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Keywords:

  • double cord;
  • semi-auxetic yarn;
  • stitched-through

A variant of the auxetic helical yarn is explored herein by means of sewing an inextensible thin cord through an elastic fat cord, in a triangular pattern, to form a semi-auxetic yarn. When stretched in the longitudinal direction, the semi-auxetic yarn exhibits conventional and auxetic behavior in the plane perpendicular and parallel, respectively, to the plane which the inextensible thin cord lies on. A simplified model is developed herein to describe the effective Poisson's ratio of the yarn in the conventional and auxetic planes in terms of the initial half angle of the thin cord and the Poisson's ratio of the fat cord. Results show that the Poisson's ratio of the yarn in the auxetic plane decreases and increases with the initial half angle of the thin cord and the Poisson's ratio of the fat cord, respectively, while the Poisson's ratio of the yarn in the conventional plane increases with both parameters. In addition, the dominant parameters for the yarn in the auxetic and conventional planes are the initial half angle of the thin cord and the Poisson's ratio of the fat cord, respectively. Finally, other types of semi-auxetic yarns in the same category are proposed with suggested ways of producing them.