ANALYSIS OF FATIGUE BEHAVIOR OF HIGH-DENSITY POLYETHYLENE BASED ON NONLINEAR VISCOELASTIC MEASUREMENT UNDER CYCLIC FATIGUE

Fatigue behaviors of annealed and isothermally crystallized high-densi ty polyethylenes (HDPEs) were investigated on the basis of nonlinear d ynamic viscoelastic measurement during the fatigue process. Nonlinear viscoelasticity was evaluated in terms of nonlinear viscoelastic param eter (NVP) which was defined as the contribution of higher harmonics o f Fourier expanded stress signal. In the cases of the annealed and iso thermally crystallized HDPEs, the apparent dynamic storage modulus dec reased, NVP and tan delta increased with an increase in the magnitude of imposed strain amplitude. Since the fatigue strength decreased when the contribution of NVP became dominant, the magnitude of NVP can be used as a measure of fatigue characteristics of polymeric solids. Also , the origin of NVP for the annealed and isothermally crystallized HDP Es was discussed on the basis of the spherulite structure.