Origami – Inspired Mechanical Metamaterials With Tunable Stiffness

A deployable structure is a structure that can reconfigure and change shape/size mainly from folding and unfolding, and has many applications from daily essentials (e.g., umbrella), vascular stents, to solar panels for spacecraft. Origami, the art of paper folding, thus naturally provides inspirations for deployable structures. Despite recent active research in origami and related deployable structures, a critical aspect of the origami research that has been overlooked is whether the deployed structure remains in a deployed state under loading, such as vibration experienced by a deployed structure used in spacecraft. From the perspective of mathematics of origami, deployability means the kinematics of the pattern geometry to deploy and collapse. Since this is a pure mathematic point of view, there is no energy associated with the deployability and collapsibility of the structure. Therefore, a deployable structure at the same time also allows it to collapse through which it deploys. Thus, easy deployment, one of the many attractive attributes of some origami patterns (e.g., Miura pattern and its derivates), also indicates that the structure can be easily collapsed. Here we create an origami-inspired mechanical metamaterial with on-demand deployability and selective collapsibility: autonomous deployability from the collapsed state and selective collapsibility along two different paths, with low stiffness for one path and substantially high stiffness for another path. The metamaterial is inspired by a triangulated cylinder pattern that has been studied as one type of deformable origami patterns. The created mechanical metamaterial yields unprecedented load bearing capability in the deployed direction while still possessing great deployability and collapsibility.

The lesson to create such a metamaterial can be greatly extended to other structures by achieving non-monotonic strain path, or in other words, deformable origami with interesting strain path. The key requirement for a general design principle would be two aspects, deformable origami and non-monotonic strain path. Though deformable origami was not extensively studied or discovered, one can create deformable origami patterns using rigid origami as the building block.

We believe that this work represents a new and innovative approach to create a mechanical metamaterial with on-demand and selective deployability and collapsibility and great stiffness and load bearing capability. The principle in this work can be utilized to design and create versatile origami-inspired mechanical metamaterials that can find many applications, ranging from deployable structures for aerospace, civil applications, implantable medical devices, daily essentials, and toys; bistable states for vibration isolations, to continuous tunable stiffness for wearable robotics.