Mechanics in naturally compliant structures

摘要

In this study the mechanics of compliant structures (very light weight structures which do not have bending capability but have axial stiffness (tension)) in particular to spider web has been studied. The orb-web spider has evolved over the last 180 million years [Lin, L.H., Edmonds, D.T., Vollrath, F., 1995. Structural engineering of an orb-spider's web. Nature 373, 146-148]. This long period of evolution has produced the present spider web, an elegant, natural, lightweight structure to efficiently resist different loads such as wind, insect impact, etc. It can function as a net for catching prey even if any element is broken. Nature has accomplished these tasks by optimizing its form of construction, and by making spider silk a biopolymer with superior elasticity and tensile strength. It is believed that spider webs are the most efficient structures engineered by nature. In this study it is tried to find why spider webs are so efficient. A FE model of an ideal spider web has been created using the FEMAP pre- and post-processing software, and analyzed using the ABAQUS non-linear FE code. Both the static and dynamic problems have been considered, and also the numerical and experimental techniques have been used. It has been tried to look at how stress is redistributed in the face of damage and how the loss of elements affects the dynamic response of the web and how the vibration due to insect impact is damp out. Finally the numerical simulations have been compared to physical experiments. In lieu of actual spider webs, artificial nets have been examined and its 1st natural frequencies for different cases have been measured by laser vibrometer. A FE model of the net has also been created in FEMAP and analyzed by ABAQUS. In both analyses, the same elements have been removed systematically from the center and the 1st natural frequencies have been determined. Prediction matches well with experiment. The results of this study may be used in light structures like cable-stayed bridges [Masura, M., Yokoyama, K., Toshio, M., 1989. Wind-induced cable vibration of cable-stayed bridges in Japan. In: Proceedings of Canada-Japan Workshop on Bridge Aerodynamics, Ottawa, pp. 101-110; Yoshimura, T., Inoue, A., Kaji, K.K., Savage, M.S., 1989. A study on the aerodynamic stability of the Aratsu Bridge. In: Proceedings of Canada-Japan Workshop on Bridge Aerodynamics, Ottawa, pp. 41-50] and space structures.