Abstract
Flight feather shafts are outstanding bioinspiration templates due to their unique light weight and their stiff and strong characteristics. As a thin wall of a natural composite beam, the keratinous cortex has evolved anisotropic features to support flight. Here, the anisotropic keratin composition, tensile response, dynamic properties of the cortex, and fracture behaviors of the shafts are clarified. The analysis of Fourier transform infrared (FTIR) spectra indicates that the protein composition of calamus cortex is almost homogeneous. In the middle and distal shafts (rachis), the content of the hydrogen bonds (HBs) and side-chain is the highest within the dorsal cortex and is consistently lower within the lateral wall. The tensile responses, including the properties and dominant damage pattern, are correlated with keratin composition and fiber orientation in the cortex. As for dynamic properties, the storage modulus and damping of the cortex are also anisotropic, corresponding to variation in protein composition and fibrous structure. The fracture behaviors of bent shafts include matrix breakage, fiber dissociation and fiber rupture on compressive dorsal cortex. To clarify, ‘real-time’ damage behaviors, and an integrated analysis between AE signals and fracture morphologies, are performed, indicating that calamus failure results from a straight buckling crack and final fiber rupture. Moreover, in the dorsal and lateral walls of rachis, the matrix breakage initially occurs, and then the propagation of the crack is restrained by ‘ligament-like’ fiber bundles and cross fiber, respectively. Subsequently, the further matrix breakage, interface dissociation and induced fiber rupture in the dorsal cortex result in the final failure.
Highlights
In recent years, fiber-reinforced plastic (FRP) has been proven to be light, stiff and strong [1]
The flexural behaviors and properties of feather shafts are tested by three-point bending tests, and a non-destructive technique for damage detection, acoustic emission (AE) [31,32,33,34], is simultaneously applied to monitor the realtime damage of specimens, further revealing the damage patterns and relevant fracture mechanisms of bent shafts
The results indicate that the storage modulus of dorsal cortex is increased from calamus to distal shaft (Figure 5a) and is gradually reduced in lateral cortex (Figure 5b)
Summary
Fiber-reinforced plastic (FRP) has been proven to be light, stiff and strong [1]. The feather shaft potentially exhibits a natural design strategy for thin-walled composite beams facilitating flight; it is of paramount importance to unravel the composition and mechanical behaviors of feather shafts. The feather shaft potentially hibits a natural design strategy for thin-walled composite beams facilitating flight; it i paramount importance to unravel the composition and mechanical behaviors of feat shafts. In a bid to address the issues mentioned above, this work provides a systematic study of the anisotropic cortex of the eagle feather shaft, correlating to the features involving the design of bioinspired composites with novel thin-walled structures. The flexural behaviors and properties of feather shafts are tested by three-point bending tests, and a non-destructive technique for damage detection, acoustic emission (AE) [31,32,33,34], is simultaneously applied to monitor the realtime damage of specimens, further revealing the damage patterns and relevant fracture mechanisms of bent shafts. Our findings and analysis intend to reinforce our understanding of the eagle feather shaft and stimulate the design of novel synthetic structures that can reproduce the remarkable properties of the flight feather shaft
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