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 Unpublished PhD dissertation,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
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