Micromechanics of semicrystalline polymers: Yield kinetics and long‐term failure

Abstract

The process of plastic deformation in semicrystalline polymers is complicated due to the operation of a variety of mechanisms at different levels and is strongly dependent on their underlying microstructure. The objective of this work is to establish a quantitative relation between the microstructure and the mechanical performance of semicrystalline polymers, as characterized by elasto-viscoplastic deformation. To do that, a micromechanically based constitutive model is used. The model describes the material as an aggregate of two-phase layered composite inclusions, consisting of crystalline lamellae and amorphous layers. The starting point for adding quantitative abilities to the model, in particular for the yield kinetics, is formed by experimental observations on both the yield kinetics and the time-to-failure of polyethylene at different temperatures, which reveal the contribution of two relaxation processes. To predict the thermo-rheologically complex short-term and long-term failure behavior, the crystallographic slip kinetics and the amorphous yield kinetics are re-evaluated, and the Eyring flow rule is modified by adding a temperature shift function. To enable the prediction of both tension and compression, a non-Schmid effect is added to the constitutive relation of each slip system. The creep behavior of polyethylene is then simulated directly using the multiscale, micromechanical model, predicting the time-tofailure, controlled by plastic deformation.

The prediction of mechanical performance of isotactic polypropylene on the basis of processing conditions

“…5(b). At high temperatures or low strain rates, only the process of crystal slip or intra-lamellar deformation determines the yield stress [54]. At lower temperatures, crystal slip or inter-lamellar deformation starts to actively contribute to the observed yield stresses [55].…”

Micromechanical modelling of reversible and irreversible thermo-mechanical deformation of oriented polyethylene terephthalate

“…A similar dependence of crystallographic slip on temperature was also included in a micromechanical model of HDPE in [17]. The influence of viscoelastic hardening of the non-crystalline phase and thermal dependence of the slip kinetics on the macroscopic behaviour obtained with the composite inclusion model is shown in Fig.…”

“…The elastic behaviour of the crystalline phase is anisotropic. The viscoplastic deformation is a superposition of shear deformations on a limited number of crystallographic slip systems with an Eyring flow equation relating shear rate and resolved shear stress [17,27].…”

“…In this article, the effect of shape recovery of a PET film is modelled using a micromechanical model referred to as the composite inclusion model [14][15][16][17][18]. In this model, the material is considered to consist of two phases: the crystalline and the amorphous phases, out of which layered domains are constructed.…”

Through-Process Modelling for Accurate Prediction of Long Term Anisotropic Mechanics in Fibre Reinforced Thermoplastics.

“…Micromechanically based constitutive models [7,8] are powerful tools, which enable establishing a relation between mechanical properties of FRTP materials and their underlying morphology including being fiber volume fraction, aspect ratio and orientation. Recently, some of these models have been adapted and implemented in several commercial software, which allow their utilization in industrial applications.…”