scholarly journals The temperature change shortcut: effects of mid-experiment temperature changes on the deformation of polycrystalline ice

2020 ◽  
Author(s):  
Lisa Craw ◽  
Adam Treverrow ◽  
Sheng Fan ◽  
Mark Peternell ◽  
Sue Cook ◽  
...  
Keyword(s):  
Strain Rate ◽  
Temperature Change ◽  
Constant Temperature ◽  
Ice Sheets ◽  
Strain Rates ◽  
Temperature Step ◽  
Ice Shelves ◽  
Polycrystalline Ice ◽  
Long Time ◽  
Run Time

Abstract. It is vital to understand the mechanical properties of flowing ice to model the dynamics of ice sheets and ice shelves, and to predict their behaviour in the future. We can do this by performing deformation experiments on ice in laboratories, and examining its mechanical and microstructural responses. However, natural conditions in ice sheets and ice shelves extend to low temperatures ( 0.08), and emulating these conditions in laboratory experiments can take an impractically long time. It is possible to accelerate an experiment by running it at a higher temperature in the early stages, and then lowering the temperature to meet the target conditions once the tertiary creep stage is reached. This can reduce total experiment run-time by > 1000 hours, however it is not known if this could affect the final strain rate or microstructure of the ice and potentially introduce a bias into the data. We deformed polycrystalline ice samples in uniaxial compression at −2 °C before lowering the temperature to either −7 °C or −10 °C, and compared the results to constant temperature experiments. Tertiary strain rates adjusted to the change in temperature very quickly (within 3 % of the total experiment run-time), with no significant deviation from strain rates measured in constant-temperature experiments. In experiments with a smaller temperature step (−2 °C to −7 °C) there is no observable difference in the final microstructure between changing-temperature and constant-temperature experiments which could introduce a bias into experimental results. For experiments with a larger temperature step (−2 °C to −10 °C), there are quantifiable differences in the microstructure. These differences are related to different recrystallisation mechanisms active at −10 °C, which are not as active when the first stages of the experiment are performed at −2 °C. For studies in which the main aim is obtaining tertiary strain rate data, we propose that a mid-experiment temperature change is a viable method for reducing the time taken to run low stress and low temperature experiments in the laboratory.

scholarly journals The temperature change shortcut: effects of mid-experiment temperature changes on the deformation of polycrystalline ice

2021 ◽  
Vol 15 (5) ◽  
pp. 2235-2250
Author(s):  
Lisa Craw ◽  
Adam Treverrow ◽  
Sheng Fan ◽  
Mark Peternell ◽  
Sue Cook ◽  
...  
Keyword(s):  
Strain Rate ◽  
Temperature Change ◽  
Constant Temperature ◽  
Ice Sheets ◽  
Strain Rates ◽  
Temperature Step ◽  
Ice Shelves ◽  
Polycrystalline Ice ◽  
Long Time ◽  
Run Time

Abstract. It is vital to understand the mechanical properties of flowing ice to model the dynamics of ice sheets and ice shelves and to predict their behaviour in the future. We can increase our understanding of ice physical properties by performing deformation experiments on ice in laboratories and examining its mechanical and microstructural responses. However, natural conditions in ice sheets and ice shelves extend to low temperatures (≪-10 ∘C), and high octahedral strains (> 0.08), and emulating these conditions in laboratory experiments can take an impractically long time. It is possible to accelerate an experiment by running it at a higher temperature in the early stages and then lowering the temperature to meet the target conditions once the tertiary creep stage is reached. This can reduce total experiment run-time by > 1000 h; however it is not known whether this could affect the final strain rate or microstructure of the ice and potentially introduce a bias into the data. We deformed polycrystalline ice samples in uniaxial compression at −2 ∘C before lowering the temperature to either −7 or −10 ∘C, and we compared the results to constant-temperature experiments. Tertiary strain rates adjusted to the change in temperature very quickly (within 3 % of the total experiment run-time), with no significant deviation from strain rates measured in constant-temperature experiments. In experiments with a smaller temperature step (−2 to −7 ∘C) there is no observable difference in the final microstructure between changing-temperature and constant-temperature experiments which could introduce a bias into experimental results. For experiments with a larger temperature step (−2 to −10 ∘C), there are quantifiable differences in the microstructure. These differences are related to different recrystallisation mechanisms active at −10 ∘C, which are not as active when the first stages of the experiment are performed at −2 ∘C. For studies in which the main aim is obtaining tertiary strain rate data, we propose that a mid-experiment temperature change is a viable method for reducing the time taken to run low-stress and low-temperature experiments in the laboratory.

