Effect of unit-cell geometry and dimensions on the Poisson’s ratio of purl-based auxetic weft-knitted fabrics

Auxetic weft-knitted fabrics offer distinctive deformation characteristics that can be tailored through structural geometry. This study investigates the influence of unit-cell geometry and dimensions on the Poisson’s ratio of purl-based weft-knitted auxetic fabrics. Three geometries, namely square, rectangular, and square–rectangular, were produced with three unit-cell dimensions of 6 × 6, 8 × 8, and 10 × 10 stitches using a computerized flat knitting machine. Poisson’s ratio was experimentally evaluated in both the course and wale directions over a tensile strain range of up to 100%. The results showed that auxetic behavior was strongly dependent on fabric geometry and loading direction. Square-patterned fabrics exhibited persistent auxetic behavior in the course direction but positive Poisson’s ratios in the wale direction. Rectangular-patterned fabrics showed auxetic behavior only in the wale direction and over a limited strain range. The square–rectangular geometry exhibited auxetic behavior in both directions, with its wale-direction response being particularly dependent on unit-cell dimension. Experimentally, the 6 × 6 square–rectangular configuration lost its auxetic behavior in the wale direction after approximately 8% strain, whereas the 8 × 8 and 10 × 10 configurations maintained negative Poisson’s ratios up to 100% strain. Changes in unit-cell dimension also produced geometry- and strain-dependent variations in the magnitude and persistence of auxetic behavior rather than a uniform trend. Overall, the measured responses indicate that unit-cell geometry, dimension, and loading direction are important structural parameters for tailoring the directional and strain-dependent auxetic response of purl-based knitted fabrics.