Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 2 the role of grain size and premelting on ice deformation at high homologous temperature

Abstract. The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine grained glacial ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser grained Eemian ice with a partial girdle type of CPO. In this study, the grain size sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine grained glacial layers are about an order of magnitude higher than in the much coarser grained Eemian layers. The dominant deformation mechanisms between the layers is also different with basal slip accommodated by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the glacial layers, while GBS-limited creep and dislocation creep (basal slip accommodated by non-basal slip) contribute both roughly equally to bulk strain in the coarse grained layers. Due to the large difference in microstructure between the impurity-rich glacial ice and the impurity-depleted Eemian ice at premelting temperatures (T>262 K), it is expected that the fine grained layers deform mainly by simple shear at high strain rates, while the coarse grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between glacial and interglacial ice at temperatures just below the melting point can have important consequences for ice dynamics close to the bedrock.

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Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 2: The role of grain size and premelting on ice deformation at high homologous temperature

The Cryosphere ◽

10.5194/tc-14-2449-2020 ◽

2020 ◽

Vol 14 (7) ◽

pp. 2449-2467 ◽

Cited By ~ 1

Author(s):

Ernst-Jan N. Kuiper ◽

Johannes H. P. de Bresser ◽

Martyn R. Drury ◽

Jan Eichler ◽

Gill M. Pennock ◽

...

Keyword(s):

Grain Size ◽

Basal Slip ◽

Ice Core ◽

Slip Rate ◽

Coarse Grained ◽

Strain Rates ◽

Fine Grained ◽

Composite Flow ◽

Flow Law ◽

Limited Creep

Abstract. The ice microstructure in the lower part of the North Greenland Eemian Ice Drilling (NEEM) ice core consists of relatively fine-grained ice with a single maximum crystallographic preferred orientation (CPO) alternated by much coarser-grained ice with a partial (great circle) girdle or multi-maxima CPO. In this study, the grain-size-sensitive (GSS) composite flow law of Goldsby and Kohlstedt (2001) was used to study the effects of grain size and premelting (liquid-like layer along the grain boundaries) on strain rate in the lower part of the NEEM ice core. The results show that the strain rates predicted in the fine-grained layers are about an order of magnitude higher than in the much coarser-grained layers. The dominant deformation mechanisms, based on the flow relation of Goldsby and Kohlstedt (2001), between the layers is also different, with basal slip rate limited by grain boundary sliding (GBS-limited creep) being the dominant deformation mechanism in the finer-grained layers, while GBS-limited creep and dislocation creep (basal slip rate limited by non-basal slip) contribute both roughly equally to bulk strain in the coarse-grained layers. Due to the large difference in microstructure between finer-grained ice and the coarse-grained ice at premelting temperatures (T>262 K), it is expected that the fine-grained layers deform at high strain rates, while the coarse-grained layers are relatively stagnant. The difference in microstructure, and consequently in viscosity, between impurity-rich and low-impurity ice can have important consequences for ice dynamics close to the bedrock.

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Using a composite flow law to model deformation in the NEEM deep ice core, Greenland: Part 1 the role of grain size and grain size distribution on the deformation of Holocene and glacial ice

10.5194/tc-2018-274 ◽

2019 ◽

Author(s):

Ernst-Jan N. Kuiper ◽

Ilka Weikusat ◽

Johannes H. P. de Bresser ◽

Daniela Jansen ◽

Gill M. Pennock ◽

...

Keyword(s):

Grain Size ◽

Strain Rate ◽

Rheological Model ◽

Basal Slip ◽

Ice Core ◽

Glacial Ice ◽

Micro Scale ◽

Fine Grained ◽

Composite Flow ◽

End Members

Abstract. The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end members: (i) the micro-scale constant stress model where each grain deforms by the same stress and (ii) the micro-scale constant strain rate model where each grain deforms by the same strain rate. The model results show that basal slip accommodated by grain boundary sliding produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep (basal slip accommodated by non-basal slip) hardly contributes to deformation. The difference in calculated strain rate between the two model end members is relatively small. The calculated strain rate in the fine grained glacial ice (1419–2207 m) varies strongly with depth and is about 4–5 times higher than in the coarser grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m of depth. The results from the rheological model and microstructures in the glacial ice indicate that fine grained layers in the glacial ice will act as internal preferential sliding zones in the Greenland ice sheet.

