Transmission loss variation of mass constant sandwich plates using geometric honeycomb core variation

Abstract

Pollutant emissions like CO2 or NOX increased in the last decades. One reason is the increased av-erage distance covered by each person which has grown in a similar proportion. This again leads to the use of vehicles with combustion process more frequently. In order to counteract this trend, the government restricts the pollutant emission of new vehicles. One approach for efficient vehicles is the reduction of the transported mass. Lightweight structures such as sandwich composites offer the possibility of mass reduction with similar stiffness. Unfortunately, this leads to an increased sound radiation at lower frequencies. Therefore, insulating elements are necessary to reduce the sound transmission in the vehicle cabin, but this increases the mass and counteract the benefit of the light-weight structures. The example of sandwich plates will be used to show that the geometrical variation of a honeycomb core can increase the transmission loss. The core mass stays constant during this variation. The cell diameter of these cores varies between 5 cm and 13 cm, while commercially available cores have often diameters in millimeter range. The core variation is done with finite element analysis in the frequency range up to 2000 Hz. The transmission loss of selected sandwich plates is measured in order to confirm the simulation results. If the cell diameter size increases, the transmission loss in-crease can be shifted to lower frequencies. With a cell diameter of 13 cm the averaged increase of the transmission loss is by 3 dB and it starts by approximately 500 Hz. Thus, the design of a mass constant core improves the acoustic properties of a sandwich and it can address critical frequencies. Such acoustically adapted lightweight structures will reduce the number of insulating elements in vehicles. This design approach can contribute to lower the pollutant emissions of future vehicles.