Auxetic behavior and other negative thermomechanical properties from rotating rigid units

Abstract

Auxetics display the anomalous property of expanding laterally when uniaxially stretched, that is, a negative Poisson鈥檚 ratio, a property that arises from 1) the presence of specific geometric features within the nano/macrostructure of the material and 2) amenable deformations in response to the applied stimulus. Herein, how ancient symmetrical esthetic artifacts have been transformed to functional auxetics through mechanisms that have ripened the field of 鈥渕echanical metamaterials鈥� and 鈥渁rchitected materials鈥� in the last decades is explored. In particular, the important role and various implementations, both in 2D and 3D, of 鈥渞otating rigid units,鈥� which range from 鈥渞otating squares鈥� to much more complex renditions at various scales of structure, are looked at. The role of rotating rigid units to generate negative thermal expansion and negative compressibility is also delved into.