Caractérisation de défauts dans les milieux multi-diffusants : analyse de la méthode non linéaire d'interférométrie de la coda ultrasonore

Abstract : Coda waves are extremely sensitive to small disturbances of the propagation medium and therefore offer abundant information related to material damages. Recently, a method that combines Nonlinear acoustics and Coda Wave Interferometry (NCWI) has been proposed and applied to several types of materials (glass, mortar and concrete). In this thesis, numerical models (for a homogeneous medium and a heterogeneous medium) are developed using the spectral element method to study the nonlinear acosutique effects highlighted by a pump wave of large amplitude and low frequency. Several parameters are related to the influence of the pump wave: the change of the elastic modulus and the quality factor within an area of Effective Damage Zone (EDZ), the surface of the EDZ, the presence or absence of cracks in the EDZ, the change of the crack lengths and their number. The aim of numerical modeling is to be able to simulate ultrasonic coda waves in a multi scattering medium with the presence of different types of non-linearities and to propose numerical models that are useful for the diagnosis and optimization of experimental set-ups. An experimental validation of laws linking damage parameters to NCWI observables is performed on a perforated aluminum plate. The nonlinear effects are caused by the contacts of the threads of a variable number of screws in the plate. NCWI allows the characterization and monitoring of different types of non-linearities: it perfectly answers the needs of Non Destructive Evaluation and Testing for early damage detection in complex materials.
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Guangzhi Chen. Caractérisation de défauts dans les milieux multi-diffusants : analyse de la méthode non linéaire d'interférométrie de la coda ultrasonore. Sciences de l'ingénieur [physics]. Université Le Mans, 2019. Français. ⟨tel-02048353⟩

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