Impact of Foaming Baffle Materials on Structure Borne Noise in Car Bodies

Foaming materials such as 2C-PUR or expandable baffles are increasingly used in the car body acoustic package of modern passenger vehicles. Over the last several decades the primary function of foaming materials was the moisture sealing and airborne noise absorption / insulation in various areas of the car body such as pillars, door sills or other cavities. Recent developments also show an increasing application of expandable foams, functioning as structural dampers and reducing structure-borne noise transmission through frames and pillars. This paper summarizes the results of various studies that deal with the impact of expandable baffle materials on structure-borne noise in car bodies with special focus on mid and high frequencies which become more relevant in the acoustic optimization efforts of EV’s. Structural vibrations are evaluated experimentally on foamed generic frames and double sheet metal systems under free-free boundary conditions. The most promising candidate among tested foaming materials is then introduced into a C-Segment car body. This body is investigated with laser scanning vibrometry and transfer functions are measured using dual shaker excitation. The presented results are showing potential damping performance of baffle foams compared to empty body and bodies damped with conventional liquid-applied-sound-dampers and bitumen foils.