Journal of Bionic Engineering(2008)Vol 5 No. 3 scientific and engineering inventions and innovations organisms, could be extracted and applied to optimize are obtained. After several billion years of evolution, the the mechanical design process, and material-efficient structures of organisms have developed excellent prop- structures could be derived to improve the load-bearing erties and ingenious frames, which provide innovative behavior of the structural component prototypes approaches for solvin neering problems and improving design. Successful bionic designs in other fields can be used for further research on characteristics of biological structures and their application in mechanical design. This new method breaks through the traditional design mode and will create products with better performance and lighter structure 2 Cylindrical structures in nature and Fig. 2 Cross-section of plants: (a) Brazilian Giant Horsetail;(b) engineering Dutch Rush 9] Thin-walled cylindrical structures are found widely 3 Buckling of cylindrical shells in both engineering components and nature. The typical ratios of shell radius to thickness of a variety of cylin- 3.1 Buckling problems of cylindrical shells drical engineering structures can be seen in Fig. 1. In A cylindrical shell is shown in Fig. 3 with one end some applications, such as space shuttle fuel tanks, air- simply supported, which bears an axial uniform pressure craft fuselages, and offshore oil platforms, the ratio of P, and the other end clamped. The axially compressed load bearing to weight is an essential element of design. cylindrical shell can fail either by global buckling with a In nature, thin-walled cylindrical structures are often wavelength related to its length, or by local buckling supported by a honeycomb or foam-like cellular core with a wavelength related to the shell thickness, or by the that increases the resistance to buckling, for example, in yielding of the material of the shell. So the ratio of radius plant stems(Fig. 2), porcupine quills, or hedgehog to thickness determines the instability mode of the cy spines a) lindrical shell. In particular, when the thickness is rela- By analysis of macro and micro characteristics of tively small, the cylinder fails by local buckling( shown organisms, load-bearing structures'principles, which in Fig. 4 buckling shape B and C); while global buckling determine the excellent mechanical properties of occurs with a larger thickness(shown in Fig. 4 buckling Silos and,tanks nautical structures ofFshore oil structuref Biological structur ⊥⊥LLL LLL The ratio of radius to thickness g. 1 The ratio of radius to thickness a/t for typical engineering ylindrical structures/8 Fig 3 Cylindrical shell under axial compression232 Journal of Bionic Engineering (2008) Vol.5 No.3 scientific and engineering inventions and innovations are obtained. After several billion years of evolution, the structures of organisms have developed excellent prop￾erties and ingenious frames, which provide innovative prototypes and creative approaches for solving engi￾neering problems and improving design. Successful bionic designs in other fields can be used for further research on characteristics of biological structures and their application in mechanical design. This new method breaks through the traditional design mode and will create products with better performance and lighter structure. 2 Cylindrical structures in nature and engineering Thin-walled cylindrical structures are found widely in both engineering components and nature. The typical ratios of shell radius to thickness of a variety of cylin￾drical engineering structures can be seen in Fig. 1. In some applications, such as space shuttle fuel tanks, air￾craft fuselages, and offshore oil platforms, the ratio of load bearing to weight is an essential element of design. In nature, thin-walled cylindrical structures are often supported by a honeycomb or foam-like cellular core that increases the resistance to buckling, for example, in plant stems (Fig. 2), porcupine quills, or hedgehog spines[8]. By analysis of macro and micro characteristics of organisms, load-bearing structures’ principles, which determine the excellent mechanical properties of Fig. 1 The ratio of radius to thickness a/t for typical engineering cylindrical structures[8]. organisms, could be extracted and applied to optimize the mechanical design process, and material-efficient structures could be derived to improve the load-bearing behavior of the structural component. Fig. 2 Cross-section of plants: (a) Brazilian Giant Horsetail; (b) Dutch Rush[9]. 3 Buckling of cylindrical shells 3.1 Buckling problems of cylindrical shells A cylindrical shell is shown in Fig. 3 with one end simply supported, which bears an axial uniform pressure P, and the other end clamped. The axially compressed cylindrical shell can fail either by global buckling with a wavelength related to its length, or by local buckling with a wavelength related to the shell thickness, or by the yielding of the material of the shell. So the ratio of radius to thickness determines the instability mode of the cy￾lindrical shell. In particular, when the thickness is rela￾tively small, the cylinder fails by local buckling (shown in Fig. 4 buckling shape B and C); while global buckling occurs with a larger thickness (shown in Fig. 4 buckling shape A). Fig. 3 Cylindrical shell under axial compression