Inverse Stress Relaxation and Viscoelastic Recovery of Multifilament Textile Yarns in Different Test Cycles
The article presents the results of the experimental research of inverse stress relaxation (IR) and viscoelastic recovery (VR) that take place in acetate and polyester multifilament yarns in dependance on the mechanical pre-history. The above-mentioned time-effects are investigated in two different – stress relaxation (R-) and creep (C-) testing cycles. The fact that inverse stress relaxation process takes place in Ctest cycle, i.e. after previous sustaining the specimen at constant load is experimentally confirmed. It is shown that viscoelastic recovery is the slower process than the inverse stress relaxation. At identical elongations of the yarns at the end of loading period the inverse relaxation and viscoelastic recovery processes go on similarly regardless of the character of testing cycle.
Simulation of Procedures to Avoid Set Marks in Weaving Caused by Relaxation
Relaxation of warp yarns and fabric is one of the causes of set marks (starting places) in weaving. Loom manufacturers have developed experimental procedures to diminish these set marks, and this paper describes mathematical simulations of several such procedures. The simulations use a previously developed model for the viscoelastic behavior of warp yarn and cloth and for the cloth fell position. The aim of the paper is to provide a scientific background for anti-set mark procedures.
Thick and Thin Places in Fabrics during Weaving:Part 3: Development of Preventive Device against Thick and Thin Places in Fabrics
The purpose of this article is to clarify the relation between the causes for setting-on areas in fabrics and their scales. We have made several experiments to grasp the tendency of scales and analyzed them by using the equations on warp tension which were established in Part 1 and the equation on bending of the race which was introduced in this report.In the light of the results, we have tried to make clear the causes for setting-on areas and find the means to avoid them. We have reached the following conclusions:(1) To make setting-on areas small in scale, the moment of inertia of the tension roller system must be made as small as possible for the automatic bobbin changing cotton loom and the spring constant of the tension spring must be made as small as possible for the water jet loom.(2) The change of the loom speed when the loom starts or stops has great influence on the scales of setting-on areas.(3) On the automatic bobbin changing cotton loom, the scale of setting-on areas in fabrics is affected mainly by the change of the warp tension. On the water jet loom, it is affected mainly by the bending of the race.(4) To avoid setting-on areas due to fluctuations in the beating-up tension of warp just before or after the loom starts, we should do well to equalize this tension to the tension in its stationary running state. That is, compensate for the warp tension around the beat-up point so as to satisfy the following equation: where ∫ba; f(t)dt=∫ba; g(t)dt f(t): Warp tension curve in stationary running state. g(t): Warp tension curve in starting or stopping state. a, b: Beginning and end of beating-up.