Finite deformation constitutive model for macro-yield behavior of amorphous glassy polymers with a molecular entanglement-based internal-state variable

Abstract

To describe the macro-yield behavior of amorphous glassy polymers which is significantly affected by thermo-mechanical history and deformation state, an elasto-viscoplastic constitutive model incorporating a molecular entanglement-based internal-state variable is proposed. While the classical topological entanglement governs the benchmark mechanical performances such as the pre-yield linearity and the post-yield softening plateau, the secondary short-range microstructure, named as the sub-entanglement owing to the local interaction between neighboring molecular chains, is taken as the intrinsic source of yield peak. The microstructure related deformation resistance can be decomposed into the topological entanglement related one, s˜te, and the sub-entanglement related one, s˜se, respectively. During the macro-yield procedure, s˜te is assumed as constant because the topological entanglement rarely disentangles, while s˜se evolves with the gradually dissociating sub-entanglement. The evolution equation of s˜se is presented and its physical meaning is clarified. Validated with the experimental data of amorphous glassy polymers in literature, the proposed constitutive model can not only well describe the macro-yield behavior, but also reasonably explain the effects of thermo-mechanical history and deformation state on the macro-yield behavior.