Polymer failure modeled by Molecular Dynamics

by Kristian Berg Keilen

Institution: Norwegian University of Science and Technology
Year: 2014
Record ID: 1294459
Full text PDF: http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-26248


This thesis is written as a mandatory part of the master degree program Materials Science and Engineering at NTNU, spring 2014. This thesis has been done for the Departement of Engineering Design and Materials.Molecular dynamics (MD) is a field of science that studies interactions between atoms. MD operates on very small order of magnitudes, in space with Angstroms and in time with nanoseconds. Even with these small scales it is possible to reproduce events on a macroscopic level, due to some results of thermodynamics and statistical dynamics.MD is often used to model molecules, and in this thesis we will look at a distinct phenomenon: Bond scission. The breaking of bonds can happen in many cases, but in this thesis we wish to study irreversible bond breaking as a result of large strains for polyethylene. At what bond length can we say that the bond is broken?The model that we will use is a united atom (UA) polyethylene model with covalent bonds that have bond energy given by the Morse potential. We shall attempt to find bond breaking lengths that give strains that may be comparable with experimental results, so that this model can be used in further research down the line.MD is a science that builds upon a lot of other sciences, like quantum mechanics, statistical mechanics and thermodynamics. In this thesis, I have written a comprehensive introduction to the field, both in theory and in application of computer programs like LAMMPS, in hopefully such a way that one who is not familiar with MD can get a good enough understanding of the field to do some simulations themselves.