Abstract
The fatigue lifetime of an acrylic sample was found to be expressible by the equation: L = a v ", where v is frequency, a is a function of stroke, and n is 0.72. The parameter a was found to decrease with an increase in stroke. The results are interpretable in terms of an elementary, molecular fatigue process. It is postulated that fatigue rupture occurs when a critical level of extension is reached.
A study of the residual mechanical properties of a viscose sample fatigued at various lengths was inconclusive with respect to whether fatigue failure results from the aggravation of weak spots or from over-all deterioration of the fiber substance.
Fatiguing the acrylic sample at different frequencies and for various periods of time was found to produce only insignificant differences in residual rupture properties among the fatigued fibers. The properties of these as a group, however, were found to be appreciably different from those of unfatigued fibers.
Microscopic examination of viscose fibers broken as a result of fatiguing showed the rupture surfaces to be essentially transverse planes, with no indication of fibrillation. X-ray diffraction data on fatigued nylon fibers revealed an axial lengthening of crystal lites of the material.
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