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Proceedings Paper

Measurement of Lamb waves dispersion curves under narrowband monomode excitation using TV holography
Author(s): J. Luis Deán; José L. Fernández; Ángel F. Doval; Cristina Trillo
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Paper Abstract

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.

Paper Details

Date Published: 15 September 2006
PDF: 6 pages
Proc. SPIE 6341, Speckle06: Speckles, From Grains to Flowers, 63410B (15 September 2006); doi: 10.1117/12.695270
Show Author Affiliations
J. Luis Deán, Univ. de Vigo (Spain)
José L. Fernández, Univ. de Vigo (Spain)
Ángel F. Doval, Univ. de Vigo (Spain)
Cristina Trillo, Univ. de Vigo (Spain)

Published in SPIE Proceedings Vol. 6341:
Speckle06: Speckles, From Grains to Flowers
Pierre Slangen; Christine Cerruti, Editor(s)

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