摘要：

Relaxation properties are very important for various kinds of textiles and especially for technical ones. Technical textiles in their usage sometimes undergo stress for a long time and their behaviour after which is very important for prediction of the possibility for their further usage. For the prediction of such properties and long-lasting relaxation investigation, the relative stress relaxation P/P0, which characterizes the rate of relaxation, is used. In the present paper it was found that this rate cannot be described as a linear dependency on the logarithm of the time – in a certain time the character of the rate changes. Such a phenomenon is clearly visible for multifilament polyester yarns as well as for woven fabrics from them. The time in which the character of the rate of relaxation changes is herein proposed to be named as the break-point of the relaxation process. In our work it was found that the break-point of polyester (PET) yarns and fabrics exist after 100 seconds. It was also discovered that the rate of relaxation in the log(t) scale can be described by two straight lines and the values of relaxation in the long term can be predicted by the rate of relaxation of the second linear dependency. A method which allows to predict the relaxation process up to 200,000 seconds after testing till 500 seconds is presented. The reliability of such a prediction is lower than 2%.

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