A nonlinear fractional viscoelastic material model for polymers

In this contribution a test scheme based on tensile tests at different velocities, relaxation experiments and deformation controlled loading and unloading processes with intermediate relaxations has been used to experimentally characterize the nonlinear, inelastic material behavior. Based on the experimental observations a small strain nonlinear fractional viscoelastic material model is derived. In order to use the model within a finite element analysis, the constitutive equations have been generalized for the multiaxial case. The experimental test scheme and the fractional viscoelastic material model are subsequently applied to characterize and compute the mechanical behavior of the thermoplastic Polypropylene. After the identification of the material parameters several uniaxial and multiaxial simulations have been carried out and compared with experimental results.

► The material behavior of Polypropylene has been classified and modeled. ► Less parameter are used due to constitutive relations of fractional order. ► A process dependent viscosity function accounts for nonlinear viscoelastic behavior. ► The material parameters have been systematically identified from experimental data. ► Uni- and multiaxial simulations show the applicability of the formulated model.