Relationship Between Fatigue Behavior and Nonlinear Dynamic Viscoelasticity for High-Density Polyethylenes with Different Aggregation States
Abstract Relationships between fatigue behavior and nonlinear dynamic viscoelastic properties for the annealed, isothermally crystallized, and oriented high-density polyethylenes (HDPEs) with different molecular aggregation states were intensively discussed. Nonlinear dynamic viscoelasticity under cyclic fatigue was estimated on the basis of nonlinear viscoelastic parameter (NVP) which was defined as the contribution of higher harmonics of Fourier expanded stress signal. Fatigue strength of specimens decreased with an increase in the magnitude of NVP. Thus, NVP can be used as an index of fatigue strength for polymeric solids. Also, higher-order structural changes of specimens by cyclic straining were investigated and it was concluded that the nonlinear dynamic viscoelasticity under cyclic fatigue became dominant with an increase in cyclic straining concentration at the amorphous and/or spherulite or crystallite boundary regions.