Effect of Main-Chain Rigidity on Fatigue Behavior of Polymeric Fibers Based on Zone Nonlinear Viscoelastic Analysis

Abstract

Fatigue behavior of high-strength and high-modulus polymeric fibers was investigated based on nonlinear dynamic viscoelastic analysis under tension-tension cyclic strain condition. Poly(vinyl alcohol) (PVA) and thermotropic polyester(Vectran) fibers were used as specimens. The zone nonlinear dynamic viscoelastic analysis was proposed as a new approach to investigate the nonlinear dynamic viscoelastic behavior in different deformation stages during one period of cyclic deformation for polymeric materials. It was found that the nonlinear dynamic viscoelasticity strongly depended on the rigidity of backbone chains of polymers. The polymeric fibers with rigid polymer chains showed remarkable nonlinear viscoelastic characteristics comparing with that with fiexible polymer chains. Also, it was found from the zone nonlinear dynamic viscoelastic analyses that the nonlinear viscoelastic behavior during cyclic deformation was predominantly induced during the recovery process rather than the tensile process for polymeric fibers, and the more remarkable nonlinear viscoelastic behavior was exhibited in the zone with higher strain rate. The polymeric fibers with rigid polymer chains exhibited more remarkable nonlinear viscoelasticity and poorer fatigue strength. At the onset of fatigue failure, a sudden increase in nonlinear dynarnic viscoelasticity was observed for polymeric fibers. The sudden increase was considered to relate with the remarkable irreversible structural changes before the fatigue failure for polymeric materials.