Effects of main chain rigidity on nonlinear dynamic viscoelasticity and fatigue performance for polymeric fibres

Fatigue performance of polymeric fibres with different molecular chain rigidity was investigated based on zone nonlinear dynamic viscoelastic analyses under tension-type cyclic straining. Poly(vinyl alcohol), Nylon 6(poly(epsilon-caprolactam)), poly(ethylene terephthalate), poly(p-phenylene terephtalamide) and Vectran (a copolyester of p-hydroxy benzoate (HBA) and 2-hydroxy-6-naphthoic acid (HNA)) fibres were used as specimens. Nonlinear dynamic viscoelasticity and fatigue performance of polymeric fibres strongly depended on the chain rigidity. The polymeric fibres with rigid molecular chains showed pronounced nonlinear viscoelastic characteristics compared with those with flexible ones. Also, based on the zone nonlinear dynamic viscoelastic analyses, it was found that the nonlinear viscoelastic behaviours of polymeric fibres was predominantly induced in the recovery process rather than in the tensile process during a single period of cyclic deformation, and the more remarkable nonlinear viscoelastic behaviour was exhibited in the zone with higher strain rate. The polymeric fibre which exhibited remarkable nonlinear dynamic viscoelasticity showed extremely poor fatigue performance. (C) 1998 Elsevier Science Ltd. All rights reserved.