EFFECTS OF MAIN-CHAIN RIGIDITY ON NONLINEAR DYNAMIC VISCOELASTICITY AND FATIGUE PERFORMANCE FOR POLYMERIC FIBERS

Fatigue performance of polymeric fibres with different molecular chain rigidity was investigated based on zone nonlinear dynamic viscoelasti c analyses under tension-type cyclic straining. Poly(vinyl alcohol), N ylon 6(poly(epsilon-caprolactam)), poly(ethylene terephthalate), poly( p-phenylene terephtalamide) and Vectran (a copolyester of p-hydroxy be nzoate (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 polym eric fibres with rigid molecular chains showed pronounced nonlinear vi scoelastic characteristics compared with those with flexible ones. Als o, based on the zone nonlinear dynamic viscoelastic analyses, it was f ound that the nonlinear viscoelastic behaviours of polymeric fibres wa s predominantly induced in the recovery process rather than in the ten sile process during a single period of cyclic deformation, and the mor e remarkable nonlinear viscoelastic behaviour was exhibited in the zon e with higher strain rate. The polymeric fibre which exhibited remarka ble nonlinear dynamic viscoelasticity showed extremely poor fatigue pe rformance. (C) 1998 Elsevier Science Ltd. All rights reserved.