Bionic Study On The Damping Vibration Characteristic Of Long-eared Owl Primary Feather

Strigiformes bird features unique noise reduction characteristic to make itself flying silently through millions of years of natural selection and biological evolution. Owl's silent flight mechanism research has important instructive significance to the exploration of new principle and new technology of noise suppression, and cleaning up of the noise pollution in engineering.In this thesis, long-eared owl was studied as the main object and compared with golden eagle and pigeon to further reveal the nioseless flight mechanism of strigiformes animal and promote the bionic material research. Geometrical morphology, viscoelastic damping property and vibration attenuation characteristic of the cross-scale multiple branches in the primary feather were quantitatively characterized and compared between the three birds. In addition, allometric scaling model was adopted to describe the relationships between the geometrical characteristics and material properties of the cross-scale multi-branched structures on long-eared owl primary feather. Meanwhile, mechanical parameters and damping property of the SU-8 photoresist polymer to be used for the structures and devices with vibration control requirements in the Micro-Electro-Mechanical Systems (MEMS) were studied. The purpose was to provide a theoretical basis for the design and manufacture of the bionic noise reduction structure or device in MEMS. The main researches and achievements covered in this thesis are summarized as follows:(1) Multiple branches in the long-eared owl, golden eagles and pigeon primary feathers were morphological characterized. Observation results indicated that long-eared owl primary feather was equipped with uniform slender barbicels and barbules, narrow curled ventral margin in its barbs. Geometry parameters results of the multi-branched structures in primary feathers suggested that with a constant branching angle of 44.3°, length-diameter ratios of the long-eared owl feather branches were larger than those of golden eagles and pigeon feathers.(2) Viscoelastic damping properties of the multi-branched structures on the three birds' primary feather were characterized. Instron 3345 single column test system and a developed micro-tensile testing system, were applied to investigate the rachises, barbs and barbules of the three birds'primary feathers under a constant uniaxial tensile rate. Viscoelastic mechanical behavior of the feather material during the tensile process was described by a standard linear solid model. In adittion, viscoelastic parameters (E1, E2, ?) and the material loss factor (tan ?) were calculated. It was found from the comparative study that among the three kinds of primary feathers, long-eared owl primary feather had branch structures with the most excellent material damping performance.(3) Vibration suppress characteristic of the three birds'primary feathers and their barbs was studied. Free vibration tests were conducted based on the precision displacement measurement and high-speed camera technology, respectively. And damping ratio (?e) of the three kinds of whole feathers and barbs were calculated from the free vibration curves. The results showed that damping ratio values of both the whole long-eared owl primary feather and its barb structure were higher than those of golden eagles and pigeon primary feathers and their structures. Therefore, more vibration energy would be dissipated for long-eared owl primary feathers during the wing waving, thereby mechanical noise due to the mechanical oscillation and friction of the feather structures and aerodynamic noise caused by air disturbance around the feather structures would be suppressed.(4) Allometric scaling relationship of the multi-branched structures in long-eared owl primary feather was investigated. Geometry parameters measurements of the multi-branched structures showed that allometric scaling model could be applied to describe the geometry relationship of the branching diameters and lengths for three kinds of primary feathers. Meanwhile, relationship between the material properties (E1,?) and branching lengths of the cross-scale multi-branched structures on long-eared owl primary feather were established by the allometric scaling model to provide a basis for bionic material design.(5) Mechanical parameters of SU-8 polymer double-clamped beams with 12 different aspect ratios were characterized on a self-developed micro-tensile testing system. The experimental results suggested that the effective aspect ratio was a significant factor mechanically charactering the size effect of Young's modulus and maximum strain of SU-8 photoresist in micro-scale and could be used as a reference for biomimetic design. Besides, DMA tests were carried out for the damping performance study of the SU-8 rectangular thin film. The results showed that material loss factor of the SU-8 film was 0.08-0.21 in the temperature of 75??150?. In future study, material modification of SU-8 polymer may contribute a lot to improving its damping performance and mechanical property, thus providing a theoretical basis for the design and manufacture of across-scale,especially the micro-scale structure with damping vibration characteristic.