A physically-based thermo-mechanical model for stretch-induced crystallizable rubbers: Crystallization thermodynamics and chain-network crystallization anisotropy

摘要

In this paper, a physically-based constitutive model, considering the crystallization micromechanism at the chain-scale, is formulated within the framework of continuum thermodynamics. The stretch-induced formation of crystallized segments in the molecular chain is regarded as an irreversible thermodynamic process accompanied with energy dissipation. The microsphere-based strategy is employed to realize the transition from chain-scale to macro-scale, and to account for the crystallization anisotropy induced by the preferred network orientation. The two antagonist phenomena, i.e. the crystallization-induced softening and stiffening, are well reproduced by controlling the spatial orientation and form of the crystallized segments at the chain-scale. The micro-macro constitutive model, fully tridimensional, is implemented into a finite element program and a quantitative evaluation of the model is performed by comparisons with a few illustrative experiments. A fairly well agreement of the model is shown with tensile experiments under stretching/recovery, in terms of stress-stretch curves and crystallization kinetics, at different stretch levels and temperatures. To illustrate further the capability of the model, numerical simulations are compared to experimental non-homogeneous tensile response in terms of local crystallization/orientation fields of a specimen containing cracks.