Inelastic material behavior of polymers – Experimental characterization, formulation and implementation of a material model

In this contribution an experimental procedure based on displacement controlled tensile tests at different rates of loading, relaxation experiments and deformation controlled loading and unloading processes with intermediate relaxations to experimentally characterize and classify the nonlinear, inelastic mechanical behavior of polymers is presented. These experiments provide data for a structured approach to parameter identification. In line with the experiments, a small strain uniaxial viscoplastic material model is derived, subsequently generalized to multiaxial loadings and implemented into a finite element program. The combination of the experimental procedure and the proposed material model is then used to characterize and model the mechanical behavior of the thermoplastic polypropylene. After the identification of the necessary material parameters, stress–strain curves have been computed for different uni- and multiaxial loadings and are compared with experimental results.

► Experiments, a viscoplastic material model and numerics are jointly discussed.
► Stress update algorithm and related algorithmic tangent stiffness are given.
► A structured approach to parameter identification is applied.
► Very good agreement between experiments and model predictions is obtained.
► Modular structure of the material model allows for application to other polymers.