scholarly journals Bubble Coalescence in Ice as a Tool for the Study of its Deformation History

1968 ◽  
Vol 7 (50) ◽  
pp. 155-159 ◽  
Author(s):  
J. Weertman
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Ice Sheets ◽  
Temperature Gradients ◽  
Bubble Coalescence ◽  
Bottom Surface ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
Deformation History ◽  
Ice Shelves

An analysis is made of the rate of bubble coalescence in an ice mass that is deforming. A total strain of at least 8 is required before appreciable coalescence occurs. The analysis has been applied to deforming ice shelves and ice sheets. No appreciable coalescence is expected in ice shelves but coalescence should occur in ice sheets (or glaciers) if the shear strain-rate at the bottom surface is of the order of 0·075/year or larger. Measurements of bubble concentration are capable of setting limits on paleo-strain-rates of the present ice sheets. Bubble migration down temperature gradients presents complications to the study of bubble coalescence.

scholarly journals Bubble Coalescence in Ice as a Tool for the Study of its Deformation History

1968 ◽  
Vol 7 (50) ◽  
pp. 155-159
Author(s):  
J. Weertman
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Ice Sheets ◽  
Temperature Gradients ◽  
Bubble Coalescence ◽  
Bottom Surface ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
Deformation History ◽  
Ice Shelves

An analysis is made of the rate of bubble coalescence in an ice mass that is deforming. A total strain of at least 8 is required before appreciable coalescence occurs. The analysis has been applied to deforming ice shelves and ice sheets. No appreciable coalescence is expected in ice shelves but coalescence should occur in ice sheets (or glaciers) if the shear strain-rate at the bottom surface is of the order of 0·075/year or larger. Measurements of bubble concentration are capable of setting limits on paleo-strain-rates of the present ice sheets. Bubble migration down temperature gradients presents complications to the study of bubble coalescence.

scholarly journals Strain-Rate and Grain‒Size Effects in Ice

1987 ◽  
Vol 33 (115) ◽  
pp. 274-280 ◽  
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.

Deformation of ice under high internal shear stresses

1969 ◽  
Vol 6 (4) ◽  
pp. 963-968 ◽  
Author(s):  
John J. Jonas ◽  
Fritz Müller
Keyword(s):  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Polarized Light ◽  
Shear Stresses ◽  
Strain Rates ◽  
Transparent Plastic ◽  
Cross Section Area ◽  
Section Area ◽  
Polycrystalline Ice ◽  
Glacier Surges

By means of transparent plastic dies, cylindrical samples of single crystal and polycrystalline ice were extruded into rods of one quarter the original cross-section area. The deformation was carried out at −5 °C and a mean strain rate of about 10−2 s−1. With the aid of polarized light, the formation of cracks and the occurrence of dynamic recrystallization were studied. The experiments of Steinemann, and more recent results in metals suggest that, during such plastic flow, two types of dynamic recrystallization are involved. At low strain rates, the recrystallization is periodic, leading to rapid increases in strain rate at constant applied stress; at higher strain rates, the recrystallization is continuous and the strain rate is constant. The possibility that dynamic recrystallization of the periodic type is associated with glacier surges is discussed.

scholarly journals Strain-Rate and Grain‒Size Effects in Ice

1987 ◽  
Vol 33 (115) ◽  
pp. 274-280 ◽  
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 10−7 to 10−1s−1, grain–size ranged from 1.5 to 5.8 mm, and the test temperature was −5°C.At strain-rates between 10−7 and 10−3 s−1, the stress-strain-rate relationship followed a power law with an exponent of n = 4.3 calculated without regard to grain-size. However, a reversal in the grain-size effect was observed: below a transition point near 4 × 10−6 s−1 the 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 10−3 s−1 the 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.

scholarly journals Relating the occurrence of crevasses to surface strain rates

1993 ◽  
Vol 39 (132) ◽  
pp. 255-266 ◽  
Author(s):  
David G. Vaughan
Keyword(s):  
Tensile Strength ◽  
Strain Rate ◽  
Impurity Content ◽  
Surface Strain ◽  
Strain Rates ◽  
Principal Stresses ◽  
Ice Dynamics ◽  
Ice Shelves ◽  
Creep Flow ◽  
Failure Envelopes

