On the prediction of transmission loss of honeycomb panels: Experimental measurements and numerical simulations

Honeycomb panels are sandwich structures widely used in several fields, such as buildings transports and naval industry, due to their light-weight properties in combination with high bending stiffness. From an acoustic point of view, the mass decrease affects the vibro-acoustic performance of the panel and could result in unsatisfactory noise reduction properties. Then, an in-depth knowledge of the acoustic characteristics of the panel in terms of dynamic properties and transmission loss over frequency should already be achieved in the early stages of its design. This work focuses on the prediction of transmission loss for finite honeycomb panels, starting from the frequency response function of a bar. Experimental measurements are performed in free-free conditions in order to identify its resonance frequencies. Correspondingly, FEM numerical models simulating the bar 3d geometry and its dynamic strain, are set up and validated with the experimental results. Then the resulting dynamic properties are extrapolated over the frequency interval 50-5000 Hz and finally the sound reduction index of the finite-size honeycomb panel is predicted by combining wave propagation and standard thin plate theory. The comparison between the sound reduction curves simulated numerically and measured experimentally in a double reverberation chamber (ISO 10140-1 and ISO 10140-2) shows a fair agreement over the whole frequency range. Thus, the FEM model can be successfully used to perform preliminary parametric analysis and to optimize the honeycomb panel sound insulation properties according to specific applications. For its application the method only requires the knowledge of the detailed panel geometry and of core and laminates mechanical properties.