Auxetic behavior from rotating triangles

Abstract

Materials with a negative Poisson’s ratio (auxetic) exhibit the very unusual property of becoming wider when stretched and narrower when compressed [1]. This property gives a material several beneficial effects such as increased shear stiffness, increased plane strain fracture toughness, increased indentation resistance and improved acoustic damping properties [1–5]. In recent years several auxetics have been manufactured by modifying the microstructure of existing materi- als, including foams [2, 6] and microporous polymers [7, 8]. A number of molecular-level auxetics have also been discovered, proposed or synthesised including nanostructured polymers [1, 9–12], metals [13], silicates [14, 15] and zeolites [12, 16, 17]. In all of these cases, one may observe that the negative Poisson’s ratio results from the very particular nano or microstructure of the material (ge- ometry) and the way this deforms when subjected to loads (the deformation mechanism).