Study on negative Poisson’s ratio of auxetic yarn under tension: Part 2 – Experimental verification

Abstract

Auxetic yarn was successfully produced by a wrap filament and a core filament based on a ring-spinning system, which showed an auxetic effect when stretched, that is, expanding transversely under tension. Yarns were spun by different structural parameters of the core filament and the wrap filament, including diameter ratio, helical angle and tensile modulus of the wrap filament. Corresponding tensile tests were utilized to analyze the effects of structural parameters and performance on outer contour deformation of auxetic yarn. Experimental results showed that the outer contour of auxetic yarn expanded transversely under tension and there existed significant negative Poisson's ratio values in the Poisson's ratio-strain curve, and it was found that the auxetic effect became more observable with a higher diameter ratio of the core filament to the wrap filament, and lower helical angle and larger tensile modulus of the wrap filament. Moreover, compared with theoretical results by theoretical modeling in Part I, good relations of Poisson's ratio-strain curves were obtained between experimental and theoretical results. This proves the effectiveness of spinning auxetic yarn by selecting reasonable components of yarn and it is feasible to design yarn with a negative Poisson's ratio effect.