Damage Tolerance in Naturally Compliant Structures

ABSTRACT: In this study, the damage tolerant design in a particular compliant structure, the spider web, has been studied. The orb web spider has evolved over the last 180million years. This long period of evolution has made the present spider web, an elegant, natural, lightweight structure that efficiently resists different loads, such as wind and insect impact. It can function as a net for catching prey even if several elements are 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. Spider webs are clearly one of the most efficient structures engineered by nature. In this study, we attempt to understand how the spider web achieves its damage tolerance. A finite element (FE) model of an ideal spider web has been created using the FEMAP pre- and post-processing software and analyzed using the ABAQUS nonlinear FE code. Both the static and dynamic problems have been considered, and experimental validation has also been performed. How stress is redistributed in the face of damage and how the loss of web elements affects the dynamic response of the web have been considered. Finally, the numerical simulations have been compared to physical experiments. Instead of actual spider webs, artificial nets have been examined; the first natural frequencies for different damage configurations 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 of the web and the first natural frequencies have been determined. The predictio