Fatigue in Textile Fibers

Abstract

Samples of polyester and nylon 66 fibers have been fatigued by cyclic longitudinal tension, each sample at two strokes, at various temperatures from 21° to 90°C. In the polyester, it was found that, in general, at both 4.5 and 5.9% stroke, average logarithmic lifetimes increase with temperature. Straight lines, fitted to the experimental points by the method of least squares and representing logarithmic lifetime as a function of reciprocal temperature, were observed to have negative slopes, the slope at the 5.9% stroke having the larger (absolute) negative value. In the nylon, it was found that, with a 7.2% stroke, logarithmic lifetimes tend to decrease with increasing temperatures, i.e., the slope of the least-squares line for logarithmic lifetime vs 1/T has a positive value. At a higher stroke (8.1%), for the nylon fibers, the converse is true. Thus —generalizing—in both samples the slope of the curve for logarithmic lifetime vs 1/T decreases with increasing stroke. Correspondingly, energies for the fatigue rupture process, calculated according to the Prevorsek-Lyons theory, were found to be negative for both tests on the polyester and for one on the nylon sample, with the 8.1% stroke. A small positive energy was calculated for the nylon at the 7.2% stroke. These results were, confirmed by the energies calculated from terminal growth rates measured on the polyester at the 5.9% stroke and on the nylon sample at the 7.2% stroke. It is concluded that the energy involved in fatigue rupture is identical with that related to growth during cyclic loading.