Abstract
The avian feather combines mechanical properties of robustness and flexibility while maintaining a low weight. Under periodic and random dynamic loading, the feathers sustain bending forces and vibrations during flight. Excessive vibrations can increase noise, energy consumption, and negatively impact flight stability. However, damping can alter the system response, and result in increased stability and reduced noise. Although the structure of feathers has already been studied, little is known about their damping properties. In particular, the link between the structure of shafts and their damping is unknown. This study aims at understanding the structure-damping relationship of the shafts. For this purpose, laser Doppler vibrometry (LDV) was used to measure the damping properties of the feather shaft in three segments selected from the base, middle, and tip. A combination of scanning electron microscopy (SEM) and micro-computed tomography (µCT) was used to investigate the gradient microstructure of the shaft. The results showed the presence of two fundamental vibration modes, when mechanically excited in the horizontal and vertical directions. It was also found that the base and middle parts of the shaft have higher damping ratios than the tip, which could be attributed to their larger foam cells, higher foam/cortex ratio, and higher percentage of foam. This study provides the first indication of graded damping properties in feathers.
Highlights
Flight has given the animals survival advantages, by providing efficient locomotion and various habitats (Clark 2013)
Wings consisted of the flight feathers needed to sustain the dynamic force and vibration during the flapping (Greenewalt 1960)
Excessive vibrations can lead to more consumed energy, noise, and negatively impact flight stability
Summary
Flight has given the animals survival advantages, by providing efficient locomotion and various habitats (Clark 2013). Wings consisted of the flight feathers needed to sustain the dynamic force and vibration during the flapping (Greenewalt 1960). It is reasonable to hypothesize that feathers of wings. Feathers originated in theropod dinosaurs as simple filaments of varying lengths and diameters (Clark 2013). In contrast, evolved into complex hierarchically organized epidermal structures (Prum 1999; Bragulla and Hirschberg 2003). Pennaceous vanes for flight and display, and fluffy plumulaceous branches evolved for thermoregulation (Chang et al 2019). Typical bird flight feathers consist of a shaft and two vanes (Fig. 1). The vane consists of numerous barbs aligned parallel to each other, but at some angle to the shaft (Prum 1999; Clark 2013). The barbs are loosely connected by the elaborate system of hooklets and, when separated by an external force, they can re-establish their connections (Ennos et al 1995; Butler and Johnson 2004; Kovalev et al 2013; Gao et al 2013; Chen et al 2016; Sullivan et al 2016)
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