The damping properties of the foam-filled shaft of primary feathers of the pigeon Columba livia

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.

Analysis and comparison of protein secondary structures in the rachis of avian flight feathers

“…Interestingly, round or elliptical shapes of the cortex of flight feather rachises of sacred ibis and owls were identified. Furthermore, a foam-like medulla filled in the hollow space of the cortex of these flight feathers ( Lingham-Soliar, 2017 ; Wang & Meyers, 2017 ; Chang et al, 2019 ; Deng et al, 2021 ). The morphological structures of the flight feather medulla differ among these species; for example, the structure in the medulla in the flight feathers of sustained flyers and birds of prey shows a V-ridge shape, and the characteristic hollow shape is observed on the dorsal part of the medulla, suggesting that the organization of the medulla is critical for providing mechanical support ( Chang et al, 2019 ).…”

Aerodynamic vs. frictional damping in primary flight feathers of the pigeon Columba livia

“…The interior part of the barbs is filled with gradient foams [18]. This foam structure undergoes plastic deformation, which contributes to energy dissipation, similar to the damping in the shaft medulla [15]. However, the contribution of the material damping is the lowest if compared to the two mechanisms mentioned above.…”

“…The loss factor is in the range of 0.03-0.07 for the bending of the shaft of swan feathers [13] and 0.896 ± 0.238 for the shafts of pigeon feathers [14]. The damping ratios of pigeon feather shaft regions gradually decreased from the base to the tip from 0.268 to 0.034 [15].…”

The Role of Vanes in the Damping of Bird Feathers

“…Material damping refers to inherent energy dissipation during material deformation [42]. The shaft and vanes elements of the feather are filled with a foam medulla, which was shown to effectively damp vibrations [28].…”

“…The loss factor of single pigeon primary feathers (0.1573, 0.093 vertically, and 0.0912, 0.0709 parallelly) and single barb (0.0790 vertically, and 0.1234 parallelly) [27]. The different shaft regions of the pigeon feathers under deflections were investigated, and graded damping properties from base to tip were found (from 0.268 to 0.034) [28].…”