Stress Relaxation Behavior of Knitted Fabrics under Uniaxial and Strip Biaxial Excitation as Estimated by Corresponding Principle between Elastic and Visco-Elastic Bodies

Abstract

The stress relaxation behavior of four kinds of knitted fabric under a constant strip biaxial strain applied instantly was estimated in the rectangular coordinate system rotated by arbitrary angle τ from the coordinate system along the structural principal axis direction. The stress relaxation curves for the four kinds of fabric indicated the existence of rapid and slow relaxation mechanisms. To analyze the application limit of the corresponding principle to an anisotropic body with the visco-elastic behavior, a four-element model with two springs and two dashpots was adopted as a convenient tool. The stress relaxation curves measured experimentally were confirmed to follow the visco-elastic behavior by the four-element model. The predicted curves calculated by the corresponding principle were compared with the experimental curves, when the experiments were performed for a rectangular coordinate system rotated by arbitrary angle τ from the coordinate system along the structural principal axis direction under strip biaxial extension. The comparison provided good agreement for the fabrics. Furthermore, as the different excitation mode, the stress relaxation behavior was measured for a uniaxial deformation mode with the dimension free in the direction perpendicular to an external applied strain. The predicted curves calculated by the corresponding principle were in fairly good agreement with the experimental curves. Thus it turned out that the corresponding principle can be approximately applied to anisotropic visco-elastic bodies such as fabrics.

Hysteresis of Tensile load — Strain Route of Knitted Fabrics under Extension and Recovery Processes Estimated by Strain History

“…It is seen that the logarithmic curve of tensile load against time can be represented as the summation of two straight lines. Of course, the applied instantaneous strain must be limited to the regions assuring the linear relationship of the logarithmic plots of tensile load (stress) versus logarithmic values of strain, as discussed in terms of the application limit of the "linearizing method" in [1,2]. The similar tendency obtained for Specimen A was confirmed for the other fabrics (Specimens B and C).…”

“…Three kinds of knitted fabric were used as test specimens and their properties are listed in Table 1 [1][2]. Each fabric was cut into strips of 10 × 10 cm 2 .…”

“…In [1][2][3], we studied the mechanical anisotropy and the non-linearity of the several knitted fabrics to study the origin of the fit of the fabrics to the human body. The analysis was carried out in terms of three categories.…”

“…One was large deformation modes [1] under strip biaxial extension (corresponding to uniaxial extension, with the fixed dimension in the direction perpendicular to stretching) using the "linearizing method" proposed by Kawataba et al [4,5]. 1 The second was the stress relaxation mechanism [2] using plain Abstract Hysteresis phenomenon of tensile load (stress) under extension and recovery processes were estimated in terms of time dependence of tensile load by using several kinds of knitted fabrics. The measurements were done under strip biaxial extension corresponding to uniaxial extension with a fixed dimension in the direction perpendicular to elongation.…”

“…Certainly, the analysis of hysteresis under extension and recovery routes is a difficult problem and there is no fundamental concept in any material science fields. This paper deals with the tensile load and strain relationship under extension and recovery processes to analyze considerable hysteresis of knitted fabrics according to our previous studies [1][2][3]. To pursue the analysis, the hysteresis is simply analyzed as a hypothesis associated with stress relaxation and the estimation is carried out by using hereditary integrals.…”