Experimental modal based vibro-acoustic analysis of sandwich panels

Experimental modal analysis techniques are used to compute conductance, vibration energy, and damping loss factors of a stiff lightweight sandwich panel. The panel, constructed from honeycomb core and carbon fiber face sheets, was tested with a shaker, force hammer, and surface-mounted accelerometers. The extracted modal parameters are used to reconstruct panel conductances and surface vibration frequency response functions, filtering out measurement error effects. The modal parameters are also used to exactly compute vibrational energies, even for structures with spatially inhomogeneous mass distribution. The modal energies are confirmed by comparing loss factors inferred using the Power Injection Method (PIM) to those measured directly from the modal analysis, and from decay-based measurements. Finally, radiation damping is computed using an acoustic boundary element (BE) model applied to the measured vibration fields. The radiation damping peak near the panel critical frequency matches the total measured damping nearly exactly, and may be subtracted from the total damping to infer in-vacuo structural damping.