A new method of representation of fiber creep data tensile creep behavior of some acrylic fibers

Summary Fiber creep data are usually represented as plots of extension versus time at constant stress and temperature. Fiber samples, however, exhibit some degree of variability in structure from filament to filament. Consequently, even when initial applied stresses are nominally equivalent (as determined by measurement of cross-sectional area, and load), the creep of individual fibers can differ significantly, and the creep behavior of a sample can only be characterized statistically.Structural parameters such as orientation, which affect fiber properties greatly, and therefore creep, are not considered in the conventional representation of creep data. Orientation, in turn, is associated with stretch or extension. On this basis, creep, i. e. creep rate, can be expected to depend on extension.In the proposed method for representing creep data, the rate of creep is related to the extension at a constant time and temperature. In these so-called isochronal creep rate curves, the use of stress as an independent variable is omitted, and is replaced by extension. This method of representation discloses common creep characteristics in fibers, which, though taken from the same sample, exhibit widely different creep behavior when treated conventionally. In this way, the creep behavior of the whole sample can be conveniently represented. These plots reveal more detail than the ordinary creep curves, and indicate different creep mechanisms within certain extension regions as well as the stretch-relaxation history of the particular fiber sample. In this paper, the aspects and limitations of these two methods of representation of creep data are discussed, and their relative merits are demonstrated using experimental acrylic fibers.