Harnessing the anisotropic multistability of stacked-origami mechanical metamaterials for effective modulus programming

This study examines a three-dimensional, anisotropic multistability of a mechanical meta material based on a stacked Miura-ori architecture, and investigates how such a unique stability property can impart stiffness and effective modulus programming functions. The unit cell of this metamaterial can be bistable due to the nonlinear relationship between rigid-folding and crease material bending. Such bistability possesses an unorthodox property: the arrangement of elastically stable and unstable equilibria are different along different principal axes of the unit cell, so that along certain axes the unit cell exhibits two force–deformation relationships concurrently within the same range of deformation. Therefore, one can achieve a notable stiffness adaptation via switching between the two stable states. As multiple unit cells are assembled into a metamaterial, the stiffness adaptation can be aggregated into an on-demand modulus programming capability. That is, via strategically switching different unit cells between stable states, one can control the overall effective modulus. This research examines the underlying principles of anisotropic multistability, experimentally validates the feasibility of stiffness adaptation, and conducts parametric analyses to reveal the correlations between the effective modulus programming and Miura-ori designs. The results can advance many adaptive systems such as morphing structures and soft robotics.