The helical auxetic yarn – A novel structure for composites and textiles; geometry, manufacture and mechanical properties

This paper introduces a novel fibre structure known as the helical auxetic yarn (HAY). The geometry of the yarn is defined and the manufacturing process described. A range of HAYs have been manufactured that vary the geometric properties of the structure. A systematic study of the yarns has been completed to evaluate the effect on the auxetic behaviour of the geometry. We also characterise the component fibres and yarns and discuss the influence of geometric and material effects on the observed Poisson’s ratio of the yarns.It can be shown that the starting wrap angle of the yarn has the greatest effect on auxetic behaviour both in terms of magnitude and the strain range over which it may be observed.The maximum negative Poisson’s ratio observed for a yarn manufactured from conventionally available monofilaments with positive Poisson’s ratio is −2.7.