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

Fatigue behaviors of annealed and isothermally crystallized high-density polyethylenes (HDPEs) were investigated on the basis of nonlinear dynamic viscoelastic measurement during the fatigue process. Nonlinear viscoelasticity was evaluated in terms of nonlinear viscoelastic parameter (NVP) which was defined as the contribution of higher harmonics of Fourier expanded stress signal. In the cases of the annealed and isothermally crystallized HDPEs, the apparent dynamic storage modulus decreased, 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 HDPEs was discussed on the basis of the spherulite structure.