Development of construction methods and synthesis of manufacturing technologies for the production of cellular plastic hybrid structures for applications in sound absorbers

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As the volume of traffic increases, there is a demand for a significant reduction of the radiated sound power. Helmholtz resonators (HR) are used as sound absorber in the mobility sector, for example in the form of sandwich constructions, so-called HR liners. These absorbers consist of a base layer, a perforated face sheet and an intermediate cavity structure. Due to their physical principles, the damping effect of such resonators is limited to a narrow frequency range. Therefore, they cannot be used for efficient attenuation of broadband noise. A promising approach to widening and increasing the absorption characteristics of such HR liners is the use of honeycomb-like cavity structures with partially flexible cell walls. These walls are excited to damped vibrations by pressure changes of the airborne noise and thus dissipate acoustic energy. Due to their low density and thickness as well as their high material damping, thermoplastic plastic films are particularly suitable for these flexible cell wall areas. By providing a cellular plastic hybrid structure, which contains not only flexible cell walls but also pressure and shear resistant cell walls, the damping effect and the sandwich structure’s compressive strength in the thickness direction are ensured. The combination of thermoplastic films with partially applied, unidirectionally reinforced, thermoplastic tapes represents a promising approach. The conceptually planned process line for the technical production realization of these structures includes not only the tape application but also the process steps of partial cutting, contouring and folding.Within the scope of this research project, construction concepts for cellular plastic hybrid structures with flexible and rigid cell wall areas for novel HR liners are being developed for the first time and analysed in terms of structural mechanics. For these structures, the conceptual development of a process chain is to be carried out by technology synthesis and the kinetostatic analyses of the individual sub-processes for preliminary design. For this purpose, suitable materials and semi-finished products for the reinforced and unreinforced cell wall areas are selected and characterized. Based on this, application, cutting, profiling and folding technologies for the production and further processing of fiber-reinforced tapes on thermoplastic films are developed and tested. Finally, the HR liner demonstrators are evaluated from a geometric and structural-mechanical point of view. The production technology investigations are the basis for the development of a serial production process of plastic hybrid structures for use in sound absorbers.