Identification of the damping provided by a foam placed on a metal plate by an inverse vibration problem
Résumé
The reduction of vibration and acoustic levels of structures generally results in solutions with mass addition, which is a problem for products in the transport industry. Some solutions are sometimes studied for only one physical behaviour. This is the case of porous materials that are generally used for thermal insulation and/or sound absorption only. The purpose of this study is to better understand, or even control, the phenomena of dissipation on the vibration of structures when porous materials are inserted on them. To experimentally identify the damping added by the foam on a steel structure, a specific test bench is created. It consists of a foam-plate structure where the displacement field of the plate is measured thanks to a scanning laser vibrometer. For the post-treatment, an inverse method is used to determine locally the structural parameters. The Force Analysis Technique (FAT) and the Corrected Force Analysis Technique (CFAT) are here proposed to determine these structural parameters, such as the equivalent elastic modulus and the loss factor of the assembly. Mainly dissipation causes can contribute to the structure damping: dissipation in the foam skeleton, friction at the interface, viscothermic effects in the cell arrangements. Characterizations of materials properties and finite element models are then implemented to understand the influences of these different causes, depending of the foam and the type of contact at the interface.
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