Cyclic viscoplasticity of thermoplastic elastomers

Observations are reported on a thermoplastic elastomer (ethylene-octene copolymer) in uniaxial cyclic tensile tests with a strain-controlled program and maximum elongation ratios up to λ_max = 2.0. A constitutive model is derived for the viscoplastic behavior of a polymer network with constrained chains at three-dimensional deformations with finite strains. The stress-strain relations involve five adjustable parameters that are found by fitting the experimental data. Good agreement is demonstrated between the observations and the results of numerical simulation. It is shown that the model correctly predicts the mechanical response, and its parameters are affected by amplitude of cyclic deformation in a physically plausible way.