Crystallographic preferred orientations of ice deformed in direct-shear experiments at low temperatures
<p>Synthetic polycrystalline ice was sheared at temperatures of <span class="inline-formula">−5</span>, <span class="inline-formula">−20</span> and <span class="inline-formula">−30</span> <span class="inline-f...
| Main Authors: | , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-02-01
|
| Series: | The Cryosphere |
| Online Access: | https://www.the-cryosphere.net/13/351/2019/tc-13-351-2019.pdf |
| Summary: | <p>Synthetic polycrystalline ice was sheared at temperatures of <span class="inline-formula">−5</span>, <span class="inline-formula">−20</span> and
<span class="inline-formula">−30</span> <span class="inline-formula"><sup>∘</sup></span>C, to different shear strains, up to <span class="inline-formula"><i>γ</i>=2.6</span>,
equivalent to a maximum stretch of 2.94 (final line length is 2.94 times the
original length). Cryo-electron backscatter diffraction (EBSD) analysis shows
that basal intracrystalline slip planes become preferentially oriented
parallel to the shear plane in all experiments, with a primary cluster of
crystal <span class="inline-formula"><i>c</i></span> axes (the <span class="inline-formula"><i>c</i></span> axis is perpendicular to the basal plane)
perpendicular to the shear plane. In all except the two highest-strain
experiments at <span class="inline-formula">−30</span> <span class="inline-formula"><sup>∘</sup></span>C, a secondary cluster of <span class="inline-formula"><i>c</i></span> axes is
observed, at an angle to the primary cluster. With increasing strain, the
primary <span class="inline-formula"><i>c</i></span>-axis cluster strengthens. With increasing temperature, both
clusters strengthen. In the <span class="inline-formula">−5</span> <span class="inline-formula"><sup>∘</sup></span>C experiments, the angle between
the two clusters reduces with strain. The <span class="inline-formula"><i>c</i></span>-axis clusters are elongated
perpendicular to the shear direction. This elongation increases with
increasing shear strain and with decreasing temperature. Highly curved grain
boundaries are more prevalent in samples sheared at higher temperatures. At
each temperature, the proportion of curved boundaries decreases with
increasing shear strain. Subgrains are observed in all samples.
Microstructural interpretations and comparisons of the data from
experimentally sheared samples with numerical models suggest that the
observed crystallographic orientation patterns result from a balance of the
rates of lattice rotation (during dislocation creep) and growth of grains by
strain-induced grain boundary migration (GBM). GBM is faster at higher
temperatures and becomes less important as shear strain increases. These
observations and interpretations provide a hypothesis to be tested in further
experiments and using numerical models, with the ultimate goal of aiding the
interpretation of crystallographic preferred orientations in naturally
deformed ice.</p> |
|---|---|
| ISSN: | 1994-0416 1994-0424 |