Acoustically Absorbing Lightweight Thermoplastic Honeycomb Panels

The aerospace industry has employed sandwich composite panels (stiff skins and lightweight cores) for over fifty years. It is a very efficient structure for rigidity per unit weight. For the automobile industry, we have developed novel thermoplastic composite panels that may be heated and shaped by compression molding or thermoforming with cycle times commensurate with automotive manufacturing line build rates. These panels are also readily recycled at the end of their service life. As vehicles become lighter to meet carbon dioxide emission targets, it becomes more challenging to maintain the same level of quietness in the vehicle interior.Panels with interconnected honeycomb cells and perforations in one skin have been developed to absorb specific noise frequencies. The absorption results from a combination and interaction of Helmholtz and quarter wave resonators. Computer modeling was used to design panels that absorb one of the problematic frequency ranges (800-1,250 Hz), caused by tires on the roadway. This was achieved in thin (7-8 mm) panels of low density (0.25-0.35 g/cc). Experimental results of acoustic absorption and transmission loss of polypropylene (PP) panels will be presented along with their mechanical performance.