Competition between grain growth and grain-size reduction in polar ice

Roessiger, Jens; Bons, Paul D.; Griera, Albert; Jessell, Mark; Evans, Lynn; Montagnat, Mâurine; Kipfstuhl, Sepp; Faria, Sérgio H.; Weikusat, Ilka

doi:10.3189/002214311798043690

Cited by 27 publications

(41 citation statements)

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“…It should be noted that new HAGB's are not treated as such numerically in the recrystallisation routine. This would reduce the increase in grain shape and grain size by dividing up grains (Roessiger et al, 2011;Mathiesen et al, 2004). Depending on the orientation of the new grain boundaries, average elongation could be either strengthened or weakened.…”

Section: Grain Morphology and Strain Distributionmentioning

confidence: 99%

“…The deformation-induced lattice rotation and the estimation of geometrically necessary dislocation densities calculated from the stress and velocity fields provided by the VPFFT algorithm are used to simulate intra-crystalline recovery and grain boundary migration. The ELLE platform has previously been used to simulate several deformation microstructure processes, including grain growth (Roessiger et al, 2011), dynamic recrystallisation (Piazolo et al, 2002), strain localisation or folding (Llorens et al, 2013a;2013b). In this study, grain boundary migration and recovery processes are used in order to simulate the microstructural evolution by recrystallisation.…”

Section: Numerical Proceduresmentioning

confidence: 99%

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Full-field predictions of ice dynamic recrystallisation under simple shear conditions

Llorens

Griera

Bons

et al. 2016

Earth and Planetary Science Letters

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Understanding the flow of ice on the microstructural scale is essential for improving our knowledge of large-scale ice dynamics, and thus our ability to predict future changes of ice sheets. Polar ice behaves anisotropically during flow, which can lead to strain localisation. In order to study how dynamic recrystallisation affects to strain localisation in deep levels of polar ice sheets, we present a series of numerical simulations of ice polycrystals deformed under simple-shear conditions. The models explicitly simulate the evolution of microstructures using a full-field approach, based on the coupling of a viscoplastic deformation code (VPFFT) with dynamic recrystallisation codes. The simulations provide new insights into the distribution of stress, strain rate and lattice orientation fields with progressive strain, up to a shear strain of three. Our simulations show how the recrystallisation processes have a strong influence on the resulting microstructure (grain size and shape), while the development of lattice preferred orientations (LPO) appears to be less affected. Activation of non-basal slip systems is enhanced by recrystallisation and induces a strain hardening behaviour up to the onset of strain localisation and strain weakening behaviour. Simulations demonstrate that the strong intrinsic anisotropy of ice crystals is transferred to the polycrystalline scale and results in the development of strain localisation bands than can be masked by grain boundary migration. Therefore, the finite-strain history is non-directly reflected by the final microstructure. Masked strain localisation can be recognised in ice cores, such as the EDML, from the presence of stepped boundaries, microshear and grains with zig-zag geometries.

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Section: Grain Morphology and Strain Distributionmentioning

confidence: 99%

Section: Numerical Proceduresmentioning

confidence: 99%

Full-field predictions of ice dynamic recrystallisation under simple shear conditions

Llorens

Griera

Bons

et al. 2016

Earth and Planetary Science Letters

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“…Elle was applied in various studies on ice microstructures, such as single and polyphase grain-growth (Roessiger et al, 2011(Roessiger et al, , 2014. The fullfield crystal viscoplasticity code (VPFFT) by Lebensohn (2001) coupled to Elle was used to simulate strain localisation, dynamic recrystallization and folding in ice with and without air bubbles Jansen et al, 2016;Llorens et al, 2016a,b;Steinbach et al, 2016).…”

Section: The Elle Modeling Platformmentioning

confidence: 99%

“…Breton et al (2016) report grain dissection in deformation experiments on laboratory-prepared ice and suspect a grain-size-reducing character. So far, it is assumed that stable grain sizes in ice are achieved by an interplay of dynamic graingrowth, polygonisation and potentially nucleation processes (Alley et al, 1995;De La Chapelle et al, 1998;Montagnat and Duval, 2000;Mathiesen et al, 2004;Roessiger et al, 2011;Chauve et al, 2017;Hidas et al, 2017). However, in rock analogs and bischofite, grain dissection is observed as an effective grain-sizereducing process, in particular at steady-state grain sizes (Jessell, 1986;Urai, 1987).…”

