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- Wilson, Christopher J.L., et al.
(författare)
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Deformation of polycrystalline D2O ice: Its sensitivity to temperature and strain-rate as an analogue for terrestrial ice
- 2020
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X. ; 532
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline deuterated ice (D2O) was deformed over a range of high-temperatures (−20 to −1 °C; 0.92–0.99Tm) during in situ neutron diffraction texture and grain-size analysis. This allowed for a continuous monitoring of the evolution of rheology, texture, grain-numbers and the type of microstructures, which are compared to those encountered in basal sections of ice-sheets. We quantify the textural evolution with J-index changes as a function of strain-rate and temperature. Three sets of unconfined samples were deformed at displacement rates of 1×10−5 s−1 (fast) 2.5×10−6 s−1 (medium) and 6×10−7 s−1 (slow). Dislocation creep is proposed as the main deformation mechanism with sub-grain rotation more significant at lower temperatures (0.92Tm) and/or higher strain-rates. At higher-temperatures (0.99Tm) and/or lower strain-rates dynamic recrystallization is dominated by grain boundary migration, typified by grains with highly curved or lobate grain boundaries, and leading to rheological softening of the ice. From initially randomly oriented [c]-axes, a texture comprising 30–35° cones parallel to the compression axis develops, which is comparable to textures observed in the upper levels of polar ice-sheets. There is also a strain-rate dependence on the development of normalized [c]-axis intensities, which is in competition with strain magnitude and temperature. At lower temperatures (≤10 °C), small increments of strain or slower strain-rates, the cone-angle and textural strength decrease with a dominant textural component parallel to the compression axis. This may be an explanation for the vertical [c]-axis concentrations observed in polar ice cores.
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| 2. |
- Wilson, Christopher J.L., et al.
(författare)
-
Partial melting in polycrystalline ice: pathways identified in 3D neutron tomographic images
- 2024
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Ingår i: Cryosphere. - 1994-0416 .- 1994-0424. ; 18:2, s. 819-836
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Tidskriftsartikel (refereegranskat)abstract
- In frozen cylinders composed of deuterium ice (Tm+3.8C) and 10% water ice (Tm0C), it is possible to track melt pathways produced by increasing the temperature during deformation. Raising the temperature to +2C produces water (H2O) which combines with the D2O ice to form mixtures of HDO. As a consequence of deformation, HDO and H2O meltwater are expelled along conjugate shear bands and as compactional melt segregations. Melt segregations are also associated with high-porosity networks related to the location of transient reaction fronts where the passage of melt-enriched fluids is controlled by the localized ductile yielding and lowering of the effective viscosity. Accompanying the softening, the meltwater also changes and weakens the crystallographic fabric development of the ice. Our observations suggest meltwater-enriched compaction and shear band initiation provide instabilities and the driving force for an enhancement of permeability in terrestrial ice sheets and glaciers.
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