Development of auxetic knitted fabrics and investigation of their structural properties

Poisson's ratio (PR) is a mechanical property representing the lateral behavior of materials under an axial load. Typical natural materials possess a positive PR, which means when they are stretched in one direction, they shrink in the direction transverse to the loading direction. The material, which shows expansion in both width and length when force is applied, has a negative poisson ratio and they are called "auxetic materials". Due to their superior properties, the materials with negative possion ratio (auxetic materials) can meet the demand for different materials, especially in technical textiles. In this study, the development of auxetic knitted fabrics and their structural properties were examined. It was aimed to produce auxetic knitted fabrics suitable for use in sportswear products on flat knitting machines. PR measurement methods in the literature were examined and new measurement method development studies were carried out. In addition to the auxetic knitted fabrics in the literature, the structures of auxetic materials other than textiles were adapted to the knitting pattern program and 33 samples were produced in different knits. The use of auxetic knitted fabrics in sportswear products was investigated by examining the relationship between PR and fabric performance properties. It was seen that, as the PR decreased, the samples expanded in the width direction and the porosity values increased, leading to an increase in permeability. With increasing elongation, auxetic materials have more air and vapor permeability than positive PR samples. The thermal conductivity also increases in auxetic materials in general. Considering these properties, it is possible to design fabric with high permeability and high heat conduction properties and thus a more comfortable fabric.