Tutorial on the vibroacoustics of composite sandwich panels

Composite sandwich panels are used throughout the aerospace industry as lightweight, stiff structural components. While the vibroacoustic behavior of simple isotropic homogeneous panels are described in many textbooks and articles, the properties of composite sandwich panels are not as well documented. This tutorial describes basic analytic methods for estimating sandwich panel wavespeeds, modal frequencies, mobilities/conductances, and radiation resistances. Measured and simulated data from two example sandwich panels - a launch vehicle panel with free boundaries and a framed rotorcraft roof panel with simply supported boundary conditions - are shown to illustrate these concepts. Modal wavenumber analysis confirms the wavespeed estimating procedures. Mobility/conductance becomes dominated by shear waves at fairly low frequencies. Finally, the strong contribution of radiation damping to overall modal damping is evident in measured data.