1. Composite meta-structures for shape adaptation via multi-stability
- Author
-
Risso, Giada
- Subjects
- COMPOSITE STRUCTURES (STRUCTURAL ELEMENTS), ADAPTIVE STRUCTURES (ENGINEERING), Manufacturing, Engineering & allied operations
- Abstract
Adaptive structures are characterized by their ability to change their physical properties, behavior, or functionality in response to changes in the operating conditions or environment. The transition from conventional engineering de-sign to multifunctional and adaptable structures aims to enhance mechanical and energy efficiency, thus promoting a more sustainable future. Reconfigurable systems that can adjust their three-dimensional shape to optimize functionality and efficiency through shape transformation are a subclass of adaptive structures. To date, the key challenge when designing shape-adaptable structures is meeting the conflicting requirements of realizing large and reversible shape changes, while ensuring limited actuation effort, lightweight, and simple fabrication. This thesis addresses the current limitations by developing a novel de-sign approach that, for the first time, combines four design features already well-established in the research community: self-formation, mechanical meta-materials, multi-stability, and the two-way shape memory effect. Each of these features has individually led to significant research advancements. Their combination, as explored in this study, provides a path toward achieving remarkably versatile shape transformations. Herein, a metamaterial-inspired assembly of anisotropic components leads to reversible and actively controllable shape transformation together with self-locking capabilities. This thesis’s primary objective lies in exploiting the high anisotropy of thin fiber-reinforced polymeric (FRP) composite laminates to realize structures with a multitude of stable states. Main contributions cover novel manufacturing, modeling, and actuation strategies. First, a novel class of meta-structures is introduced, which combines pre-stretched membranes with flat FRP laminates. Leveraging the elastic strain energy of thin membranes, complex 3D topologies are achieved without elaborate fabrication routes. Second, accurate analytical and finite element models are developed to outline the design rules that enable shape-forming and multi-stability of the meta-structure. Results highlight the flexibility of the design approach: tailoring the 2D assembly of the FRP strips does not affect the multi-stability. Third, it is proven that the shapes can be actively controlled by selectively placing actuators onto the meta-structure. The actuation strategy is harnessed to realize a robotic surface with inchworm-inspired locomotion, demonstrating that multi-stable robotic surfaces exploit strong nonlinear mechanics to minimize actuation efforts. To conclude, integrating shape memory polymer membranes in the structures’ assembly eliminates the risk of undesired snapping to other stable shape under external loads. Results demonstrate that the meta-structures’ shape and stiffness can be tuned post-fabrication granting them to withstand 80 times their weight and to switch on and o˙ their multi-stability. Leveraging anisotropy of the materials and geometry is the fundamental innovation of the proposed design approach that realizes large multi-stable structures, with potential applications in reconfigurable space structures, adaptive greenhouses, wearable technologies, and soft robots. These meta-structures enable the realization of structural components that are no longer constrained to have a fixed configuration throughout their life span. This work contributes to the fabrication, design, and actuation of structures that can physically conform to their environment, adapt their stiffness to different operational modes, and change their shape to the users’ needs. This thesis proves that multi-stability is a powerful design tool, that enhances the functionality of adaptive systems, outperforming current solutions in terms of lightweight, shape reconfiguration, and energy efficiency. more...
- Published
- 2023