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Using a composite flow law to model deformation in the NEEM deep ice core, Greenland – Part 1: The role of grain size and grain size distribution on deformation of the upper 2207 m

The Cryosphere ◽

10.5194/tc-14-2429-2020 ◽

2020 ◽

Vol 14 (7) ◽

pp. 2429-2448 ◽

Cited By ~ 3

Author(s):

Ernst-Jan N. Kuiper ◽

Ilka Weikusat ◽

Johannes H. P. de Bresser ◽

Daniela Jansen ◽

Gill M. Pennock ◽

...

Keyword(s):

Grain Size ◽

Strain Rate ◽

Size Distribution ◽

Ice Core ◽

Dislocation Creep ◽

Glacial Ice ◽

Fine Grained ◽

Composite Flow ◽

Flow Law ◽

End Members

Abstract. The effect of grain size on strain rate of ice in the upper 2207 m in the North Greenland Eemian Ice Drilling (NEEM) deep ice core was investigated using a rheological model based on the composite flow law of Goldsby and Kohlstedt (1997, 2001). The grain size was described by both a mean grain size and a grain size distribution, which allowed the strain rate to be calculated using two different model end-members: (i) the microscale constant stress model where each grain deforms by the same stress and (ii) the microscale constant strain rate model where each grain deforms by the same strain rate. The model results predict that grain-size-sensitive flow produces almost all of the deformation in the upper 2207 m of the NEEM ice core, while dislocation creep hardly contributes to deformation. The difference in calculated strain rate between the two model end-members is relatively small. The predicted strain rate in the fine-grained Glacial ice (that is, ice deposited during the last Glacial maximum at depths of 1419 to 2207 m) varies strongly within this depth range and, furthermore, is about 4–5 times higher than in the coarser-grained Holocene ice (0–1419 m). Two peaks in strain rate are predicted at about 1980 and 2100 m depth. The prediction that grain-size-sensitive creep is the fastest process is inconsistent with the microstructures in the Holocene age ice, indicating that the rate of dislocation creep is underestimated in the model. The occurrence of recrystallization processes in the polar ice that did not occur in the experiments may account for this discrepancy. The prediction of the composite flow law model is consistent with microstructures in the Glacial ice, suggesting that fine-grained layers in the Glacial ice may act as internal preferential sliding zones in the Greenland ice sheet.

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Submarine lava deltas of the 2018 eruption of Kīlauea volcano

Bulletin of Volcanology ◽

10.1007/s00445-020-01424-1 ◽

2021 ◽

Vol 83 (4) ◽

Author(s):

S. Adam Soule ◽

Michael Zoeller ◽

Carolyn Parcheta

Keyword(s):

Grain Size ◽

Pore Pressure ◽

Mechanistic Model ◽

Large Fraction ◽

Volcanic Hazards ◽

Lava Flows ◽

Coarse Grained ◽

Fine Grained ◽

Fine Grain ◽

Delta Formation

AbstractHawaiian and other ocean island lava flows that reach the coastline can deposit significant volumes of lava in submarine deltas. The catastrophic collapse of these deltas represents one of the most significant, but least predictable, volcanic hazards at ocean islands. The volume of lava deposited below sea level in delta-forming eruptions and the mechanisms of delta construction and destruction are rarely documented. Here, we report on bathymetric surveys and ROV observations following the Kīlauea 2018 eruption that, along with a comparison to the deltas formed at Pu‘u ‘Ō‘ō over the past decade, provide new insight into delta formation. Bathymetric differencing reveals that the 2018 deltas contain more than half of the total volume of lava erupted. In addition, we find that the 2018 deltas are comprised largely of coarse-grained volcanic breccias and intact lava flows, which contrast with those at Pu‘u ‘Ō‘ō that contain a large fraction of fine-grained hyaloclastite. We attribute this difference to less efficient fragmentation of the 2018 ‘a‘ā flows leading to fragmentation by collapse rather than hydrovolcanic explosion. We suggest a mechanistic model where the characteristic grain size influences the form and stability of the delta with fine grain size deltas (Pu‘u ‘Ō‘ō) experiencing larger landslides with greater run-out supported by increased pore pressure and with coarse grain size deltas (Kīlauea 2018) experiencing smaller landslides that quickly stop as the pore pressure rapidly dissipates. This difference, if validated for other lava deltas, would provide a means to assess potential delta stability in future eruptions.

