AbstractDepending upon the fiber material, some of the experimental variables can have a profound effect on the dynamic tensile modulus vs. temperature data. With the use of an experimental fiber (25°C220°C; hot stretched), the effect of several variables, e.g., moisture/volatiles, annealing/relaxation, frequency (strain rate), pretension, and strain on the modulus retention term (E100°C/E25°C) × 100 have been studied. Of these variables, pretension and especially strain dramatically increase the modulus retention and this effect is attributed to the elastic orientation under force (EOF), i.e., it exists only in the presence of tensile forces and is reversible. Such an effect was insignificant for Kevlar (Tg− 375°C) and absent for steel wire. Dynamic modulus measurements at 25°C using sonic techniques also support the EOF phenomenon in polyethylene yarns (Tg∼ −30°C) but not in Kevlar polymide yar
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