Recrystallization processes, microstructure and crystallographic preferred orientation evolution in polycrystalline ice during high-temperature simple shear

Journaux, Baptiste; Chauve, Thomas; Montagnat, Mâurine; Tommasi, Andréa; Barou, Fabrice; Mainprice, David; Gest, Léa

doi:10.5194/tc-13-1495-2019

Cited by 29 publications

(63 citation statements)

References 72 publications

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“…These interpretations are consistent with those in microstructural studies of experimentally deformed ice at high temperatures (e.g. Kamb, 1972;Montagnat et al, 2015;Vaughan et al, 2017;Journaux et al, 2019), and natural ice samples deformed at relatively high temperature (Duval and Castelnau, 1995). 350 6.2 Composite sections c-axis patterns for individual samples appear to represent typical multimaxima CPO patterns of the kind that have previously been identified in warm, coarse-grained ice (Fig.…”

Section: Composites 310supporting

confidence: 87%

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Electron backscatter diffraction (EBSD) based determination of crystallographic preferred orientation (CPO) in warm, coarse-grained ice: a case study, Storglaciären, Sweden

Monz

Hudleston

Prior

et al. 2020

Preprint

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Abstract. Microstructures provide key insights into understanding the mechanical behavior of ice. Crystallographic preferred orientation (CPO) develops during plastic deformation as ice dynamically recrystallizes, with the dominance of intracrystalline glide on the basal plane. CPO patterns in fine-grained ice have been relatively well characterized and understood in experiments and nature, whereas CPO patterns in "warm" (T > −10 ºC), coarse-grained, natural ice remain enigmatic. Previous microstructural studies of coarse-grained ice have been limited to c-axis orientations using light optical measurements. We have developed a new sample preparation technique, by constructing composite sections, to allow us to use electron backscatter diffraction (EBSD) to obtain a representative, bulk CPO on coarse-grained ice. We suggest that a grain sampling bias of large, branching crystals that appear multiple times as island grains in thin section may result in the typical multiple maxima CPOs previously identified in warm, coarse-grained ice that has been subjected to prolonged shear. CPOs combined from multiple samples of highly sheared ice from Storglaciären provide a more comprehensive picture of the microstructure and yield a pronounced cluster of c-axes sub-normal to the shear plane and elongate or split in a plane normal to the shear direction, and a concomitant girdle of a-axes parallel to the shear plane with a maximum perpendicular to the shear direction. This pattern compares well with patterns produced by sub-sampling data sets from experimentally sheared ice at high homologous temperatures up to strains of ~ 1.5. Shear strains in the margin of Storglaciären are much higher than those in experimental work. At much lower natural strain rates, dynamic recrystallization, particularly grain boundary migration, may have been more effective so that the CPO has been continuously reset and represents a smaller, final fraction of the shear history, rather than the entire finite strain history.

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Section: Composites 310supporting

confidence: 87%

“…1d; e.g. Duval, 1981;Bouchez and Duval 1982;Budd and Jacka, 1989;Budd et al, 2013;Qi et al, 2019;Journaux et al, 2019). This dual maxima pattern of CPO development under simple shear has been described in nature (Hudleston, 1977a;Jackson and Kamb, 1997).…”

mentioning

confidence: 84%

Electron backscatter diffraction (EBSD) based determination of crystallographic preferred orientation (CPO) in warm, coarse-grained ice: a case study, Storglaciären, Sweden

Monz

Hudleston

Prior

et al. 2020

Preprint

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“…Following Cuffey and Paterson (2010), we argue that the existence of multi-maxima fabrics is the result of combined compressional (σ xx ) and shear stresses (τ xz ). This hypothesis is also supported by microdynamical models (Llorens et al, 2016) and laboratory investigations (Journaux et al, 2019). These investigations provide evidence that simple shear processes in temperate ice produce two maxima, one perpendicular to the shear plane (parallel to the normal vector of that plane) and a second maximum in the direction of shearing.…”

Section: Discussionsupporting

confidence: 52%

“…the horizontal margin (τ zx ) would vanish over time as the crystals tend to rotate towards the maximum perpendicular to the actual shear plane (Duval, 1981;Llorens et al, 2016;Journaux et al, 2019) and emphasise the vertical maximum (τ xz ). The fact that both maxima (τ xz and τ zx ) are still visible, fits again to the assumption of a continuous recrystallisation process and relatively young but fast growing ice grains.…”

Section: Discussionmentioning

confidence: 99%

Crystallographic analysis of temperate ice on Rhonegletscher, Swiss Alps

Hellmann¹,

Kerch²,

Weikusat³

et al. 2020

Preprint

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Abstract. The crystal orientation fabric (COF) was studied at an ice core that was obtained from the temperate Rhonegletscher, located in the Central Swiss Alps. Seven samples, extracted at depths between 2 and 79 m, were analysed with an automatic fabric analyser. The COF analysis revealed conspicuous four-maxima patterns of the c-axis orientations at all depths. Additional data, such as microstructural images, produced during the ice sample preparation process, were considered to interpret these patterns. Furthermore, repeated high-precision Global Navigation Satellite System (GNSS) surveying allowed the local glacier flow direction to be determined. The relative movements of the individual surveying points indicated horizontal compressive stresses parallel to the glacier flow. Finally, numerical modelling of the ice flow permitted to estimate the local stress distribution. An integrated analysis of all the data sets provided an explanation for the observed four-maximum patterns in the COF. The average azimuths and colatitudes of the c-axes of the individual core samples align with the compressive stress directions obtained from numerical modelling. The clustering of the c-axes in four maxima surrounding the predominant compressive stress direction is most likely the result of a fast migration recrystallisation in combination with the presence of significant shear stresses. This interpretation is supported by air bubble analysis of the LASM images. Our results indicate that COF studies, which were so far predominantly performed at cold ice samples from the polar regions, can also provide valuable insights on the stress and strain distribution within temperate glaciers.

