This paper investigates the impacts of weave structures and weft density on the Poisson's ratio of worsted fabric under uniaxial extension. In this study nine groups of worsted fabrics comprising of three weave structures (twill 2/2, twill 3/1 and hopsack 2/2), each produced in three different weft densities were examined. Samples were extended in weft direction uniaxially and the Poisson's ratio of fabric in various extensions was measured. Analysis showed that the effect of both weft density and weave structure are significant with no combination effect on the Poisson's ratio. It was found that there is an exponential correlation between warp and weft crimp during fabric extension. For the worsted fabrics used in this research in all three fabric structures, fabrics with higher weft yarn density have higher value of Poisson's ratio. It was also concluded that for the fabrics with the same condition but only different in structures, this ratio is related to the structural firmness of fabric. In all three fabric structures the value of the Poisson's ratio were following the same pattern of twill 2/2, twill 3/1 and hopsack 2/2 from highest to lowest value. It was revealed that there is a high linear correlation between the crimp interchange ratio and Poisson's ratio.

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Polyester is one of the important fibers among man-made fibers. One of the finishing processes for improving the performance of polyester fabrics is weight reduction treatment. This treatment has a considerable effect on the mechanical properties of such fabrics. In this research, the effect of weight reduction treatment on changes in the Poisson's ratio of a microfiber polyester woven fabric treated with four different sodium hydroxide concentrations was studied. Poisson's ratio of the fabric at 10 levels of extension was measured. Results show that from 1% to about 5%, the Poisson's ratio increases non-linearly. After this point up to 10%, the Poisson ratio decreases by a linear trend. There is a significant variation in the results at lower extensions, and by increase in extension, this variation reduces. Statistical analysis showed that weight reduction at percentages lower than 25% does not affect the Poisson's ratio of the fabric. In the range of 6-10%, there is a high non-linear correlation between the weft crimp and Poisson's ratio. In addition, there is a high non-linear correlation between Poisson's ratio and fabric cover factor.