Programmable Selfâ Locking Origami Mechanical Metamaterials

Abstract

Developing mechanical metamaterials with programmable properties is an emerging topic receiving wide attention. While the programmability mainly originates from structural multistability in previously designed metamaterials, here it is shown that nonflatâ foldable origami provides a new platform to achieve programmability via its intrinsic selfâ locking and reconfiguration capabilities. Working with the singleâ collinear degreeâ 4 vertex origami tessellation, it is found that each unit cell can selfâ lock at a nonflat configuration and, therefore, possesses wide design space to program its foldability and relative density. Experiments and numerical analyses are combined to demonstrate that by switching the deformation modes of the constituent cell from prelocking folding to postlocking pressing, its stiffness experiences a sudden jump, implying a limitingâ stopper effect. Such a stiffness jump is generalized to a multisegment piecewise stiffness profile in a multilayer model. Furthermore, it is revealed that via strategically switching the constituent cells’ deformation modes through passive or active means, the nâ layer metamaterial’s stiffness is controllable among 2n target stiffness values. Additionally, the piecewise stiffness can also trigger bistable responses dynamically under harmonic excitations, highlighting the metamaterial’s rich dynamic performance. These unique characteristics of selfâ locking origami present new paths for creating programmable mechanical metamaterials with in situ controllable mechanical properties.An origami mechanical metamaterial with programmable lockingâ induced piecewise stiffness is demonstrated. The kinematical and mechanical properties of the metamaterial can be strategically tuned by switching the deformation mode of the constituent cells between prelocking folding and postlocking pressing. The capabilities uncovered present new pathways for achieving programmability in metamaterials and metastructures.