Superplastic deformation of ice: Experimental observations
TLDR
In this article, a constitutive equation based on these experimental results that includes flow laws for these four creep mechanisms is described. But this equation is in excellent agreement with published laboratory creep data for coarse-grained samples at high temperatures.Abstract:
Creep experiments on fine-grained ice reveal the existence of three creep regimes: (1) a dislocation creep regime; (2) a superplastic flow regime in which grain boundary sliding is an important deformation process; and (3) a basal slip creep regime in which the strain rate is limited by basal slip. Dislocation creep in ice is likely climb-limited, is characterized by a stress exponent of 4.0, and is independent of grain size. Superplastic flow is characterized by a stress exponent of 1.8 and depends inversely on grain size to the 1.4 power. Basal slip limited creep is characterized by a stress exponent of 2.4 and is independent of grain size. A fourth creep mechanism, diffusional flow, which usually occurs at very low stresses, is inaccessible at practical laboratory strain rates even for our finest grain sizes of approximately 3 micrometers. A constitutive equation based on these experimental results that includes flow laws for these four creep mechanisms is described. This equation is in excellent agreement with published laboratory creep data for coarse-grained samples at high temperatures. Superplastic flow of ice is the rate-limiting creep mechanism over a wide range of temperatures and grain sizes at stresses less than or equal to 0.1 MPa, conditions which overlap those occurring in glaciers, ice sheets, and icy planetary interiors.read more
Citations
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References
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Journal ArticleDOI
Diffusional Viscosity of a Polycrystalline Solid
TL;DR: In this article, it is suggested that mosaic boundaries and boundaries between grains of nearly the same orientation may not serve as sources or sinks of the diffusion currents, in which case the creep rate will depend only on the configuration of grain boundaries having a sizable orientation differen...
Journal ArticleDOI
A Model for Boundary Diffusion Controlled Creep in Polycrystalline Materials
TL;DR: In this article, the authors discussed the mechanism of creep in polycrystalline alumina based on the differences between the lattice and boundary diffusion models and showed that the boundary diffusion model is more stable than lattice diffusion model, while the grain size dependence and the numerical constant are greater.
Journal ArticleDOI
Diffusion-accommodated flow and superplasticity
M.F. Ashby,R. A. Verrall +1 more
TL;DR: In this article, a new mechanism for superplastic deformation is described and modelled, which differs fundamentally from Nabarro-Herring and Coble creep in a topological sense: grains switch their neighbors and do not elongate significantly.
Journal ArticleDOI
The creep of polycrystalline ice
TL;DR: In this article, the results of these tests are discussed in connexion with previous work on metals and ice, and also with measurements of glacier flow, showing that ice creeps in a manner similar to that shown by metals at high temperatures; there is a transient creep component and also a continuing or quasi-viscous component.
Journal ArticleDOI
On grain boundary sliding and diffusional creep
Rishi Raj,M.F. Ashby +1 more
TL;DR: In this paper, the problem of sliding at a nonplanar grain boundary is considered in detail, and the results give solutions to the following problems: 1) How much sliding occurs in a polycrystal when neither diffusive flow nor dislocation motion is possible? 2) What is the sliding rate at a wavy or stepped grain boundary when diffusional flow of matter occurs? 3) How is the rate of diffusional creep in polycrystals in which grain boundaries slide? 4) how is this creep rate affected by grain shape, and grain boundary migration? 5)