EFFECT OF MAIN-CHAIN RIGIDITY ON FATIGUE BEHAVIOR OF POLYMERIC FIBERSBASED ON ZONE NONLINEAR VISCOELASTIC ANALYSIS

Fatigue behavior of high-strength and high-modulus polymeric fibers wa s 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 zo ne nonlinear dynamic viscoelastic analysis was proposed as a new appro ach to investigate the nonlinear dynamic viscoelastic behavior in diff erent deformation stages during one period of cyclic deformation for p olymeric materials. It was found that the nonlinear dynamic viscoelast icity strongly depended on the rigidity of backbone chains of polymers . The polymeric fibers with rigid polymer chains showed remarkable non linear viscoelastic characteristics comparing with that with flexible polymer chains. Also, it was found from the zone nonlinear dynamic vis coelastic analyses that the nonlinear viscoelastic behavior during cyc lic deformation was predominantly induced during the recovery process rather than the tensile process for polymeric fibers, and the more rem arkable nonlinear viscoelastic behavior was exhibited in the zone with higher strain rate. The polymeric fibers with rigid polymer chains ex hibited more remarkable nonlinear viscoelasticity and poorer fatigue s trength. At the onset of fatigue failure, a sudden increase in nonline ar dynamic viscoelasticity was observed for polymeric fibers. The sudd en increase was considered to relate with the remarkable irreversible structural changes before the fatigue failure for polymeric materials.