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“…However, we have to re-evaluate the detail of this idea, as recent studies on deformed ice samples show there is no systematic relation between orientation and strain localization at low strain (Grennerat et al, 2012). Furthermore, studies of high-strain shear samples find no clear difference in the geometrically necessary dislocation density within the two maxima that develop in simple shear (Journaux et al, 2019). An alternative, and as yet incomplete, explanation from Kamb (1959) relates recrystallization directly to the elastic anisotropy of crystals and through this to the orientation of the stress field.…”

Section: Cpo Developmentmentioning

confidence: 95%

Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30 °C

et al. 2020

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Abstract. In order to better understand ice deformation mechanisms, we document the microstructural evolution of ice with increasing strain. We include data from experiments at relatively low temperatures (−20 and −30 ∘C), where the microstructural evolution with axial strain has never before been documented. Polycrystalline pure water ice was deformed under a constant displacement rate (strain rate ∼1.0×10-5 s−1) to progressively higher strains (∼ 3 %, 5 %, 8 %, 12 % and 20 %) at temperatures of −10, −20 and −30 ∘C. Microstructural data were generated from cryogenic electron backscattered diffraction (cryo-EBSD) analyses. All deformed samples contain subgrain (low-angle misorientations) structures with misorientation axes that lie dominantly in the basal plane, suggesting the activity of dislocation creep (glide primarily on the basal plane), recovery and subgrain rotation. Grain boundaries are lobate in all experiments, suggesting the operation of strain-induced grain boundary migration (GBM). Deformed ice samples are characterized by interlocking big and small grains and are, on average, finer grained than undeformed samples. Misorientation analyses between nearby grains in 2-D EBSD maps are consistent with some 2-D grains being different limbs of the same irregular grain in the 3-D volume. The proportion of repeated (i.e. interconnected) grains is greater in the higher-temperature experiments suggesting that grains have more irregular shapes, probably because GBM is more widespread at higher temperatures. The number of grains per unit area (accounting for multiple occurrences of the same 3-D grain) is higher in deformed samples than undeformed samples, and it increases with strain, suggesting that nucleation is involved in recrystallization. “Core-and-mantle” structures (rings of small grains surrounding big grains) occur in −20 and −30 ∘C experiments, suggesting that subgrain rotation recrystallization is active. At temperatures warmer than −20 ∘C, c axes develop a crystallographic preferred orientation (CPO) characterized by a cone (i.e. small circle) around the compression axis. We suggest the c-axis cone forms via the selective growth of grains in easy slip orientations (i.e. ∼ 45∘ to shortening direction) by GBM. The opening angle of the c-axis cone decreases with strain, suggesting strain-induced GBM is balanced by grain rotation. Furthermore, the opening angle of the c-axis cone decreases with temperature. At −30 ∘C, the c-axis CPO changes from a narrow cone to a cluster, parallel to compression, with increasing strain. This closure of the c-axis cone is interpreted as the result of a more active grain rotation together with a less effective GBM. We suggest that lattice rotation, facilitated by intracrystalline dislocation glide on the basal plane, is the dominant mechanism controlling grain rotation. Low-angle neighbour-pair misorientations, relating to subgrain boundaries, are more extensive and extend to higher misorientation angles at lower temperatures and higher strains supporting a relative increase in the importance of dislocation activity. As the temperature decreases, the overall CPO intensity decreases, primarily because the CPO of small grains is weaker. High-angle grain boundaries between small grains have misorientation axes that have distributed crystallographic orientations. This implies that, in contrast to subgrain boundaries, grain boundary misorientation is not controlled by crystallography. Nucleation during recrystallization cannot be explained by subgrain rotation recrystallization alone. Grain boundary sliding of finer grains or a different nucleation mechanism that generates grains with random orientations could explain the weaker CPO of the fine-grained fraction and the lack of crystallographic control on high-angle grain boundaries.

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Recrystallization processes, microstructure and crystallographic preferred orientation evolution in polycrystalline ice during high-temperature simple shear

Cited by 29 publications

References 72 publications

Electron backscatter diffraction (EBSD) based determination of crystallographic preferred orientation (CPO) in warm, coarse-grained ice: a case study, Storglaciären, Sweden

Electron backscatter diffraction (EBSD) based determination of crystallographic preferred orientation (CPO) in warm, coarse-grained ice: a case study, Storglaciären, Sweden

Crystallographic analysis of temperate ice on Rhonegletscher, Swiss Alps

Temperature and strain controls on ice deformation mechanisms: insights from the microstructures of samples deformed to progressively higher strains at −10, −20 and −30 °C

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