Abstract
Origami bellows are hollow cylindrical structures folded from flat sheets along predefined creases. Origami bellows such as Kresling and Miura-ori patterns are shown to exhibit multiple stable configurations. Multistability enables origami to deploy from a relatively compact stable state to a more expanded functional state, making origami bellows promising candidates for mechanical metamaterials, deployable space habitats etc. To design bellows with desired functionality, accurate numerical models are essential. For simplicity, current models generally ignore manufacturing details, and their influence on the mechanical properties has rarely been studied. The exploration for considering manufacturing details led to the discovery of an additional stable state in the Kresling bellow. However, the transition between these stable states, including the changes in geometry and mechanics, remains unexplored. Hence, this thesis aims to provide a better understanding of origami bellows from different aspects, including the influence of manufacturing details, and the change in geometry and mechanical properties between stable states.First, the effect of small cut-outs at the vertices — a common manufacturing detail to alleviate stress concentrations — on the mechanical properties of the origami bellows is examined under axial compression. A high-fidelity finite element model is developed to carefully capture the size of cut-outs and compared against experimental measurements. Two representative non-rigid foldable bellow patterns are examined: the Miura-ori bellows consisting of quadrilateral facets and Kresling bellows consisting of triangular facets. The results show that the introduction of cut-outs at the vertices will lead to a significant change in mechanical properties as well as nonlinear responses, such as axial stiffness, limit force, the existence and position of stable state. The effect of cut-outs is observed across the geometric design space, and using different modelling methods for the creases such as torsion springs and smooth folds. These results have wider implications for the non-rigid foldable origami patterns in general. In this study, it was found that the bistable Kresling pattern has an additional stable state by popping the short diagonals outwards. However, the changes in geometry and mechanical properties between three stable states remain unexplored.
Next, the geometric change of the tristable Kresling bellows between its three stable states is studied based on geometric models. This pattern is compared against the bistable Miura-ori bellows, and their application as deployable space habitats is examined. Calculation methods for internal volume and effective volume for both bistable Miura-ori and tristable Kresling bellows are proposed, in order to determine the change in volume between different stable states. A multi-objective optimisation is used to find patterns with a high volume deployment ratio under specified geometric and manufacturing constraints (e.g. rocket fairing
dimensions and wall thickness). The results show that both two patterns can offer significant volume increases compared to conventional cylindrical habitats that have no volume increase. Specifically, the Kresling pattern can achieve a volume expansion ratio of 2.56, while the Miura-ori pattern can reach a ratio of 8.31 but at the expense of a large change in diameter which will bring challenges for the design of airtight habitat.
Finally, the change in mechanical properties of the tristable Kresling bellows between stable states is studied and extended to the conical Kresling pattern. First, the existence of geometric tristability is demonstrated, and the additional stable state is added to geometric design maps. Different design maps (e.g. based on intrinsic or extrinsic geometric parameters) provide complementary insights, and thus a mapping between commonly used maps is introduced to aid the design of origami bellows. Using a reduced-order mechanical model, the change in axial stiffness between different stable states is studied across the full design space, to reveal a high axial stiffness at the additional stable state. Twisting is chosen as the actuation method to trigger the transition between different stable states. The transition process can be simulated both by the reduced-order mechanical model and finite element models. Nevertheless, the reduced-order mechanical model can only provide a qualitative validation while finite element model is capable of capturing more details such as local buckling. Physical prototypes are manufactured to validate the transition process simulated by numerical models.
In essence, this thesis advances the understanding of multi-stable origami bellows by highlighting the significant influence of manufacturing details, demonstrating the limitations of reduced-order mechanical models, showing the significant volume expansion ratio of Kresling and Miura-ori patterns, and exploring the mechanics of tristable Kresling bellows.
| Date of Award | 4 Feb 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Mark Schenk (Supervisor) & Fabrizio Scarpa (Supervisor) |