obtained. For a better accuracy in the measurements, the longitudinal phase velocity was directly determined by the pulse-echo method. The additional knowledge of the mass density allows one to calculate the Young's modulus.

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Section: Methodsmentioning

confidence: 88%

Section: Tv Holographymentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Measurement of Lamb waves dispersion curves under narrowband monomode excitation using TV holography

et al. 2006

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“…The white halo is the spectrum of the speckle noise already present in the source images.The wavefield modulation that appears in the three last columns of Fig. 7 is due to a beating between two Lamb wave modes of the same frequency and different wavelenghts that propagate simultaneously in the material 12 . In the spectrum in Fig.…”

Section: Resultsmentioning

confidence: 99%

Spatiotemporal Fourier transform method for the measurement of narrowband ultrasonic surface acoustic waves with TV holography

Trillo

Doval

2006

SPIE Proceedings

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The measurement of ultrasonic surface acoustic waves of nanometric amplitude by TV holography (TVH) was demonstrated some years ago. The spatial periodicity of the wavefield across the optical phase difference maps was exploited to yield the mechanical amplitude and phase of the propagating wave. Now we present a refinement of the technique where we also profit from the temporal periodicity, at each point of the surface, of the displacement induced by the wave. We record a series of sets of primary correlograms, which are processed to yield optical phase-difference maps. We change slightly the delay between the excitation of the wave and the measurement from one recording to the next, so that the position of the wavefield on the resultant images is shifted accordingly. Every point on the surface, which oscillates at the frequency of the wave, is thus recorded at several instants of its oscillation cycle in consecutive optical phase difference maps of the sequence. We have then spatial periodicity at a given instant across each image and temporal periodicity at a given point on the surface across the series of images. This feature is exploited to calculate a three-dimensional Fourier transform of the data. As we employ narrowband ultrasonic waves, the spatial content of the spectrum is contained in a small region of the spatial frequency plane and within a thin slice of temporal frequencies, and can be easily filtered and inverse Fourier transformed to obtain the mechanical amplitude and phase of the wave. This method intends to extend the detection capability of the TVH technique to ultrasonic waves of lower amplitude.

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Elastic constants determination by direct measurement of the beat wavelength between A0 and S0 Lamb modes with pulsed TV holography

Fernández

Deán

Trillo

et al. 2007

Optics and Lasers in Engineering

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Elastic constants determination by direct measurement of the beat wavelength between A0 and S0 Lamb modes with pulsed TV holography", Optics and Lasers in Engineering, 45 (5) 618-630, 2007 Abstract A whole-field optical technique of high sensitivity, namely pulsed TV holography with phase evaluation by the Spatial Fourier Transform Method, is applied to the acquisition of instantaneous displacement fields of ultrasonic Lamb waves in aluminium plates a few millimetres thick. Two Lamb modes, the A0 and S0 ones, are simultaneously generated in the plate, producing a clear beating. Several values of the beat wavelength, corresponding to different excitation frequencies, are obtained by direct measurement of the distance between nodes in the wave field. The obtained values are fitted to the theoretical Rayleigh-Lamb frequency spectrum in order to determine the elastic constants of the plate material. We conclude that it is necessary to know the value of another parameter to univocally solve the problem, and so the bulk longitudinal wave velocity is measured by the pulse-echo method. Then the Poisson's ratio is obtained and, from these two parameters, the Young's modulus can also be determined.

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Measurement of beating effects in narrowband multimode Lamb wave displacement fields in aluminum plates by pulsed TV Holography

Cited by 3 publications

References 2 publications

Measurement of Lamb waves dispersion curves under narrowband monomode excitation using TV holography

Measurement of Lamb waves dispersion curves under narrowband monomode excitation using TV holography

Spatiotemporal Fourier transform method for the measurement of narrowband ultrasonic surface acoustic waves with TV holography

Elastic constants determination by direct measurement of the beat wavelength between A0 and S0 Lamb modes with pulsed TV holography

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