Development of Auxetic Braided Yarns and Study the Effects of Braid Angle and Material Modulus on the Negative Poisson’s Ratio

Abstract

This paper introduces the braided helically wrapped yarns with negative Poisson’s ratio (NPR) exhibiting a stable structure and good practicability to avoid slippage of wrapped component from the core. The geometry and auxetic behavior of the braided helical structure for two different combinations of core materials with similar combination of wrap materials and different braiding angles have been analyzed. Two elastomeric materials i.e. Polyurethane (PU) and Polyester, were used as monofilament cores whereas two stiffer multifilament wrap yarns employed were, ultra-high molecular weight polyethylene (UHMWPE) and polyethylene terephthalate (PET). Multiple braided yarns were investigated to analyze materials’ behavior towards NPR. It was observed that the NPR strongly depended on the inherent properties of the core and wrap materials in addition to the braiding angle. The NPR value was higher for a core with relatively higher elasticity (e.g., PU elastomer compared with polyester). It was also noticed that a lower wrap angle and lower braiding speed exhibited higher NPR. The maximum NPR value using PU core wrapped at a low angle of 9° was-1.70, when tested at a low strain rate of 0.5%.