Stress relaxation behavior of knitted fabrics under uniaxial and strip biaxial excitation as estimated by corresponding principle between elastic and visco-elastic bodies

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 0 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 0 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.