On the nonlinear response of polymers to periodical sudden loading and unloading

In practice, it happens very often that structural parts made of plastics are submitted to a long term loading which “jumps” periodically between a constant maximal value and a constant minimal one. The knowledge of the material response to such a kind of loading demands very laborious experimental investigations. Since generally the loading takes place in the nonlinear viscoelastic range of the material, an analysis based on linear superposition cannot be applied. In the present paper a computational method is proposed to predict the response of the polymer to a low frequency “jumping” load in the nonlinear viscoelastic range, This method is based on the knowledge of the long term behavior of the material under constant loading conditions, which is approximated by finite exponential series. Both cases, stress‐relaxation‐type and creep‐type loading histories are treated. Examples presented show a very good agreement between theoretical predictions and experimental data.