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Strain-Rate and Grain‒Size Effects in Ice

Journal of Glaciology ◽

10.1017/s0022143000008844 ◽

1987 ◽

Vol 33 (115) ◽

pp. 274-280 ◽

Cited By ~ 50

Author(s):

David M. Cole

Keyword(s):

Grain Size ◽

Strain Rate ◽

Transition Point ◽

Boundary Migration ◽

Peak Stress ◽

Strain Rates ◽

Thin Sections ◽

Fine Grained ◽

Lower Strain ◽

Polycrystalline Ice

AbstractThis paper presents and discusses the results of constant deformation-rate tests on laboratory-prepared polycrystalline ice. Strain-rates ranged from 10−7to 10−1s−1, grain–size ranged from 1.5 to 5.8 mm, and the test temperature was −5°C.At strain-rates between 10−7and 10−3s−1, the stress-strain-rate relationship followed a power law with an exponent ofn= 4.3 calculated without regard to grain-size. However, a reversal in the grain-size effect was observed: below a transition point near 4 × 10−6s−1the peak stress increased with increasing grain-size, while above the transition point the peak stress decreased with increasing grain-size. This latter trend persisted to the highest strain-rates observed. At strain-rates above 10−3s−1the peak stress became independent of strain-rate.The unusual trends exhibited at the lower strain-rates are attributed to the influence of the grain-size on the balance of the operative deformation mechanisms. Dynamic recrystallization appears to intervene in the case of the finer-grained material and serves to lower the peak stress. At comparable strain-rates, however, the large-grained material still experiences internal micro-fracturing, and thin sections reveal extensive deformation in the grain-boundary regions that is quite unlike the appearance of the strain-induced boundary migration characteristic of the fine-grained material.

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Deformation Size Effects Due to Specimen and Grain Size in Microbending

Journal of Manufacturing Science and Engineering ◽

10.1115/1.4000943 ◽

2010 ◽

Vol 132 (1) ◽

Cited By ~ 21

Author(s):

Sunal Ahmet Parasiz ◽

Reid VanBenthysen ◽

Brad L. Kinsey

Keyword(s):

Grain Size ◽

Sheet Thickness ◽

Specimen Size ◽

Coarse Grained ◽

Thick Sheet ◽

Hardness Profile ◽

Localized Deformation ◽

Fine Grained ◽

Deformation Distribution ◽

Deformation Area

Sheet metal forming often consists of bending processes in which gradients of deformation exists through the thickness of the workpiece in a localized deformation area. In microscale bending, these deformation gradients become much steeper, as the changes in the deformation occur over short distances (in the order of micrometers). In addition, with miniaturization, the number of grains that are present through the thickness decreases significantly. In this research, the effect of grain size and specimen size on the deformation distribution through the thickness of microbent sheet specimens was investigated via microhardness evaluations. It was found that the deformation distribution, i.e., hardness profile, is not affected significantly by the grain size when the sheet thickness is large (for 1.625 mm specimens) or by miniaturization of the specimen size when the grain size is fine. However, the deformation distribution of the coarse grained specimens deviates from the fine grained ones and from the 1.625 mm thick sheet specimens when the specimen size is miniaturized.

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Mechanical Properties of Dye 3 Greenland Deep Ice Cores

Annals of Glaciology ◽

10.3189/1984aog5-1-1-8 ◽

1984 ◽

Vol 5 ◽

pp. 1-8 ◽

Cited By ~ 1

Author(s):

Nobuhiko Azuma ◽

Akira Higashi

Keyword(s):

Mechanical Properties ◽

Grain Size ◽

Power Law ◽

Ice Core ◽

Ice Cores ◽

Uniaxial Stress ◽

Strain Rates ◽

Compression Tests ◽

Polycrystalline Ice ◽

Relationship Of

Uniaxial compression tests were carried out with specimens cut from several deep ice cores obtained at Dye 3, Greenland, in 1980 and 1981. The power law relationship of = Αση was obtained between the uniaxial strain-rate and the uniaxial stress σ. In a range of strain-rates between 10−8 and 10−7 s−1, the value of the power n for samples with strong single maximum fabric was approximately 4, significantly larger than the value of 3 which has been generally accepted from experiments using artificial polycrystalline ice. A work-hardening effect was found in the ice-core samples taken from a depth of 1900 m, which had a smaller grain size than the others. Recrystallization occurred when the temperature of the specimen was raised during the test and this ultimately caused the formation of the so-called diamond pattern ice fabric.

