Wang Bin, Meyers Marc André
Materials Science and Engineering Program Department of Mechanical and Aerospace Engineering University of California San Diego La Jolla, CA 92093 USA.
Adv Sci (Weinh). 2016 Dec 1;4(3):1600360. doi: 10.1002/advs.201600360. eCollection 2017 Mar.
Only seldom are square/rectangular shapes found in nature. One notable exception is the bird feather rachis, which raises the question: why is the proximal base round but the distal end square? Herein, it is uncovered that, given the same area, square cross sections show higher bending rigidity and are superior in maintaining the original shape, whereas circular sections ovalize upon flexing. This circular-to-square shape change increases the ability of the flight feathers to resist flexure while minimizes the weight along the shaft length. The walls are themselves a heterogeneous composite with the fiber arrangements adjusted to the local stress requirements: the dorsal and ventral regions are composed of longitudinal and circumferential fibers, while lateral walls consist of crossed fibers. This natural avian design is ready to be reproduced, and it is anticipated that the knowledge gained from this work will inspire new materials and structures for, e.g., manned/unmanned aerial vehicles.
自然界中很少能发现方形或矩形形状。一个显著的例外是鸟类羽毛的羽轴，这就引出了一个问题：为什么近端基部是圆形的，而远端却是方形的？在此发现，在相同面积下，方形横截面具有更高的抗弯刚度，在保持原始形状方面更具优势，而圆形截面在弯曲时会变成椭圆形。这种从圆形到方形的形状变化增加了飞行羽毛抵抗弯曲的能力，同时使沿羽轴长度的重量最小化。羽轴壁本身是一种异质复合材料，其纤维排列根据局部应力要求进行调整：背侧和腹侧区域由纵向和周向纤维组成，而侧壁由交叉纤维组成。这种天然的鸟类设计有望被复制，预计从这项工作中获得的知识将激发例如载人/无人飞行器等新材料和结构的灵感。
