Nonlinear time-dependent behavior of rheodictic polymersOseli, Alen (Avtor) Mihelčič, Mohor (Avtor) Šobak, Matic (Avtor) Slemenik Perše, Lidija (Avtor) rheodictic polymersnonlinear behaviortime-dependent mechanical propertiescreep processSchapery’s nonlinear modelThe present study examined the nonlinear time-dependent behavior of rheodictic polymers, a class of noncrosslinked materials that exhibit flow. Such behavior was addressed with extended Schapery’s nonlinear viscoelastic model by introducing new physical quantities, i.e., the flow term Φ$_{flow}$ and corresponding nonlinear shift parameter g$_{2,flow}$. While Φ$_{flow}$ portrays irrecoverable deformation, g$_{2,flow}$ depicts a nonlinear contribution to flow acceleration. This theory was accompanied by analytical and experimental methodologies for identifying all the parameters in the linear and nonlinear viscoelastic domains. Predictions of long-term time-dependent behavior (in shear) at various stress states show excellent agreement with the experimental data, i.e., within 5% error, obtained for polycarbonate at 130 °C. Surprisingly, the newly introduced g$_{2,flow}$ indicates that flow retardation occurs with increasing stress, implying that a highly deformed entangled system hinders molecular reptation/disentanglement. Nevertheless, the proposed extension of Schapery’s nonlinear viscoelastic model not only allows accurate predictions of the nonlinear time-dependent behavior of rheodictic polymers but also enables a detailed outlook on the underlying molecular mechanisms under severe environmental and loading conditions.20242024-07-31 10:23:05Članek v reviji159934sl