Abstract
Bistable shells can hold two configurations by their own mechanical properties and this is well demonstrated by Venus flytrap which feeds herself as a plant in nature. Various methods based on different bistable mechanisms have been proposed to achieve bistable shells, however, there is no applicable method to build multistable shells, especially with designable configurations and good stability.Nanotechnology, Surface Mechanical Attrition treatment (SMAT), is proposed and applied, through special controllable treatments, to build multistable shells with designable configurations and good stability in this thesis. Theoretical and experimental works have been done for analysis and design of the achieved bistable and multistable shells, and aerodynamic experiments have been conducted to demonstrate the potential application of the developed multistable shells for various structures involving shape adaptations.
Firstly, bistable square shells are manufactured using SMAT, which are proved to have much enhanced stability compared with conventional bistable shells. Analytical models, in contrast to numerical models adopted for conventional bistable disks, are formulated for the nanostructure induced bistable disks to demonstrate the new bistable mechanism, validated by experiments using 304 stainless steel disks. Six different types of transitions for bistable disks are identified analytically. Analytical models and numerical models are developed for bistable rectangular shells with a rectangular and an elliptic nanostructured region, respectively, whose results are validated by experiments. The configurations and load bearing capacities of the proposed bistable shells can be designed to some extent by selecting the shape and dimension of the nanostructured region and the further applied treatment. In addition, experiments with bistable shells subjected to thermal treatment clearly show that the nanostructure induced bistable or multistable shells can sustain high temperature, unlike any existing bistable shells.
Multistable shells are manufactured by nanostructuring multiple local regions in one plate. The configurations of the multistable shells can be designed by the shapes and dimensions of the multiple nanostructured regions, the applied treatments and their distributions. Experiments have been done for multistable shells with nanostructured regions distributed in a row form and matrix forms, whose stable configurations are successfully predicted by the developed numerical models. Also, configurations of the nanostructure induced multistable shell can be further modified by plastically bending.
To prove the feasibility of the developed multistable shells for applications of structures involving shape adaptations, two aerodynamic experiments have been conducted in wind tunnels, whose visualization and measured quantitative results clearly demonstrate that the aerodynamic responses of the built structures are adjustable via the various configurations of the utilized multistable shells. The developed method provides an effective technique to build morphing structures with high efficiencies.
| Date of Award | 5 Jul 2016 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Xiaoqiao HE (Supervisor) |