This paper deals with the effect of damping layers on vibration characteristics of cross-ply laminated, fiber reinforced plastics (FRP) thick plates with damping interleaves. For this purpose, the laminated plates are modeled by using the Multi-Layer (Individual-Layer) Theory. In this theory, a coordinate system is individually taken in each FRP layer or damping layer, and in-plane and out-of-plane displacements are assumed in the polynomial forms of third and second order, respectively. A set of governing equations for the whole laminated plate is derived from the equations of motion and other interfacial conditions. The free vibration and steady state vibration problems of the laminated plate are thus solved by the multi-layer theory. For comparison, an analysis is also presented by using the Lamination Theory, which uses only a single displacement field for the whole plate. Natural frequencies and steady state responses are calculated in numerical examples for the plates with various stacking sequence and thickness ratios of damping layers to FRP layers, and the effects of location and thickness of the damping layers on vibration characteristics are studied. Furthermore, the applicability of both the multi-layer and the lamination theories in the vibration analysis is discussed by comparing two sets of results.
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