M Mikhail Poluektov

Micromechanical modelling of short-term and long-term large-strain behaviour of polyethylene terephthalate

A micromechanically based model is used to describe the mechanical behaviour of polyethylene terephthalate (PET) under uniaxial compression up to large strains and at different temperatures. The creep behaviour of isotropic PET is simulated and compared to experimental data to demonstrate the applicability of the model to describe the long-term response. The material is modelled as an aggregate of two-phase layered domains, where different constitutive laws are used for the phases. A hybrid interaction law between the domains is adopted. The crystalline phase is modelled with crystal plasticity and the amorphous phase with the Eindhoven Glassy Polymer model, taking into account material ageing effects. Model parameters for the selected constitutive laws of the phases are identified from uniaxial compression tests for fully amorphous material and semicrystalline material. Texture evolution during the deformation predicted by the model adequately matches previously observed texture evolution.

Characterisation and modelling of anisotropic thermo-mechanical behaviour of oriented polyethylene terephthalate

The long-term and short-term anisotropic mechanical behaviour of a biaxially stretched polyethylene terephthalate foil is measured. The orientation of the crystalline phase is characterized and the representative foil microstructure is discussed. Using the obtained information, a mean-field model is used to simulate the elasto-viscoplastic behaviour of the oriented polymer foil, taking into account the different constitutive behaviour of the phases. The material is modelled as an aggregate of connected two-phase domains. The parameters of the constitutive behaviour of the crystalline and non-crystalline phases have been determined, and the ability to simulate the large-strain anisotropic behaviour of polyethylene terephthalate in the strain-rate-controlled regime and the long-term creep has been demonstrated. The model is extended to include pre-orientation of the non-crystalline phase. In addition, deformation at the microscopic level is analysed using the model results.

Atomistic-continuum multiscale modelling of magnetisation dynamics at non-zero temperature

In this article, a few problems related to multiscale modelling of magnetic materials at finite temperatures and possible ways of solving these problems are discussed. The discussion is mainly centred around two established multiscale concepts: the partitioned domain and the upscaling-based methodologies. The major challenge for both multiscale methods is to capture the correct value of magnetisation length accurately, which is affected by a random temperature-dependent force. Moreover, general limitations of these multiscale techniques in application to spin systems are discussed.