Free Wave Propagation in Sandwich-Panels with Poro-Elastic Cores

摘要

Free wave models for sandwich panels with either anisotropic poro-elastic or solid cores werernimplemented, and the wave motions were decomposed into symmetric and antisymmetric forms to clarify the wave behavior in the three-layer sandwich configuration. By deriving the Rayleigh-Lamb frequencyrnequation for a plate from the anisotropic solid core model, the procedure for formulating the characteristicrnequations used in this work was verified. From the dispersion equations, the complex wave numbersrnwere numerically identified and were visualized as a function of frequency. For the baseline panels, itrnwas found that a coincidence frequency occurred at 11 kHz, i.e., when the symmetric mode first began tornpropagate, which resulted in a TL drop. It was found that a TL reduction can result from a coincidencernfrequency caused either by the first appearance of the symmetric mode or when the first antisymmetricrnmode transitions from subsonic to supersonic. A parametric variation study was used to show that it isrnpossible to predict the effect of adding mass or altering the core shear stiffness on the sandwich panel TLrnperformance. It was found, in particular, that altering the core shear stiffness or varying the facing platernthickness were the most effective means of controlling the TL of sandwich panels of the type consideredrnhere.