Transmission loss adaption of sandwich panels with honeycomb core variation

Nowadays the primary and interior structures of modern transport aircrafts are of high stiffness and low weight. One example is the utilization of honeycomb sandwich panels which are used in cabin linings or nacelles. From an acoustic point of view such panels are disadvantageous because of the hollow core and the high stiffness to weight ratio. The core influences the sandwich stiffness at a minor level, but a core design change can affect the acoustic behavior more significant. Thus, within this paper a design tool will be presented which calculates a honeycomb core with a variable geometry and constant mass. This way it is ensured that the determined transmission loss variations are only due to the different honeycomb geometries. After the geometrical design the tool calculates the transmission loss via a harmonic finite element analysis. The results of the core variation clearly show an influence on the sound transmission. The eigenmodes of an exemplary sandwich shifted over 400 Hz with the core variation. Also, the amplitude of the transmission loss changes at these higher frequencies. For experimental investigations these honeycomb core geometries are realized by additive manufacturing. The honeycombs consist of plastic and the selected face sheets of glass fiber