Towards textile metamaterials: a pathway to auxeticity and tensegrity in a needle-punched nonwoven stiff felt

Auxetics are a class of mechanical metamaterials that show a negative Poisson's ratio, which has been of interest as a mechanism to provide enhanced performance in, for example, composite materials and energy dissipation structures. Given this interest, there is a need to realize this behavior in a practical fashion. In this work, we move towards identifying and understanding such materials by examining the out-of-plane auxeticity of fiber networks contained in stiff felt nonwovens. The network contains fiber connections that provide a structure which is intermediate to a physically entangled nonwoven and a composite. The results show that these nonwovens display an out-of-plane auxetic response that is at least partially reversible. Additionally, it was found that the elastic-plastic behavior seen at larger strains can be described using concepts of multistable tensegrity structures, supporting the suggestion that tensegrity and auxeticity can coexist in some metamaterial structures.