ONLINE-Seminar für Mechanik

05. 05. 2021 | 13.00 Uhr - 14.30 Uhr

Vortragender: Prof. Dr.-Ing. habil. Thomas Böhlke vom Karlsruher Institut für Technologie (KIT)

Vortragsthema: "Laminat-basierte Modellierung semi-kristalliner Polymere“

Autoren: Thomas Böhlke (Prof. Dr.-Ing., Universitätsprofessor, Vortragender), Sebastian Gajek (M.Sc.), Johannes Ruck (Dr.-Ing.), Philipp Kloza (M.Sc.)


Semicrystalline polymers such as, e.g., polyethylene or polyethylene terephthalate, are omnipresent in engineering applications. These polymers exhibit spatially distinct regions of amorphous and crystalline phases. Due to differing thermo-mechanical material behavior of each phase, the material's microstructure has a pronounced influence on the effective properties of the material. The microstructure is mainly determined by the thermo-mechanical manufacturing process. Additionally, temperature and loading history can influence phase composition, as well, such that modeling phase and glass transitions need to take these aspects into account.

The work at hand covers the phase and glass transition behavior of semicrystalline polymers based on a micromechanical model. To this end, the microstructure is idealized as a three-phase, rank-one laminate model in order to model first- and second-order phase transitions subject to small strains. The laminate model is set up on previous works [1] and enables the consideration of the polymer microstructure as well as stress and strain localization. The three-phase laminate model consists of a crystalline phase, a rigid amorphous phase and a mobile amorphous phase [2]. Additionally, glass transition effects are taken into account employing a phenomenological approach from the literature [1]. Using a thermodynamically consistent continuum model, the phase transition can be described by the movement of singular surface boundaries inside the laminate structure. As a first approximation, the shear viscosity is not considered and the material behavior is assumed to be isotropic. The phase transition in the thermodynamic equilibrium is considered as a process that minimizes the free Helmholtz energy of the laminate with respect to the volume fractions, the orientation of the phase boundaries as well as the internal variable describing glass transition effects. In order to simulate the interface kinetics in non-equilibrium cases, phenomenological evolution equations are taken from the literature [1] to describe non-equilibrium phase and glass transitions.

Numerical simulations demonstrate that the three-phase laminate model is able to qualitatively represent temperature and deformation-history dependent crystallization under consideration of glass transition effects.

[1] Lion, A., Johlitz, M., 2015. A thermodynamic approach to model the caloric properties of semicrystalline polymers. Continuum Mechanics and Thermodynamics 28 (3), 799--819.
[2] Wunderlich, B., 2003. Reversible crystallization and the rigid-amorphous phase in semicrystalline macromolecules. Progress in Polymer Science 28 (3), 383--450.


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