Section: Introductionmentioning

confidence: 99%

“…This leads to the gradual transformation of low-angle dislocation walls into subgrain boundaries (Weikusat et al, 2017b) and eventually into new high-angle grain boundaries. This process of rotational recrystallization or polygonisation leads to a grain size reduction (Alley et al, 1995;Roessiger et al, 2011). The formation of new grains by spontaneous nucleation is a further mechanism of grain-size reduction, but is thought to be very unlikely in the absence of strong chemical driving forces, as is the case for ice (Drury and Urai, 1990;Humphreys and Hatherly, 2004;Faria et al, 2014b).…”

Section: Introductionmentioning

confidence: 99%

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The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

et al. 2017

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The flow of ice depends on the properties of the aggregate of individual ice crystals, such as grain size or lattice orientation distributions. Therefore, an understanding of the processes controlling ice micro-dynamics is needed to ultimately develop a physically based macroscopic ice flow law. We investigated the relevance of the process of grain dissection as a grain-size-modifying process in natural ice. For that purpose, we performed numerical multi-process microstructure modeling and analyzed microstructure and crystallographic orientation maps from natural deep ice-core samples from the North Greenland Eemian Ice Drilling (NEEM) project. Full crystallographic orientations measured by electron backscatter diffraction (EBSD) have been used together with c-axis orientations using an optical technique (Fabric Analyser). Grain dissection is a feature of strain-induced grain boundary migration. During grain dissection, grain boundaries bulge into a neighboring grain in an area of high dislocation energy and merge with the opposite grain boundary. This splits the high dislocation-energy grain into two parts, effectively decreasing the local grain size. Currently, grain size reduction in ice is thought to be achieved by either the progressive transformation from dislocation walls into new high-angle grain boundaries, called subgrain rotation or polygonisation, or bulging nucleation that is assisted by subgrain rotation. Both our time-resolved numerical modeling and NEEM ice core samples show that grain dissection is a common mechanism during ice deformation and can provide an efficient process to reduce grain sizes and counter-act dynamic grain-growth in addition to polygonisation or bulging nucleation. Thus, our results show that solely strain-induced boundary migration, in absence of subgrain rotation, can reduce grain sizes in polar ice, in particular if strain energy gradients are high. We describe the microstructural characteristics that can be used to identify grain dissection in natural microstructures.

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A general unified expression for solute and heat dispersion in homogeneous porous media

Bons

Blum

2013

Water Resour. Res.

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[1] Perturbations of temperature or solute concentration in a porous medium spread out by heat or molecular diffusion, respectively. If the pore-filling medium (e.g., water in soil) flows, this causes additional spreading of the perturbation due to the variation of local flow velocities and the tortuous flow lines through pore space. Together, this is termed dispersion, which plays an important role in geothermal energy production, contaminant transport, and reactor beds. Numerous models have been proposed to describe the dispersion coefficient as a function of flow rates, diffusion rates and other parameters, such as pore geometry. These models are either for heat (thermal) or solute dispersion, and often only valid for a limited range of flow rates, typically expressed in terms of the Peclet number. Here we present a single, universal expression for both the heat and solute dispersion coefficient in homogeneous porous media, valid over a wide range of Peclet numbers. Only three parameters have to be determined, which depend mainly on the pore geometry of the material. The expression facilitates the physical understanding of dispersion and may be helpful for the interpretation of numerical microscopic modeling results. It has the practical advantage that the heat dispersion coefficient can easily be calculated from the solute dispersion coefficient (or vice versa) and that dispersion coefficients over a wide range of Peclet numbers can be estimated from measurements over only a limited range.Citation: Bons, P. D., B. P. van Milligen, and P. Blum (2013), A general unified expression for solute and heat dispersion in homogeneous porous media, Water Resour. Res., 49,[6166][6167][6168][6169][6170][6171][6172][6173][6174][6175][6176][6177][6178]

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Competition between grain growth and grain-size reduction in polar ice

Cited by 27 publications

References 50 publications

Full-field predictions of ice dynamic recrystallisation under simple shear conditions

Full-field predictions of ice dynamic recrystallisation under simple shear conditions

The Relevance of Grain Dissection for Grain Size Reduction in Polar Ice: Insights from Numerical Models and Ice Core Microstructure Analysis

A general unified expression for solute and heat dispersion in homogeneous porous media

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