MULTI-MATERIAL ADDITIVE MANUFACTURING OF MEMBRANE-TYPE UNIT CELL: INFLUENCE OF MATERIAL PROPERTIES ON RESONANT BEHAVIOR

Kurzfassung

Recent advances in multi-material additive manufacturing have enabled the fabrication of complex structures, such as metamaterials, leading to increased interest in their development and implementation. Membrane-type acoustic metamaterials are particularly attractive because they not only allow sound manipulation at low frequencies but also satisfy lightweight design requirements. However, fabricating these structures in a continuous and repeatable process still poses challenges. This difficulty arises primarily from the fact that each unit cell consists of a soft, pre-stressed membrane and a relatively rigid frame, which must be manufactured together in a precise and compatible manner. Multi-material additive manufacturing using the fused deposition modeling (FDM) method is a promising approach to address these challenges due to the availability of a wide range of flexible and rigid materials. Nevertheless, the material behavior involved in producing membrane-type unit cells requires further investigation, as the vibro-acoustic characteristics of the structure are governed by the membrane’s performance under pre-stress. In this study, membrane-type acoustic metamaterial unit cells are fabricated using multi-material FDM printing. Flexible thermoplastic polyurethane (TPU) materials with varying hardness levels and thicknesses are used in combination with a relatively rigid polyethylene terephthalate glycol (PETG) material. The frequency response of the membrane displacement is measured using a laser Doppler vibrometer under acoustic excitation. The pre-stress magnitudes are estimated based on the assumption that pre-stress is present in the membrane and that the structure contains no fabrication defects. Subsequently, a finite element model is developed, and the results are compared with experimental data. Finally, the influence of flexible material hardness and membrane thickness on both the fabrication process and the performance of the unit cells is discussed.