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| Titel |
Flow of pure water ice: Grain growth and deformation |
| VerfasserIn |
Sabrina Diebold, Hans De Bresser, William B. Durham, Laura Stern |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250053896
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| Zusammenfassung |
| Water ice in outer space is a significant constituent, forming icy layers and ice bodies on
moons and planets. Because of the extreme conditions on icy moons in the outer solar system,
it is essential to acquire experimental data on the deformation behaviour of ice at a wider
range of pressures and temperature than relevant for terrestrial ice. Only with a good
understanding of ice at these conditions it is possible to include the microphysics of ice in
meaningful numerical simulations. One important basis for ice flow modelling is a
deformation mechanism map including both grain-size-sensitive (GSS) flow and
grain-size-insensitive (GSI) flow. Due to dynamic recrystallization and/or grain
growth, the grain size distribution of the deforming aggregate will be modified during
deformation, resulting in a progressive change in the relative contribution of GSS and GSI
mechanisms to the overall strain rate. A deformation mechanism map helps exploring such
changes.
We studied grain size evolution both during static annealing and during deformation.
Static anneals ran for up to two weeks at 213 -¤ T -¤ 268 K and hydrostatic pressures 0.1 MPa
and 100 MPa. Static grain growth observations allow us to calibrate values for the grain size
exponent m and the activation energy Q as used in conventional grain growth laws. Axial
deformation experiments were carried out for a variety of starting grain sizes, from smaller
than 2 microns up to 250 microns, with both narrow and broad size distributions. Small grain
sizes promote GSS creep; large sizes promote GSI creep and a mixture of large and small
grains will result in mixed-mechanism deformation. All deformation runs were performed at
temperatures > 170 K, pressures ranging between 30 MPa and 100 MPa and strain rates
between 1E-08/s and 1E-04/s.
The new mechanical data of the deformation runs have been combined with data from
various previous studies, allowing us to create an updated deformation mechanism map.
Progressive changes in the microstructure appear to let the material evolve towards a steady
state balance between GSS and GSI mechanism at high strain. With the application of such
balance, modelling the flow of planetary ice would become easier than it is the case at
present. |
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