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.
Inverse Stress Relaxation in Textile Yarns After the Blockage of Viscoelastic Recovery
Viscoelastic properties of acetate and polyester multifilament yarns in the compound loading cycle are theoretically and experimentally studied and the features of inverse stress relaxation (IR) after the blockage of viscoelastic recovery of the yarns are revealed in the study. Modelling method of the processes at the referred loading cycle is proposed on the basis of generalized Maxwell model. Analysing the behaviour of the model possessing different relaxation time spectra it was found that the longer is free recovery of the model until its blockage the less is the resulting recovery power of the model. The duration of recovery is more sensitive to the changes in the amount of the resulting IR in the model possessing more short relaxation times. To prove the theoretical findings the experimental investigation was provided with acetate (16.6 tex) and polyester (15.6 tex) multifilament yarns analysing their behavior in the same loading cycle. The experiments confirmed basic theoretical findings. Some differences in the reaction of acetate and polyester yarn to the blockage of their viscoelastic recovery are shown.
Influence of Strain Rate and Yarn Number on Tensile Test Results
The influence of strain rate and yarn number on tensile test results is investigated using a model to describe the tensile curve. A good correlation is obtained with the experimental stress-strain curves. The influence of the yarn number on the tensile modulus and the tensile curve is not quite the same for ring and rotor yarns.