Viscoelastic-viscoplastic modeling of epoxy based on transient network theory

Abstract

The expansion of the application of polymers instead of metals has warranted the evaluation and modeling of their mechanical behaviors under various conditions. In the present study, the strain-rate- and temperature-dependent nonlinear mechanical behavior of a glassy polymer from small to large strain ranges is investigated experimentally and numerically. The effects of strain rate and temperature on the mechanical responses and development of the strain field under monotonic and cyclic uniaxial tensile tests of epoxy are evaluated experimentally. In addition, the stress relaxation test is performed to evaluate the time-dependent mechanical behavior of epoxy. In the previous work (Uchida et al. 2019), the concept of the transient network (TN) theory was applied to demonstrate the nonlinear behavior of the thermosetting glassy polymer. In this model, the time-dependent mechanical behavior of the thermosetting glassy polymer was assumed to be characterized by the debonding and rebonding of intermolecular secondary bonds (SBs). In the present study, the TN model is extended to represent the temperature- and strain rate-dependent mechanical behavior of the thermosetting glassy polymer below the glass transition temperature Tg. The decrease in the deformation resistance of a polymer at a higher temperature is represented by a decrease in the SB density. Furthermore, the fixation parameter is introduced to accurately predict the residual strain in the cyclic tensile test. The mechanical responses in the monotonic and cyclic tensile tests and the stress relaxation test predicted by the extended TN model are consistent with the experimental results. The proposed model is further verified using additional experimental results provided in references. The obtained results demonstrate the nonlinear deformation behaviors of glassy polymers under wide ranges of temperature and strain rate.