Fatigue in Textile Fibers

Abstract

Equipment on which six fiber specimens can be simultaneously fatigued in cyclic tension, at one common strain amplitude, has been developed and constructed. Fre quencies are continuously variable from zero to 18 cycles/sec, and the total stroke is adjustable from zero to 1 in. Provisions are made for the automatic taking up of the slack resulting from growth in each fiber and stopping of the machine at the conclusion of a test. The growth in each specimen and the time to rupture are recorded on a strip chart. Results on two viscose samples and one experimental acrylic sample suggest that the growth that occurs during the fatiguing has two phases, in both of which the increase in extension is substantially linear with the logarithm of time. The rate of extension (per unit log time) in the initial phase is at least twice as great as in the later phase. In a third viscose sample, of high crystallinity, in which the growth rate of extension and the extensions at break were both low, the distinction between the two phases prac tically vanishes. Fatigue lifetimes of the acrylic sample appear, from plots on probability paper of the individual lifetimes of the specimens, to conform better to a logarithmic normal distri bution than to the normal.