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Many solutions exist to insure the NVH comfort of ground and air vehicles, like heavy mass (bitumen pads), viscoelastic treatments and absorbing foams. The trim foam appears as an alternative to heavy solutions. To know the potential of these foams, a study of their capacities to damp vibration is done. A system, composed of a suspended plate, with a foam on it, is characterized in different contact conditions at the foam-plate interface (glued or not) and with different foam type. An experimental test facility is developed to identify the global damping of the structure: a laser vibrometer measures the displacement field of the foam-plate structure, and then an inverse method is used to determine the structural parameters. By changing the contact at the interface, it is possible to identify the contribution of the friction forces to the global damping of the structure. Another type of damping is the viscoelastic damping due to the intrinsic characteristics of the trim foam.

This paper aims at identifying the flexural and shear complex moduli of a sandwich beam by simply measuring the displacement field and applying an inverse resolution of the Timoshenko beam problem. A first development [1] employed the RIFF technique (from the french "Resolution Inverse Filtrée Fenêtrée") [2]. This article presents an improvement, using the RIC method ("Résolution Inverse Corrigée" in french) that involves a correction of the finite difference scheme as originally suggested in [3]. By applying this method specifically to the Timoshenko beam problem [4], one can asses the viscoelastic parameters of composite beams, based on a coarse mesh measurement of the displacement field using a simple accelerometer and an instrumented hammer. An experimental validation conducted on a sandwich honeycomb beam with fibreglass faces allows satisfactory identifications despite a low spatial resolution (down to 2.1 samples per wavelength).