An Origami-inspired Mechanical Metamaterial with Graded Stiffness

Origami-inspired mechanical metamaterials are often made up of individual repeat units, the folding and relative geometry of which determine the overall material properties. If these units are identical, then the mechanical properties and behaviour of the material is uniform throughout, meaning that it is not able to adapt to non-uniform environments. Here we create and study a metamaterial, based on the Miura-ori folding pattern, which has a varying geometry and graded stiffness through the material. Using kinematic analysis, we show how geometric parameters of the folding pattern can be varied to create both rigid foldable and self locking stages. We demonstrate both experimentally and numerically that the metamaterial can achieve periodically graded stiffness when subjected to out-of-plane compression, and the responses can be tuned by changing the underlying geometric design. We obtain a metamaterial with superior energy absorption capability compared with uniform tessellating repeat units, and anticipate that this strategy could be extended to other metamaterials to impart them with non-uniform and graded mechanical properties.