Auxetic fabric structures and related fabrication methods

A method of using a warp knitting technique to fabricate an auxetic warp knitted fabric having a net structure, said method comprising:

• fully setting at least one guide bar of a plurality of guide bars of a warp knitting apparatus;
• partially setting at least one guide bar of the plurality of guide bars;
• forming a first chain of connected diagonal ribs, the first chain extending along a course direction, wherein adjacent diagonal ribs of the first chain extend along different diagonal directions and are connected at a valley or a peak of the first chain, and wherein each of the diagonal ribs of the first chain forms an angle α relative to the course direction;
• a second chain of connected diagonal ribs, the second chain extending along the course direction, wherein adjacent diagonal ribs of the second chain extend along different diagonal directions and are connected at a valley or a peak of the second chain, and wherein each of the diagonal ribs of the second chain forms the angle α relative to the course direction;
• and
• vertical ribs extending along a wale direction perpendicular to the course direction, wherein the diagonal ribs of the first and second chains and the vertical ribs each comprises warp knit stitches comprising loops from one or more yarns, wherein the loops are intermeshed and the intermeshed loops extend along a course direction or a wale direction, wherein each vertical rib connects a peak of the first chain to a valley of the second chain, and wherein at least some of the valleys of the first chain and some of the peaks of the second chain are unconnected and separated by gaps along the wale direction;
• wherein in a relaxed state, the angle α is a non-zero angle, and the fabric comprises a width along the course direction and a length along the wale direction;
• wherein when the fabric is stretched along either the course direction or the wale direction, the diagonal ribs of the first and second chains move towards aligning with the course direction and the angle α decreases from nonzero towards zero so that each chain becomes longer along the course direction and the width of the fabric increases, and the gaps between the unconnected valleys of the first chain and peaks of the second chain expand along the wale direction so that the length of the fabric increases in response to the stretch;
• and
• wherein the fabric has a Poisson's ratio with a value that is less than or equal to 0.