Etude théorique et expérimentale des résonances mécaniques locales de modes guidés par des structures complexes.

Abstract : This PhD thesis is about Zero Group Velocity Lamb modes. For these peculiar modes, the group velocity vanishes and the phase velocity remains finite, giving rise to narrow local resonances whose properties are very interesting. Attractive prospects in non destructive evaluation can be found because the frequency of those modes depends on the thickness and the mechanical properties of the plate. The behavior of the modes has primarily been explained. The experimental study have been lead using a non-contact optical set up including a pulsed laser source and an interferometric probe for the generation and the detection of those modes. The resonances have been used to determine the thickness and elastic constants of plates and of an anisotropic pipe. Then, the lateral resolution of the thickness measurement has been studied. The influence of the plate edge has been explored : an abrupt transition between the first ZGV resonance and the edge resonance has been observed at the distance of one thickness to the edge. The effect of the deposit of a thin layer on the ZGV resonances has then been numerically studied, which permitted to measure the thickness of a few hundreds nanometers thin gold layers deposited on a millimetric substrate. Finally, the function of the losses has been examined for two different cases, the intrinsic attenuation and the radiation of a fluid in contact with one face.
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Maximin Cès. Etude théorique et expérimentale des résonances mécaniques locales de modes guidés par des structures complexes.. Acoustique [physics.class-ph]. Université Paris-Diderot - Paris VII, 2012. Français. ⟨tel-00986632⟩

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