Intensification of auxetic effect in high stiffness auxetic yarns with potential application as the reinforcing element of composite

Helical auxetic yarn (HAY) is a newly developed composite yarn with negative Poisson's ratio. HAYs offers advantageous merits as a reinforcing element in composite materials. In this paper high stiffness HAYs composed of Nylon filament core and fine steel wire wrap yarns were developed. The importance of the stiffness ratio of the wrap to the core components in the resultant auxetic yarn was examined. The differences between instantaneous and engineering Poisson's ratio analyses in the understanding of the strain-dependent behavior of HAY was investigated. Results revealed that the utilization of the fine steel multifilament in the developed HAY samples enormously improves the stiffness of HAY. It was possible to obtain an elastic modulus of 9 GPa and a maximum auxetic effect of -16.82 in the samples. It was concluded that such highly stiff auxetic yarn can successfully be used as reinforcement in various composite materials such as cementitious composites.