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Cavitation Behavior of Ultra-Fine Grained Ti-6Al-4V Alloy Produced by Equal-Channel Angular Pressing

Materials Science Forum ◽

10.4028/www.scientific.net/msf.551-552.621 ◽

2007 ◽

Vol 551-552 ◽

pp. 621-626

Author(s):

Young Gun Ko ◽

Yong Nam Kwon ◽

Jung Hwan Lee ◽

Dong Hyuk Shin ◽

Chong Soo Lee

Keyword(s):

Grain Size ◽

Strain Rate ◽

Equal Channel Angular Pressing ◽

Cavity Growth ◽

Rate Sensitivity ◽

Theoretical Models ◽

Coarse Grained ◽

Fine Grained ◽

Angular Pressing ◽

Cavitation Behavior

Cavitation behavior during superplastic flow of ultra-fine grained (UFG) Ti-6Al-4V alloy was established with the variation of grain size and misorientation. After imposing an effective strainup to 8 via equal-channel angular pressing (ECAP) at 873 K, alpha-phase grains were markedly refined from 11 μm to ≈ 0.3 μm, and misorientation angle was increased. Uniaxial-tension tests were conducted for initial coarse grained (CG) and two UFG alloys (ε = 4 and 8) at temperature of 973 K and strain rate of 10-4 s-1. Quantitative measurements of cavitation evidenced that both the average size and the area fraction of cavities significantly decreased with decreasing grain size and/or increasing misorientation. It was also found that, when compared to CG alloy, cavitation as well as diffused necking was less prevalent in UFG alloys, which was presumably due to the higher value of strain-rate sensitivity. Based on the several theoretical models describing the cavity growth behavior, the cavity growth mechanism in UFG alloys was suggested.

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Martensitic Transformations and Functional Stability in Ultra-Fine Grained NiTi Shape Memory Alloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.584-586.852 ◽

2008 ◽

Vol 584-586 ◽

pp. 852-857 ◽

Cited By ~ 18

Author(s):

Juri Burow ◽

Egor Prokofiev ◽

Christoph Somsen ◽

Jan Frenzel ◽

Ruslan Valiev ◽

...

Keyword(s):

Grain Size ◽

Shape Memory Alloys ◽

Shape Memory ◽

Thermomechanical Processing ◽

High Pressure Torsion ◽

Martensitic Transformations ◽

Coarse Grained ◽

Functional Stability ◽

Fine Grained ◽

Niti Shape Memory Alloys

Martensitic transformations in NiTi shape memory alloys (SMAs) strongly depend on the microstructure. In the present work, we investigate how martensitic transformations are affected by various types of ultra-fine grained (UFG) microstructures resulting from various processing routes. NiTi SMAs with UFG microstructures were obtained by equal channel angular pressing, high pressure torsion, wire drawing and subsequent annealing treatments. The resulting material states were characterized by transmission electron microscopy and differential scanning calorimetry (DSC). The three thermomechanical processing routes yield microstructures which significantly differ in terms of grain size and related DSC chart features. While the initial coarse grained material shows a well defined one-step martensitic transformation on cooling, two-step transformations were found for all UFG material states. The functional stability of the various UFG microstructures was evaluated by thermal cycling. It was found that UFG NiTi alloys show a significantly higher stability. In the present work, we also provide preliminary results on the effect of grain size on the undercooling required to transform the material into B19’ and on the related heat of transformation.

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Effect of Silver on Superplastic Deformation in YBa2Cu3O7–x/Ag Composites

Journal of Materials Research ◽

10.1557/jmr.2002.0173 ◽

2002 ◽

Vol 17 (5) ◽

pp. 1172-1177

Author(s):

Jondo Yun ◽

Ye T. Chou ◽

Martin P. Harmer

Keyword(s):

Activation Energy ◽

Grain Size ◽

Superplastic Deformation ◽

Close Agreement ◽

Silver Content ◽

Strain Rates ◽

Compression Tests ◽

Fine Grained ◽

Soft Inclusion ◽

Activation Energy Of Deformation

Superplastic deformation was studied in fine-grained (0.7–1.1 μm) YBa2Cu3O7–x/Ag composites containing 2.5–25 vol% Ag. The compression tests were conducted in the temperature range of 750–875 °C and at strain rates of 10−5 to 10−3/s. For the YBa2Cu3O7−x/25%Ag composites with grain size of 0.7–1.1 μm, deformed at 800–850 °C and 10−5 to 10−3/s, the stress exponent, grain size exponent, and the activation energy of deformation were 2.0 ± 0.1, 2.5 ± 0.7, and 760 ± 100 kJ/mol, respectively. These values were the same as those of the pure YBa2Cu3O7−x, indicating that the deformation of the composite was controlled by that of the rigid YBa2Cu3O7−x phase. However, the strain rate was increased by the addition of silver as explained by the soft inclusion model of Chen. The dependence of the flow stress on the silver content was in close agreement with the prediction of the model.

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