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Étude des matériaux poreux thermo compressés pour la modélisation des écrans acoustiques automobiles

Abstract : This work was carried out in the framework of the project EcOBEx, whose main objective was to reduce the passby noise by mean of acoustic shields in the engine compartment of the vehicle. The acoustic shields are manufactured by thermocompression of uniform porous materials. The material’s properties and thickness evolve according to the degree of compression experienced by the material. The objective of this work is to propose some laws to predict the evolution of the materials properties from their initial non compressed values and the compression rate. Firstly, we focus on the parameters of the Johnson-Champoux-Allard-Lafarge (JCAL) equivalent fluid model : porosity, air-flow resistivity, tortuosity, viscous characteristic lengths, thermal characteristic length, static thermal permeability. Some analytical expressions are proposed to predict the variation of these parameters as a function of compression. They are derived from a physical model of cylindrical fibres where the fibre orientation variations induced by the thermocompression can be taken into account. The results are in good agreement with the measurements made two types of materials (open cell foam and fibrous). A generalized empirical model is finally proposed for the air-flow resistivity.In a second part, we focus on the elastic parameters, which are necessary to take into account the vibration of the skeleton. The quasi-static experimental method is first applied to study the evolution of the Young’s modulus along the compression rate for fibrous and open cell foams. A power law is then proposed to predict these variations. Finally, an inverse method for estimating the elastic properties of an orthotropic poro-elastic material from a vibratory measurement of a thermocompressed three layer sandwich structure is proposed. This method allows us to characterize the elastic properties of a porous material in a situation close to its actual application.
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Lei Lei. Étude des matériaux poreux thermo compressés pour la modélisation des écrans acoustiques automobiles. Acoustique [physics.class-ph]. Université de Technologie de Compiègne, 2018. Français. ⟨NNT : 2018COMP2428⟩. ⟨tel-02057743⟩

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