A predictive method for the nonlinear viscoelastic characterization of carbon/epoxy fibre composites

In the present work, a method for the characterization of the nonlinear viscoelastic response of a UD/90° carbon/epoxy composite is presented. Based on the characteristic creep-recovery response of the material, both analytical and numerical expressions for the nonlinear parameters included in the Schapery”s constitutive thermodynamic equation were developed. The viscoplastic response developed during creep is also taken into account. For the full viscoelastic characterization of the material under consideration, creep-recovery tests at different applied stress levels were conducted. A generic function for the prediction of the variation of all the four parameters with the applied stress was developed. A minimum number of experimental data for the prediction of the nonlinear parameters is needed.