Highly multi-stable FRP grids for shape adaptation

Multi-stability in lightweight structures has been the subject of intensive research. This property is advantageous for the realization of shape adaptable structures because it allows, for example, maintaining different configurations of the structure without the presence of a continuous power supply. However, the integration of multi-stable components into complex structures is not widely implemented yet due to high coupling between the stable modes, suppression of stable modes due to the influence of boundary conditions, and complex fabrication techniques. In this work, a novel class of highly multi-stable periodic structures is presented. The investigation is first conducted on a single cell structure that possesses eight stable modes and, second, expanded to grid structures with periodicity. The multi-stability of the unit cell is preserved in the periodic structures and, in fact, the grid possesses further stable configurations not observed in the unit cell. Prototypes are fabricated by combining flat thin fiber-reinforced polymer (FRP) composite frames with bi-axially pre-stretched membranes. Therefore, the proposed approach enables the fabrication of highly multi-stable FRP grids without the need of a mold. Finite element analysis and experimental results show that the multi-stability property depends on the level of anisotropy of the laminate employed. Highly anisotropic laminates strengthen the multi-stability while isotropic ones suppress it. The realization of such highly anisotropic components with additive manufacturing techniques such as 3D-printing has been proved to be feasible, enlarging the range of materials suitable for the proposed concept. The presented technique is expected to be advantageous for the realization of highly reconfigurable, yet foldable, space habitats and antennas.