Structure and mechanical behavior of a toucan beak
Structure and mechanical behavior of a toucan beak
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DOI：
10.1016/j.actamat.2005.04.048
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发表时间：
2005-12
期刊：
影响因子：
9.4
通讯作者：
Yasuaki Seki;M. Schneider;M. Meyers
中科院分区：
文献类型：
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作者：
Yasuaki Seki;M. Schneider;M. Meyers
巨嘴鸟的喙占鸟身长度的三分之一，但重量却只有鸟身重量的二十分之一。Toco巨嘴鸟（Ramphastos Toco）喙的结构是一种夹心复合结构，具有角蛋白的外部和由富含钙的蛋白质组成的封闭细胞纤维网络。角蛋白层由直径50μm、厚度1μm的六边形鳞片叠加而成。抗拉强度约为50MPa，杨氏模量为1.4GPa。显微和纳米压痕硬度测量证实了这些值。角蛋白壳表现出应变率敏感性，从低应变率（5×10−5/s）下有机胶释放引起的鳞片滑移过渡到高应变率（1.5×10−3/s）下鳞片断裂。闭孔泡沫由纤维组成，其杨氏模量是角蛋白壳的两倍，因为它们的钙含量更高。采用开孔泡沫和闭孔泡沫的Gibson-Ashby本构方程模拟了泡沫的压缩响应。通过实验和分析，建立了壳、泡沫和泡沫+壳的独立响应，证明了泡沫和壳之间存在协同效应。由Karam和Gibson开发的稳定性分析，假设一个理想的圆形截面，应用于喙。结果表明，泡沫通过提供弹性基础来稳定鸟喙的变形，从而增加了鸟喙在弯曲载荷下的火盆和屈曲载荷。
The toucan beak, which comprises one third of the length of the bird and yet only about 1/20th of its mass, has outstanding stiffness. The structure of a Toco toucan (Ramphastos toco) beak was found to be a sandwich composite with an exterior of keratin and a fibrous network of closed cells made of calcium-rich proteins. The keratin layer is comprised of superposed hexagonal scales (50μm diameter and 1μm thickness) glued together. Its tensile strength is about 50MPa and Young’s modulus is 1.4GPa. Micro and nanoindentation hardness measurements corroborate these values. The keratin shell exhibits a strain-rate sensitivity with a transition from slippage of the scales due to release of the organic glue, at a low strain rate (5×10−5/s) to fracture of the scales at a higher strain rate (1.5×10−3/s). The closed-cell foam is comprised of fibers having a Young’s modulus twice as high as the keratin shells due to their higher calcium content. The compressive response of the foam was modeled by the Gibson–Ashby constitutive equations for open and closed-cell foam. There is a synergistic effect between foam and shell evidenced by experiments and analysis establishing the separate responses of shell, foam, and foam+shell. The stability analysis developed by Karam and Gibson, assuming an idealized circular cross section, was applied to the beak. It shows that the foam stabilizes the deformation of the beak by providing an elastic foundation which increases its Brazier and buckling load under flexure loading.