Characterization and prediction of the nonlinear creep behavior of 3D-printed polyurethane acrylate

While the potential application of 3D-printed polymers is remarkable because of the favorable mechanical properties of these materials and their feasibility for producing customized structural components, 3D-printed polymer materials are rarely used in load-bearing structures due to a lack of understanding of the mechanical behaviors of a printed part over a long service life. In this study, the creep behaviors of ultraviolet-curable polyurethane acrylate (UV-PUA) fabricated by using a digital light processing 3D printer was investigated through experimental testing and finite element simulations. Digital image correlation was used to monitor the creep deformations under various thermomechanical conditions. A one-dimensional creep constitutive model was developed to characterize the nonlinear viscoelastic responses of the 3D-printed UV-PUA by decoupling temperature and stress effects. The constitutive model was further implemented in an ABAQUS UMAT subroutine. The simulation results show that the numerical creep model describes well the creep deformations and predicts a reasonable creep life at low temperatures. The sensitivity of the creep behavior of the printed specimens to various types of initial damage was also studied using the developed constitutive model, and the model results were validated by the tensile test results. The results are in good agreement, which verifies the feasibility of numerical method implemented in UMAT for studying the mechanical properties of 3D printed polymers.