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Fatigue in Textile Fibers

Supplementing earlier studies, experiments have been conducted on polyester (PET), aromatic polyamide (APA), and polypropylene (PP) fiber samples at various strokes and at temperatures ranging from 23° to 90°C. In the PET, at a reduced stroke of 3.4%, a rise in logarithmic lifetime with increasing temperature was found; the same trend was exhibited by this material at higher strokes. In the APA and PP, at the strokes used, declines in lifetime with increasing temperature were observed. In all cases, the general level of lifetimes was raised with reductions in stroke. Considerable growth in the PP fibers during fatiguing was observed. Review of lifetime data on PET, nylon 66, and APA samples, at a number of strokes and temperatures, leads to the con clusion that the distributions of these data tend to conform to the Weibull third asymptotic pattern. Analysis of data on lifetime as a function of stroke, for six man- made fiber samples, reveals good agreement with an expression, originally proposed for metals, which relates these two variables. It is shown that results on an acrylic and two PET samples conform to an empirical formula which relates the frequency of cyclic loading to lifetime, and, furthermore, that this formula is a simplification of a theoretical expression developed in fatigue studies at TRI.