Flexigami : folded polygonal unit cells for deployable metamaterials and mechanisms

Abstract

Deployable and transformable structures are of broad interest for applications including satellites and space exploration, temporary shelters, packaging, transportation, robotics and medical devices. One emerging approach to scalable fabrication of such structures involves the general concept of Origami-inspired design along with cutting, folding, and fastening of sheet materials. However, contrasting the classical approach of modeling Origami structures as having perfect hinges and rigid panels, consideration of the finite bending and rotational stiffness of these elements is essential to understand their constituent mechanics. Moreover, meta-materials and functional structures having fundamentally new mechanical properties can be designed this way. We present the design, fabrication and mechanics of a novel, deployable cellular material, which we call Flexigami. The unit cell takes the form of two parallel regular polygons, connected by a circuit of diagonally creased panels. Upon compression, individual unit cells transform either gently or abruptly between two stable equilibrium states depending on the interplay between hinge and panel properties. The mechanical behavior of each unit cell can be deterministically designed via geometry, dimensions and topology of the panels and hinges. Individual unit cells can collapsed reversible to less than 10% of their deployed volume. Within this transition regime, the force-displacement curve of each cell can be tuned to exhibit a smooth compression behavior or an instability followed by a self-reinforcing response. We use finite-element models complemented by analytical and computational analysis of the results to understand the importance of different mechanical properties of constituent hinges and panels and also demonstrate the fabrication of flexigami cells and mechanisms in various structural materials. Finally we present different mechanisms and their subsequent applications.