Measurement of yarn bending and torsion rigidities of naturally curved yarns Part 1: Monofilament yarn in helical shape

Abstract

A new method to determine yarn bending and torsional rigidities was proposed in this paper. Measuring methods of yarn bending and yarn torsion were reviewed. The proposed method is a combination of theoretical modeling, instrumentation and statistical analysis. One major feature of this method is that bending and torsional rigidities of a naturally curved yarn, like those yarns in knitted fabrics, can be measured. With the aid of modeling, a recently developed Crimped Yarn Length Measurement Instrument (CLI) is able to measure both bending and torsional rigidities at the same time. The CLI generates a large amount of data points for the force and extension relationship during the decrimping of the curved yarn, multiple regression analysis was applied to determine bending and torsional rigidities. In this way, the experimental errors can be minimized and hence more representative results can be obtained. Experimental results from the new proposed method were compared with those measured by the KES-F bending tester and the KES-YN yarn torsion tester; good agreement was evident in testing results from both methods. The advantages of the proposed method were discussed including the capability of measuring the yarn bending rigidity at higher curvature. This is part 1 of the paper in which crimped nylon monofilament was used for the study. The measurements of bending and torsion moduli of crimped short staple spun yarn unraveled from knitted fabric will be further studied in Part 2.