Numerical Study of the Nonlinear Viscoelastic Creep Behavior of a Mirror Epoxy Resin

This work presents a numerical validation of the nonlinear viscoelastic creep behavior of a mirror epoxy resin using the Schapery model. The material parameters were identified from experimental creep tests conducted under several constant stress levels. The Schapery creep formulation was implemented into the Abaqus finite element framework through a user-defined material subroutine (UMAT) and applied to a representative numerical model to reproduce the experimental loading conditions. The simulated creep strain evolutions show good agreement with the experimental results over the entire loading duration. Quantitative comparisons reveal low average errors (approximately 1.5-3%), high coefficients of determination (R2 > 0.90), and moderate dispersion, confirming the robustness of the identified parameters. These results demonstrate the capability of the UMAT-based Schapery creep model to accurately capture the nonlinear time-dependent response of the epoxy resin under sustained loading. The proposed approach provides a reliable basis for predicting long-term viscoelastic creep behavior in polymer-based structural applications.