Development of auxetic fabrics using flat knitting technology

Flat knitting is a widely used fabric manufacturing technology. Compared with warp knitting and circular knitting, flat knitting is characterized by its higher process flexibility and greater fabric structure variety. In this work, flat knitting technology was exploited to fabricate auxetic fabrics which laterally expand when stretched. Three kinds of geometrical structures, i.e. foldable structure, rotating rectangle and reentrant hexagon, were employed as basic reference structures for the development of these kinds of auxetic fabrics. The weft knitting processes based on these structures were specially developed and auxetic fabrics were fabricated using the computerized flat knitting machines. The Poisson’s ratio-strain curves of the developed fabrics were plotted and compared with those calculated using existing models to demonstrate the variation trends of Poisson’s ratio with the axial strain. The results reveal that except the folded fabric formed with the face loops and reverse loops in a rectangular arrangement, of which the auxetic effect firstly increases and then decreases with the axial strain, the auxetic effects of all other fabrics decrease with an increase of the axial strain. The work also shows that auxetic fabrics can be realized based on knitted structures and that flat knitting technology can provide a simple, but highly effective way of fabricating auxetic fabrics from conventional yarns.