Helical Yarn Research Articles

Flexible helical yarn swimmers

We investigate the motion of a flexible Stokesian flagellar swimmer realised as a yarn made of two intertwined elastomer fibres, one active, that can reversibly change its length in response to a local excitation causing transition to the nematic state or swelling, and the other one, a passive isotropic elastomer with identical mechanical properties. A propagating chemical wave may provide an excitation mechanism ensuring a constant length of the excited region. Generally, the swimmer moves along a helical trajectory, and the propagation and rotation velocity are very sensitive to the ratio of the excited region to the pitch of the yarn, as well as to the size of a carried load. External excitation by a moving actuating beam is less effective, unless the direction of the beam is adjusted to rotation of the swimmer.

The determination of the twist level of the Chenille yarn using novel image processing methods: Extraction of axial grey-level characteristic and multi-step gradient based thresholding

This paper presents, a new and fast image analysis based method, namely extraction of axial grey-level characteristic (EAGLC), for directly determining the dimensions of a local structural texture, as observed on the axis of the Chenille yarn. The EAGLC signal, obtained from the texture composed by the helically wrapped core yarns, allows identifying the twist level and its variations. Additionally, a novel indirect method, namely multi-step gradient based thresholding (MSGBT), including parametric equation of the elliptical cross-section helical yarn is developed to obtain the twist level using algorithmic thresholding process. Hough Transform method (HT) allows to verify the twist and twist orientation values obtained by the MSGBT method. Consequently, the EAGLC method can be used for the weak local texture compared with grey-level projection method used for strong periodic patterns as are the case in warp and weft yarns in fabric. A yarn inspection system, including optoelectronic sensor, is developed in conjunction with computer vision unit to assess the signal changes corresponding to the image regions where the twist level is determined.

Semi-auxetic yarns

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.

New Directions in Braiding

It is the intent of this manuscript to provide a general treatment of braiding: past, present, and future. A history and evolution of braiding, braiding machinery, and related engineering developments is provided with emphasis on the design, manufacture, and analysis of braided fabrics and composites. Some recent developments are briefly described, including: 1. a composite braider with axial yarns which interlace with the helicals, and in which the helical yarns do not interlace with each other – a machine now under commercial development, 2. a new braided structure, called the true triaxial braid, produced by the new machine or by proper carrier loading on a conventional Maypole braider; and 3. a computer controlled take-up system using image analysis to monitor and control braid formation. Original work ongoing at Auburn University is described and involves Jacquard lace braids with open structures for use in composites, computer aided design (CAD), computer aided manufacturing (CAM), and analysis of ordinary and lace braids for composite applications. This paper is an expanded version of an invited presentation under the title “New Directions in Braiding” at a Fiber Society presentation in Bursa, Turkey, in the spring of 2010 [1].

PREPARATION OF PVP HELICAL FIBER BY ELECTROSPINNING WITH SINGLE COLLECTION UPRIGHT COPPER NEEDLE

A convenient method was developed to fabricated helical nano-fiber yarn in one step and with high efficiency.Poly(vinyl pyrrolidone)(PVP) sol(M_w =1.3×10~6,10% in ethanol) was electrospun at the voltage of 25 kV,using a thin upright copper needle as a collector with the rotation speed of 0～1200 r/min.In this setup,centimeters-long precursor fibers are spontaneously electrospun on the tip of the upright needle target parallel to the electric field.The electrospinning process is mainly controlled by the electrostatic forces.Thus,when a grounded needle is close to the splaying jet,the splaying jet will be converged and then deposed on the needle.The yarn was formed between the needle and the spinneret,and the jet will be folded and aligned to form a self-bundling yarn.The morphologies of helical fiber were observed by scanning electron microscopy(SEM).The morphologies of PVP fibers were changed from non-helical,dispersed-helical to tight-helical fibers forming a multi-filament yarn in the various rotating speeds.The Coulomb attracting force(in the vertical direction due to the static fields between the jet and the copper thread),the Coulomb excluding force between the spinning fibers(in the horizontal direction) and the shear force (in the tangential direction due to the high rotation speed by copper needle) are the three main factors to form the helical fibers.The main advantages of producing PVP fiber yarns by this technique are the minimum polymer degradation and forming the multi-filament yarns having a high tenacity.