The Miura Ori Geometry: from brilliant theory to surprising auxetic properties

In the last few years, “Metamaterials” have become very popular in materials’ mechanics. The most interesting aspect of such structures is that their mechanical response is strongly linked to the geometrical configuration rather than their chemical composition. The Miura Ori is a particular origami technique that consists of folding a sheet to realize a lattice of periodic cells: the leading parameters of the cells are the folding angles and the length of the edges. The literature demonstrates that a careful selection of these parameters consents to achieving an auxetic response of the structure, i.e., the global Poisson Coefficient is negative. In this work, the authors want to investigate the Miura Ori auxetic behavior experimentally. Because sharp edges characterize the Miura Ori cell, the authors opted to produce the specimens with a FFF 3D printing technology and analyze the displacement field with Digital Image Correlation. The results show a strong correlation between the Poisson ratio and specimen thickness, thus allowing for significant negative values. In addition, DIC results are in good agreement with numerical simulations.