Abstract
Tensile tests made on acrylic fibers broken in fatigue revealed substantial differences in the force-extension behavior of fatigued and unfatigued samples. The average break ing tenacity of the fatigued samples was found to be higher than that of the unfatigued, while the breaking extension was substantially reduced. Segments of fibers that had been broken in fatigue, on being fatigued a second time, were found to have a mean lifetime not significantly different from the first mean lifetime. Subjecting the acrylic fibers to cyclic tension under mild conditions ("pre-cycling") was found to have no observable influence on lifetime in a subsequent fatigue test. Measurements of the break ing tenacity of fibers made immediately after a cyclic loading treatment and others made 18 hr after the treatment indicated that the "rest" period had no detectable effect on this property. The results reported in this article, on the whole, are taken as indicating that fatigue in fibrous polymers is not a process of over-all, progressive damage, but one of catastrophic nature.
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