Experiments on the Deformation of Ice

Glen, J. W.

doi:10.1017/s0022143000034067

Cited by 185 publications

(104 citation statements)

References 8 publications

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“…To date, the flow of glaciers and ice sheets has generally been modeled using the Glen flow law, a power law relation based on the pioneering laboratory experiments of Glen [1952Glen [ , 1955 previous laboratory data, we extrapolate our constitutive equation to the larger grain sizes and higher temperatures used in most laboratory creep experiments. Three further refinements are first required to take into account the increase in the apparent activation energy for dislocation creep at higher temperatures, the rate of diffusional flow, and the enhancement in the diffusional flow rate due to premelting.…”

Section: New Constitutive Equationmentioning

confidence: 99%

Superplastic deformation of ice: Experimental observations

Goldsby

Kohlstedt²

2001

J. Geophys. Res.

591

848

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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 climblimited, 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--3 •m. 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 • 0.1 MPa, conditions which overlap those occurring in glaciers, ice sheets, and icy planetary interiors.

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Section: New Constitutive Equationmentioning

confidence: 99%

Superplastic deformation of ice: Experimental observations

Goldsby

Kohlstedt²

2001

J. Geophys. Res.

591

848

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“…The pioneering work of Glen (1952Glen ( , 1953Glen ( , 1955Glen ( , 1958 and Steinemann (1954) established the power law form of the flow relation for ice, largely from separate series of tests on polycrystalline ice with randomly oriented crystals, in either unconfined compression or simple shear. Although they recognized that higher tertiary strain rates and anisotropy developed at high strains, the relations for secondary flow rates for isotropic ice tended to be used as the standards against which studies of the flow of natural ice masses were compared.…”

Section: The Historical Basis For the Flow Law Of Ice Developed From mentioning

confidence: 99%

Ice flow relations for stress and strain-rate components from combined shear and compression laboratory experiments

et al. 2013

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ABSTRACT. The generalized (Glen) flow relation for ice, involving the second invariants of the stress deviator and strain-rate tensors, is only expected to hold for isotropic polycrystalline ice. Previous single-stress experiments have shown that for the steady-state flow, which develops at large strains, the tertiary strain rate is greater than the minimum (secondary creep) value by an enhancement factor which is larger for shear than compression. Previous experiments combining shear with compression normal to the shear plane have shown that enhancement of the tertiary octahedral strain rate increases monotonically from compression alone to shear alone. Additional experiments and analyses presented here were conducted to further investigate how the separate tertiary shear and compression strain-rate components are related in combined stress situations. It is found that tertiary compression rates are more strongly influenced by the addition of shear than is given by a Glen-type flow relation, whereas shear is less influenced by additional compression. A scalar function formulation of the flow relation is proposed, which fits the tertiary creep data well and is readily adapted to a generalized form that can be extended to other stress configurations and applied in ice mass modelling. BACKGROUNDIn natural ice masses the most important and common state of deformation is arguably a combination of approximately bed-parallel shear and vertical compression. For deformational flow with a stationary boundary, a region of simple shear is associated in an essential way with bulk transport of ice in glaciers, ice sheets and ice shelves, and this is generally accompanied by normal deformations associated with increasing velocities along the flow and divergence or convergence transverse to the flow.For a coordinate system with x and y horizontal and z vertical, and corresponding component velocities (u, v, w), simple shear deformation in the x direction can be characterized by du/dz = c where we note that the horizontal planes on which the forces generating shear deformation act do not rotate, while compression normal to these planes is described by dw/dz = k, where c/2 and k are the respective shear and vertical compressive strain rates. The compressive flow may be confined or unconfined, and quite generally the accompanying horizontal normal strain rates are du dx ¼ ð À 1Þk and dv dy ¼ Àk where the factors involving indicate the proportions of the deformations in the horizontal directions, relative to the rate of vertical compression. Note that = 1/2 corresponds to uniaxial compression in the z direction, while = 1 corresponds to longitudinally confined compression in the experiments reported here (Fig. 1).The generalized flow relation for ice involving the second invariants of the stress deviator and strain-rate tensors (Nye, 1953;Glen, 1958) provides a useful formulation for the interactions between the individual stress and strain-rate components for isotropic ice. This relation is not expected to apply for anisotropic i...

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“…Values of the exponent n in (5) and (6) pioneering work, Glen (1952) found n = 4. After extending his preliminary re-414 sults, he came to n = 3.2 (Glen, 1955).…”

mentioning

confidence: 95%

“…sued by Glen (1952Glen ( , 1955, by determining a power-law relation between the min-371 imum strain rate actually observed in experiments and the stress required to pro-372 duce it. In its most popular version (due to Nye, 1953) …”

mentioning

confidence: 99%

The microstructure of polar ice. Part II: State of the art

Faria

Weikusat

Azuma

2014

Journal of Structural Geology

110

189

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Besides the obvious relevance of glaciers and ice sheets for climate-related issues, another important feature of natural ice is its ability to creep on geological time scales and low deviatoric stresses at temperatures very close to its melting point, without losing its polycrystalline character. This fact, together with its strong mechanical anisotropy and other notable properties, makes natural ice an interesting model material for studying the high-temperature creep and recrystallization of rocks in Earth's interior. After having reviewed the major contributions of deep ice coring to the research on natural ice microstructures in Part I of this work (Faria et al., this issue), here in Part II we present an up-to-date view of the modern understanding of natural ice microstructures and the deformation processes that may produce them. In particular, we analyse a large body of evidence that reveals fundamental flaws in the widely accepted tripartite paradigm of polar ice grains is also observed at various depths, provided that the local concentration of strain energy is high enough (which is not seldom the case). As a substitute for the tripartite paradigm, we propose a novel dynamic recrystallization diagram in the three-dimensional state space of strain rate, temperature, and mean grain size, which summarizes the various competing recrystallization processes that contribute to the evolution of the polar ice microstructure.

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Experiments on the Deformation of Ice

Cited by 185 publications

References 8 publications

Superplastic deformation of ice: Experimental observations

Superplastic deformation of ice: Experimental observations

Ice flow relations for stress and strain-rate components from combined shear and compression laboratory experiments

The microstructure of polar ice. Part II: State of the art

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