| dc.description.abstract | The focus of this thesis has been to use large-scale atomistic simulations to increase the
understanding of fracture processes at the atomistic level. The Large-scale Atomic/Molecular
Massively Parallel Simulator (LAMMPS) has been run on the supercomputer Vilje, at the NOTUR
centre at NTNU. The atomistic models were fully 3D, notched micro-cantilever structures
in bcc-Fe, modeled to resemble micro sized fracture mechanics structures tested in literature.
The EAM potential "Mendelev II" has been applied, having been shown to be fairly accurate
for dislocations while also computationally cheap enough for the systems to be simulated.
Simulations on atomistically sharp cracks in bcc-Fe were carried out in Paper I, and a
novel crack flange extrapolation method first used to calculate the plastic zone size in order
to estimate the stress intensity in cracks in Si was applied. The stress intensity factors found
using the crack flange extrapolation method was found to give reasonable estimates in iron,
but more investigation would be necessary to establish this method as a robust measure of
fracture toughness.
Paper II simulates the strain rate effect for sharp and blunted crack tips in pentagonal
cross-section cantilevers in bcc-Fe. The rounded crack tip is shown to reproduce experimentally
observed crack behavior more accurately than the sharp crack tip. The crack flange extrapolation
method is applied, with estimates for fracture toughness using this method showing
a more realistic trend than continuum based fracture toughness calculations. A brief postdeformation
comparison between simulations and SEM-images of Focused Ion Beam-fabricated
micro-cantilevers was also done, showing possible signs of similar deformation mechanisms and
dislocation systems between them.
Four different orientations for notched cantilevers were studied in simulations, and the
crack behavior was compared to existing literature in Paper III. The crack flange extrapolation
method was used to calculate fracture toughness, and was found to better reflect the qualitative
behavior during crack initiation than estimates from continuum based fracture mechanics. FIBfabricated
notched cantilever beams with initial (100)[0¯11] crack system loaded experimentally,
and examined using Transmission Electron Microscopy (TEM), showed a local brittle fracture
consistent with results from the modeling. | nb_NO |
