Varying the performance of helical auxetic yarns by altering component properties and geometry

Abstract

This paper presents a systematic study of the helical auxetic yarn (HAY) via careful in-house fabrication and characterisation of a wide range of polymeric fibres and yarns. It provides a better understanding of the auxetic behavior of the HAY in order to tailor their properties for specific applications. The study focused on three parameters: component moduli, the core/wrap diameter ratio and the initial wrap angle. The results show that a larger difference in component moduli, a higher core/wrap diameter ratio and a lower initial wrap angle can produce a larger maximum negative Poisson's ratio value and thereby a better auxetic performance for HAYs. All three parameters could be carefully utilised when in combination to achieve the required auxetic behaviour of HAYs. Moreover, the instantaneous true Poisson's ratio analysis accurately presents the instantaneous behaviour of highly strain dependent HAYs.

Parametric sensitivity analysis to maximise auxetic effect of polymeric fibre based helical yarn

“…6). This is possible, as the recent results by Zhang et al [27] showed that a larger difference in component moduli, a higher core/wrap diameter ratio and a lower initial wrap angle can produce a larger maximum NPR value and thereby a better auxetic performance for HAYs.…”

“…[23,[26][27]) has considerable potential to improve HAYs properties and therefore provides a means of evaluating the auxetic quality with potential applications in resisting high velocity impact.…”

Large-scale manufacturing of helical auxetic yarns using a novel semi-coextrusion process

“…18 Sample width measurements for fibers and HAYs were obtained using MATLABR2011b to analyze the acquired images. 24 The engineering Poisson's ratio for yarns was computed using measured engineering strains " y and " x…”

“…Zhang et al 23 fabricated a novel three-component auxetic structure based on a HAY and they indicated that the coating thickness was identified as a new design parameter for tailoring the auxetic effect. Zhang et al 24 carried out a systematic study of HAYs using a wide range of fibers and they investigated the auxetic performance of HAYs by comparing the instantaneous true and engineering Poisson's ratio; the results demonstrated that the instantaneous true Poisson's ratio analysis was able to accurately show the instantaneous behavior of highly strain-dependent HAYs. In a recent dynamic thermo-mechanical and impact study of HAYs, 25 an optimal initial wrap angle of 27 o has been found to give the best combination of stiffness, energy absorption and auxetic performance of HAYs.…”

Large‐scale extrusion of auxetic polypropylene fibre

“…As the HAY is stretched lengthwise, the thin wrap yarn straightens and pushes the core yarn into a helical configuration, producing an overall increase in the thickness of the composite yarn system and, therefore, auxetic response. This approach requires careful control of the wrap yarn placement on the core yarn, and it has been shown that the magnitude and presence of the auxetic effect is dependent on wrap yarn angle and the core and wrap yarn diameters and moduli . A variant on the HAY is to embed the thin stiff component within the thick compliant core .…”