Description
- Abstract:
- Stress-reduction, creep, grain-growth, and attenuation experiments were conducted on polycrystalline water ice to examine the links amongst microstructural steady-state, the mechanical response to transient loading, and processes of energy dissipation during grain size-sensitive (GSS) creep. The experimental conditions were chosen specifically for their relevance to geophysical processes and the evolution of icy bodies of the outer solar system, such as the Jovian moon Europa. The constant-hardness creep compliance of polycrystalline water ice, measured via stress-reduction experiments, conforms to the lambda law at high stresses. This behavior, while consistent with a dislocation rheology, has aspects unique to ice: the response deviates from the lambda law at low stresses in a manner suggestive of diffusion-creep relaxation. Microstructural observations indicate that the length scales at the heart of this behavior are associated with stress-sensitive grain boundary topography. Grain boundary processes were further explored by comparing the relative energy dissipation rates of grain growth and GSS creep. Two regimes are identified: one in which the creep dissipation rate exceeds that by grain growth, and another where the converse is true. When the energy dissipation rate by creep is higher, grain growth is inhibited. Simultaneous creep and annealing experiments on polycrystalline water ice in both regimes confirm this hypothesis. Finally, low-frequency (.0001 < ƒ [Hz] < 0.1) attenuation was measured in water ice during steady-state GSS and dislocation creep. The measured attenuation response is linear, indicating a diffusional mechanism, and exhibits a power-law spectrum that is more attenuating than predicted by standard models. In ice deforming via dislocation creep, an absorption peak arises due to elastically-accommodated grain boundary sliding, associated with the (stress-sensitive) length scale of the subgrain size and broader than a Debye peak due to a distribution of subgrain sizes. In ice deforming via GSS creep, the attenuation spectra are more absorptive across a broad range of frequencies above ~10 3 Hz. This response indicates that fundamental assumptions regarding grain boundary processes in current models of (high-temperature background) attenuation break down when the material is simultaneously deforming in a regime that is rate-limited by the grain boundary viscosity.
- Notes:
- Thesis (Ph. D.)--Brown University, 2017
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Citation
Caswell, Tess Elaina,
"Grain Boundaries, Deformation and Energy Dissipation in Water Ice"
(2017).
Earth, Environmental and Planetary Sciences Theses and Dissertations.
Brown Digital Repository. Brown University Library.
https://doi.org/10.26300/6b96-ne11
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Earth, Environmental and Planetary Sciences Theses and Dissertations
Theses and Dissertations for the Earth, Environmental and Planetary Sciences department....