ABSTRACT
In-situ observations of a deforming aggregate of the hexagonal
material octachloropropane have been analysed. Calculations of
micro-strains and measurement of c-axis orientations have enabled
the processes influencing fabric development to be distinguished,
and the importance of dynamic grain boundary migration to be
assessed. It was found that in this material, inter-grain strain
contrasts could be significant, and that the effect of grain
boundary migration was to modify the fabric in a measurable way. A
simple model for the driving force for grain boundary migration
based on dislocation density contrasts, as controlled by
intra-grain strains and grain orientations, is proposed and tested
and can account for the migration direction of most of the
observed boundaries.
Several grain-scale microstructures are described that demonstrate
the migration direction of once-mobile grain boundaries in a
naturally deformed quartzite. I present an analysis of the sense
of migration of the boundaries and the characteristics of the
patterns of relative grain growth and shrinkage. Grain boundary
migration can be correlated with the relative crystallographic
orientations of neighbouring grains.
A new computer simulation of the development of grain shape and
crystallographic preferred orientations is presented. This model
combines homogeneous strains, simplified versions of the lattice
rotations predicted by Taylor-Bishop-Hill theory, mobile grain
boundaries and the nucleation of new grains, and allows the
progressive development of the fabrics to be followed. The model
generates several commonly measured quartz c-axis fabrics, while
at the same time predicting characteristic variations in average
grain sizes and the intensity of grain shape fabrics that arise
from differing recrystallization regimes and strain geometries.
Jessell, M.W., 1986. Dynamic grain boundary migration and fabric
development: observations, experiments and simulations.
Unpublished PhD dissertation, State University of New York at
Albany. 270pp., +xv
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 1986 J48
Copies of this PhD dissertation can be ordered
from Proquest UMI
Front matter (title,
table of contents, abstract, acknowledgements) - 0.3MB pdf
file
Photo pages in dissertation
(colour
and
greyscale photos with captions): - 6.4MB pdf file
Return to PhD dissertations completed
in the Geological Sciences Program, University at Albany