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Doctoral thesis viva voce: Thomas Bedetti

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Contact : thomas.bedetti@espci.fr

18 December 2012 10:00 » 13:00 — Langevin lecture theater

Study of multiple scattering of ultrasound for noise modeling of structure and characterization of stainless steel castings large grains

Thomas Bedetti, doctorant - PhD student Crédits ESPCI ParisTech
Thomas Bedetti, doctorant - PhD student Crédits ESPCI ParisTech This thesis presents the study of ultrasonic multiple scattering in media with a complex microstructure. In the context of Non-Destructive Testing (NDT), our media of interest consisted of forged and molded stainless steel samples often used in nuclear industry.

An experimental study has first been conducted using linear phased arrays, by measuring the inter-elements response matrix in a wide frequency band (1 MHz to 12 MHz). Values of characteristic parameters of multiple scattering have been deduced by post-processing this matrix (elastic mean free path, correlation distance). In addition, the coherent backscattering effect that can appear in those steels has been highlighted and studied. By exploiting this phenomenon, the diffusion constant D has been measured.

Then, a structural noise simulation method has been developed. It is based on the diffusion approximation and a numerical algorithm that generate random correlated noise. The experimentally measured parameters have been used as entries of the method. Accounting for the NDT domain, this method takes the influence of the transducers into account, at emission and reception. Comparisons have been conducted between simulated and experimental noise levels. Results have shown a good agreement when the diffusion regime is established.

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