Inverse Vibration Problem Used for the Characterization of the Damping Added by a Trim Foam on a Plate

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. With the help of FEA, it is possible to understand the influence of the damping effect. The implemented inverse methods are the Force Analysis Technique (FAT) and the Corrected Force Analysis Technique (CFAT), originally used for effort identification on a system. They are based on the motion equation of the system and the displacement field. In this study, these methods allow to determine the structural parameters, such as the elastic storage modulus and the loss factor.