Damping of flexural vibration in the plane of lamination of elastic–viscoelastic sandwich beams

Laminated beams with internal viscoelastic layers are known to exhibit potentially high damping of flexural vibration in the direction normal to the plane of lamination. In this paper, a model is developed for vibration parallel to the plane of lamination of a symmetric five-layer elastic–viscoelastic sandwich beam. The model is used to study the resonant frequencies and damping ratios of the lowest several modes of beams with various boundary conditions and inertia and stiffness properties as the shear stiffnesses of the viscoelastic layers are varied. Experimental results for free–free beams with contiguous and segmented constraining layers are in reasonable agreement with the predictions of the model. icant damping can be attained in the lowest several modes in the plane of lamination of a sandwich beam if the boundary conditions on the principal and constraining layers differ. For the particular example of a partially covered cantilever with a square box-beam cross-section, it is found that a constrained-layer damping treatment whose mass is approximately 15% of the mass of the cantilever can produce loss factors larger than 0.07 in the first mode of vibration in both the direction normal to and the direction parallel to lamination.