Fatigue in Textile Fibers

Abstract

Experimentation has meluded investigation of the effects of frequency on the hfetime distributions of an acrylic sample and Types 52 and 420 Dacron2 fibers. Increase of frequency of cyclic loading was found to result In an increase in the dispersion of life times (in number of cycles) in the acryhe sample. The effect of mereasing the frequency was to raise the general level of the lifetime distributions of both Types 52 and 420 Dac ron. In general, the scatter in lifetimes at any one frequency was found to be much smaller for these samples than it was for the acrylic. The distributions for the two Dacrons were observed to be virtually unimodal. The third asymptotic function was acordmgly assumed to be apphcable. Estimates of parameters of this distribution. at various frequencies, were caculated and tabulated. A noteworthy finding was that while Type 420 Dacron has higher average lifetimes at various frequencies than Type 52, the minimum lifetimes of both are effectively zero. The average number of cycles to failure was found to increase with frequency in all three samples, although not in expected accord with a simple linear relationship. A possible explanation for the deviations is offered. Auxiliary tests, made in an attempt to account for the large differences in fatigue behavior between Type 52 and 420 Dacron, showed the latter to have substantially higher molecular weight and better orientation.