Abstract: Even in this period of large expansion of active control for noise and vibration suppression, passive damping technology is widely accepted and used because of its low cost and high reliability in many common applications. Viscoelastic materials play an important role in vibration reduction both in their free and constrained layer forms. This paper addresses the problem of calculating the modal frequencies and loss factors of beams containing a constrained viscoelastic layer. The problem is approached from an analytical point of view and an approximation is proposed on the mode shapes to simply take into account different boundary conditions. Calculations are performed on the basis of the energy method and compared with the results of the classical RKU theory and a finite elements model. A similar approach is also adapted to the study of partially covered beams; in this situation the RKU theory doesn't fit and only the FE model has been used as reference. !6
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