Geometry and Elasticity Induced Bi-stability in a Cellular Structure with Star-Shaped Unit Cells

We introduce a novel family of origami-based structures with reversible foldability and bi-stability which relies on both properties of material and hinge characteristics. The proposed cellular structure is consisted of star-shaped bi-stable unit cells with two zero-energy states. Transition of the unit cells between two stable (zero-energy) configurations take place through elastic deformation of sub-components and hinge rotations. In this project, we prove bi-stability of unit cells experimentally and then investigate the effect of geometrical parameters on the existence and quality of bi-stability. The resultant unit cells can be designed to form different types of stars (three-pointed star, four-pointed star, and etc.) which also make difference in force-folding response of unit cells. Tiling star-shaped unit cells in three-dimensional space under different patterns forms various cellular structures with bi-stability transferred from underlying unit cells. The other interesting feature which arises from unit cell and transfers to cellular structure is auxeticity. Cross-section of unit cells under compressive load will be decreased gradually until it ends in second zero-energy configuration with smaller cross-section compared to first stable state.