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.
27—Relaxation of Stress in Stretched Cellulose Fibres
An apparatus is described for making stress—relaxation tests on yarns or monofils at controlled humidity and temperature. It incorporates an optical lever for measuring the tension, and observations can be made from 1/20 second after the start of an experiment up to several weeks. Cotton, flax, viscose, and cellulose acetate yarns were rapidly stretched at 65 per cent r.h. and 25°C, and the decay of tension followed for 24 hours. Further tests were made in which the specimens were held stretched for 15 minutes and relaxed for two hours, repeatedly, until mechanically conditioned. The results are expressed graphically as stress against log (time) and are in good agreement with those of other workers, over the limited time range which they have used. The fraction of the initial stress which decays is quite large. Thus taking the stress at one second after extending as a reference value, the decay of stress from 1/10 second to a day is approximately 30 to 50 per cent for cotton, 42 to 83 per cent for viscose...
Test Method for Cloth Fell Displacement Caused by Relaxation
A test method is presented for measuring cloth fell displacement during relaxation of fabric yarn combinations on a tensile tester. The equipment consists of a CCD camera, a frame grabber, and appropriate software. The method is used to analyze the cloth fell displacement of twenty different fabrics. The influence of fabric parameters is determined using statistical techniques.