Multiscale Simulation of Polymers - Coupling of Continuum Mechanics and Particle-Based Modelling

Pfaller S (2015)


Publication Language: English

Publication Type: Thesis

Publication year: 2015

Publisher: University of Erlangen-Nuremberg

Edited Volumes: Schriftenreihe Technische Mechanik

City/Town: Erlangen, Germany

ISBN: 2190-023X

DOI: 10.25593/opus4-fau-18062

Abstract

In modern engineering applications, plastics play an important role for instance in the field of lightweight constructions or as substitutes for classical materials like wood, metal, or glass. Typically, they consist of organic polymers, which are long-chained molecules comprising numerous monomers as repeat units. In addition, polymers frequently contain fillers, plasticisers, or colourants to achieve and to adjust specific properties. In recent years, new techniques have been established to produce and to disperse filler particles in the range of nanometres, which corresponds to the typical dimensions of the monomers. Experiments reveal that these so-called “nanofillers” may significantly toughen polymers, improve their fatigue lifetime, and enhance control of their thermodynamical properties, even for low filler contents in terms of mass or volume. This cannot be explained by a simple rule of mixture, but is traced back to the very large ratio of surface to volume in case of nanofillers and to the associated processes at the molecular level. The effective design of such “nanocomposites” is demanding and often requires timeconsuming mechanical testing. For a better understanding of the relevant parameters and in order to improve the process of material development, it is beneficial to substitute “real” experiments by numerical simulations. To this end, sophisticated computation techniques are required that account for the specific processes taking place at the level of atoms and molecules. Particle-based strategies, as for instance employed in physical chemistry, are able to consider the atomistic structure in detail and thus permit to simulate material behaviour at atomistic length scales. However, it is still not possible to apply these techniques to large-scale systems relevant in engineering. There, the material behaviour of structures is typically described by continuum approaches, which, on the other hand, cannot account explicitly for the processes at the atomistic level. To overcome this, the present thesis proposes a novel coupling scheme to incorporate particle-based simulations into continuum-based methods. In particular, it links molecular dynamics as a standard tool in physical chemistry with the finite element method, which is nowadays widely used in engineering applications. This multiscale simulation approach has been developed jointly by the Theoretical Physical Chemistry Group at the Technische Universität Darmstadt and the Chair of Applied Mechanics at the Friedrich-Alexander-Universität Erlangen-Nürnberg. Thus, it bases upon expertise in atomistic simulation as well as continuum mechanics, whereby crucial modifications of established techniques in both fields had to be developed. Two sample systems, modelling pure polystyrene and a polystyrene-silica nanocomposite, are studied numerically and prove the suitability of the new approach. In this context, various parameters of the proposed method and its implementation are investigated. Based on this, a number of options to improve this multiscale technique are discussed and relevant issues for future research are summarised.

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How to cite

APA:

Pfaller, S. (2015). Multiscale Simulation of Polymers - Coupling of Continuum Mechanics and Particle-Based Modelling (Dissertation).

MLA:

Pfaller, Sebastian. Multiscale Simulation of Polymers - Coupling of Continuum Mechanics and Particle-Based Modelling. Dissertation, Erlangen, Germany: University of Erlangen-Nuremberg, 2015.

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