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Propagation des ondes ultrasonores dans les alliages de titane à fort fibrage : cohérence spatiale et diffusion multiple

Abstract : This manuscript is devoted to the study of ultrasonic wave propagation in complex media composed of elongated scatterers, and specifically titanium alloys comprising macrozones. This study is carried out using a linear phased array probe rotating around its axis and driven by a multi-channel programmable amplifier. The ultrasonic field backscattered by elongated scatterers presents an anisotropic spatial coherence and we show that the intensity backscattered by such a medium depends on the angle between scatterers elongation direction and the orientation of the probe in the plane perpendicular to the insonified direction. This dependence allows to determine the macrozones elongation direction and size, and to reduce the structural noise during a non-destructive evaluation. A three dimensional cartography of local elongation direction of macrozones is achievable by using two beams focused at the same point but with different directions of incidence. In order to assess the scattering regime at conventional testing frequencies, we developed a multiple scattering measure: the single scattering proportion estimator, based on Alexandre Aubry’s PhD thesis (UPMC 2008). Applied on TA6V and Ti17 alloys, it showed strong multiple scattering. We further extended this estimator to the case of water/solid complex interfaces. Lastly, we proposed a new visualization of forging simulation results, allowing to directly observe the real macrozones elongation direction and to better design inspection procedures.
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Aurélien Baelde. Propagation des ondes ultrasonores dans les alliages de titane à fort fibrage : cohérence spatiale et diffusion multiple. Acoustique [physics.class-ph]. Université Pierre et Marie Curie - Paris VI, 2017. Français. ⟨NNT : 2017PA066271⟩. ⟨tel-02367464⟩

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