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Modeling and experimental validation of a sandwich plate with isotropic face plates and viscoelestic core

We analyze and experimentally validate an analysis of a sandwich plate structure, where anisotropic face plates sandwich a viscoelastic core. Existing analytical models have been modified to incorporate piezo-actuation in anisotropic and 3-layered thin plates, using the variational energy method. The 3-layered sandwich consists of anisotropic face- plates with surface bonded piezo-electric actuators, and a viscoelastic core. The analysis includes the membrane and transverse energies in the face plates, and shear in the viscoelastic core. A constant, complex shear modulus was used for the dissipative core, thus frequency and temperature dependence of viscoelastic properties is neglected in this model. Simplified forms of the equations are stated based on neglecting shear in face-plates. Experiments were conducted on sandwich plates with aluminum face-plates under clamped boundary conditions to validate the simplified model. Symmetric and asymmetric sandwiches were tested. The maximum error in the first eight natural frequency predictions obtained via the assumed modes solution is less than 10%. Analytical studies on the influence of the number of assumed modes in the Galerkin approximation, and the core storage modulus variation, were conducted. The importance of the in- plane extension modes in sandwich plate analysis was demonstrated. Error in the first natural frequency is nearly 100% when in-plane modes are ignored; error reduces and converges to 6.7% as number of modes is increased to 16 in each of the in-plane directions for each face plate.