Spider orb web, investigating structural features and using biomimicry for lattice design

Abstract

Spider orb web has evolved to fulfil multiple roles, such as catching prey and acting as a sensing tool. For orb-weavers, the web must stop and retain prey, which can fly into it with considerable momentum. Considering orb weaver spiders are mostly blind, the web must also transmit accurate information about the prey’s location. There are many web features aiding these roles; some are known, and some are waiting to be shed light on. Considering these two cases, there are also two parts in this thesis, the first part is about a particular web-building behaviour of spiders and how it affects the signal transmittance, and the other is about creating a new lattice design for energy absorption utilizing some of the known structural characteristics of the spider web. The first part of this study is about designing a new lattice (SW) for energy absorption inspired by the structure of spider webs. Spider orb web comprises four structural elements: anchor, frame, radial, and spiral threads. The first three are the main components that provide structural integrity. These components have a hierarchical nature; the anchors bind to the environment and are generally thickest, while radii form the innermost part with the thinnest threads. The frames make up the connection between the anchor and radii; thus, there is no direct connection between them, and they generally have a thickness value between the radii and anchor threads. These features help the spider orb web to be a resilient, efficient structure for energy absorption, so using the same properties, a 3D lattice was designed for energy absorption. This design is then optimized for improved Energy Absorption Efficiency(EAE) and Energy Absorption(EA) value. The second part is about web-building behaviour that seems counterintuitive, heavier spiders increase the pretension of the threads as they get heavier, which diminishes the ability of the web to stop and retain prey. To investigate this behaviour, a spider web model with controllable pretension is needed; thus, a pretension-adjusting algorithm has been developed. A realistic spider web model was created using non-linear material properties to describe the mechanical behaviour of the spider silk and web pretension values seen in nature. Using this model, different scenarios with changing spider weight and web pretension were simulated using a numerical method based on Solid Mechanics. Our results show that this behaviour is likely related to the signal transmittance on the spider web. Spider web evolved to withstand damaging environmental factors such as wind and rainfall while preserving its functionality for trapping prey. Understanding spider web structure could lead us to improve engineering designs by implementing similar resiliency. This thesis presents a study investigating spider webs and a biomimicking application inspired by spider web structure. So, while the two areas are different in the sense that one is closer to biology while the other is to mechanical engineering, they serve the same purpose: understanding how this structure, spider orb-web, functions and how we can take ideas from it.