Mechanics of Elastic Performance of Textile Materials

Abstract

Theoretical analyses of the torsional recovery of filaments and singles yarns and the ply back-twist required to give balanced plied yarns are presented. The methodology employed parallels that previously reported for filament bending recovery [4]. The filaments are assumed to be linearly elastic for shear stresses below the yield stress, to have a sharply defined yield point, and to exhibit linear work-hardening beyond the yield. Time effects, although not explicitly included, are discussed. The torsional behavior of small-diameter metal wire and some polymeric filaments is, approximated by these assumptions. The effects of bending stresses and tensile stresses imposed on fibers during spinning or throwing are neglected. The yarn torque which develops from the application of a tensile stress to a twisted singles yarn, which would otherwise not exhibit any residual torque, is also neglected. However, the magnitudes of the possible effects of tension on filament torque, and filament bending on yarn torque are noted. The analytical expressions obtained for the twist recovery of filaments as a function of filament diameter, material properties, and initial twist are verified experimentally. The analytical expressions for the twist recovery of singles yarns and the ply back- twist required to give balanced plied yarns are experimentally investigated. The causes of differences between the theoretical and experimental results are discussed.