Development of auxetic warp knitted fabrics based on reentrant geometry

Abstract

This paper reports a novel method to fabricate auxetic warp knitted fabrics on a tricot warp knitting machine based on a special structure design and knitting process. Three auxetic warp knitted structures were successfully developed and all of them were designed to form a reentrant hexagonal geometry to acquire an auxetic effect. To provide the fabrics with reentrant frames, elastomeric yarns and stiff yarns were used to form the elastic underlaps and stiff underlaps, respectively. While the elastic underlaps can keep the reentrant structures stable, the stiff underlaps can support the reentrant structures to keep their reentrant frames. To alleviate the transfer of yarns in the loops under tension, an additional front yarn guide bar was used to feed binding yarns to basic reentrant structures. After knitting, all the fabrics were subjected to a heat setting process to keep their shape and a tensile test to assess their auxetic behavior. The experimental results showed that all the fabrics exhibited an obvious auxetic behavior within a wide range of strain. In particular, the fabrics retained auxetic behavior until breaking when stretched in the wale direction, and the Poisson’s ratio of the fabrics could be as low as –0.5. On the other hand, the fabrics exhibited a large tensile elongation when stretched in the course direction and their Poisson’s ratios changed from negative to positive after the tensile strain exceeded a certain value.

Design of warp knitting electronic shogging system based on mixed-velocity planning curve

“…Deriving v p (t), the acceleration curve formula a p (t) is shown in equation (20): According to the movement characteristics of guide bar lapping, h p ð0Þ ¼ 0, h p ðt f Þ ¼ h, v p ð0Þ ¼ 0, v p ðt f Þ ¼ 0, a p ð0Þ ¼ 0, a p ðt f Þ ¼ 0, these parameters are substituted to equation (16), equation (18), and equation ( 20) respectively. The constants…”

“…f can be obtained. 16) and equation (18), the formulas of position trajectory h p (t) and velocity curve v p (t) for quintic polynomial can be calculated as follows:…”

“…The fabric structure or the pattern effect are decided by the law of guide-bar shogging motion, 18 and the knitting speed is decided by dynamic response performance and the positioning accuracy of the guide-bar transverse motion. To improve the dynamic response performance and the positioning accuracy as well as achieving a better knitted effect, in the present study an electronic shogging system for the warp knitting machine via the mixed-velocity planning curve is designed.…”

Finite Element Modeling of Auxetic Warp‐Knitted Fabric Made of Re‐entrant Geometry

“…[ 4 ] This unusual behavior has also motivated various researchers to develop different types of auxetic fabrics. [ 2,5 ] To date, auxetic fabrics which have been developed can be roughly divided into auxetic woven fabrics, [ 6–12 ] auxetic‐knitted fabrics, [ 1,13–18 ] auxetic nonwoven fabrics, [ 19–21 ] and special auxetic fabric structures. [ 22 ]…”

Numerical Analysis of Binding Yarn Float Length for 3D Auxetic Structures

“…Tensile tests were conducted after heat setting and it was concluded that the fabrics show auxetic behavior in a wide strain range. [ 16 ] Hu et al developed three types of knitted auxetic structures, i.e., foldable, rotating rectangle, and re‐entrant hexagon using computerized flat knitting technology. The results showed that Poisson's ratio effect varies with strain rate.…”