Layered Miura-ori cellulose structures for tunable mechanics

Miura-ori is a flat-foldable origami geometry that can be industrially deformed from a continuous planar web and therefore has potential in high-volume packaging and other applications. Combining several Miura-ori layers of different scales together leads to a complex material with extended layer joints and new functional properties. We designed several experimental systems based on machine-made Miura-ori paperboard and similar hand-folded scaled geometries. The measured bending and compression properties depended strongly on the location of the contacts between the folds of the different layers. A similar stress plateau was obtained for two- and three-layer structures consisting of only one Miura geometry due to head-on contacts between the valley and mountain folds of subsequent layers. However, if the middle longitudinal geometry of the three-layer structure was scaled, the deformations in that layer could be drastically different depending on the relative phases of the outer layers. The triple scaling gave rise to synchronous post-buckling deformation driven by the overlapping mountain folds of the outer layers. This resulted in soft cushioning behavior with an extended stress–strain plateau. In contrast, the opposite outer-layer phases forced irregular post-buckling deformations in the double-scaled middle layer, which caused the stress to increase almost linearly with compression strain. The achieved family of sustainable lightweight cushions with anisotropic and tunable mechanical properties could be used to protect objects of different weights and fragility. As the underlying geometric principles are general, they could also be applicable in modifying mechanical properties and energy absorption in other metamaterials consisting of layered geometries.