AbstractThe presence of crevasses on the surface of ice masses indicates that a fracture criterion has been met. Understanding how crevasses form will provide information about the stress and strain-rate fields in the ice. This study derives a relationship between measurements of strain rate and observations of crevassing on the surface of ice masses. A literature search yielded 17 polar and alpine locations where strain rates had been measured and crevassing recorded. By plotting strain rates (converted to stresses using a creep law) using axes representing the surface-parallel principal stresses, failure envelopes were derived by enclosing measurements where surface crevassing was absent. The derived failure envelopes were found to conform well to theoretical ones predicted by the Coulomb and the maximum octahedral shear stress (von Mises) theories of failure. The derived failure envelopes were scaled by the tensile strength, which was found to vary from 90 to 320 kPa. There was no systematic variation of tensile strength with either temperature at 10 m depth or the method used to locate the crevasses. The observed variation in tensile strength could result from variations in ice properties (e.g. crystal size, impurity content or density) or could be related to uncertainty in the constitutive relation. Creep flow and fracture share a very similar temperature dependence, suggesting similar crystal-scale processes are responsible for both. The observed relationship will provide a supplementary tool with which to verify and test models of ice dynamics against remotely sensed imagery. The study also indicates that a temperature rise of a few degrees throughout the ice column will not result directly in any increase in calving rates from the large Antarctic ice shelves such as the Filchner–Ronne or Ross Ice Shelves.

Grain Size and the Compressive Strength of Ice

1985 ◽  
Vol 107 (3) ◽  
pp. 369-374 ◽  
Author(s):  
D. M. Cole
Keyword(s):  
Grain Size ◽  
Size Effect ◽  
Strain Rate ◽  
Peak Stress ◽  
Applied Strain ◽  
Test Material ◽  
Strain Rates ◽  
Grain Size Effect ◽  
Compression Tests ◽  
Polycrystalline Ice

This work presents the results of uniaxial compression tests on freshwater polycrystalline ice. Grain size of the test material ranged from 1.5 to 5 mm, strain rate ranged from 10−6 to 10−2 s−1 and the temperature was −5°C. The grain size effect emerged clearly as the strain rate increased to 10−5 s−1 and persisted to the highest applied strain rates. On average, the stated increase in grain size brought about a decrease in peak stress of approximately 31 percent. The occurrence of the grain size effect coincided with the onset of visible cracking. The strength of the material increased to a maximum at a strain rate of 10−3 s−1, and then dropped somewhat as the strain rate increased further to 10−2 s−1. Strain at peak stress generally tended to decrease with both increasing grain size and increasing strain rate. The results are discussed in terms of the deformational mechanisms which lead to the observed behavior.

scholarly journals The effects of Ca++ on the strength of polycrystalline ice

2016 ◽  
Vol 62 (235) ◽  
pp. 954-962 ◽  
Author(s):  
KEVIN HAMMONDS ◽  
IAN BAKER
Keyword(s):  
Strain Rate ◽  
Microstructural Analysis ◽  
Constant Load ◽  
Applied Strain ◽  
Strain Rates ◽  
Compression Tests ◽  
Polycrystalline Ice ◽  
Post Test ◽  
The Mean ◽  
Deformation Tests

ABSTRACTRecent studies have suggested a physical link between Ca++ ions and an increase in the ductility or ‘softening’ of polycrystalline ice. In order to investigate the potential effects of Ca++ on deformation, we created sets of both undoped and CaSO4-doped specimens of polycrystalline ice for testing in uniaxial tension or compression. Deformation tests in tension were carried out under a constant load at an initial stress of 0.75 MPa and a temperature of −6°C. Compression tests were carried out at −10 and −20°C at constant strain rates of 1×10−4 s−1, 1 × 10−5 s−1 and 1 × 10−6 s−1 and taken to 5% strain. Our results show that CaSO4 increases the strength of polycrystalline ice at higher strain rates and lower temperatures, an effect that decreases with decreasing strain rate and higher temperatures. A microstructural analysis of the post-test compression specimens reveals mean grain diameters much larger in the CaSO4-doped specimens tested at the lowest applied strain rate of 1 × 10−6 s−1. Precipitates were found to have formed along grain boundaries in some doped specimens and evidence of intergranular fracture was observed in all specimens tested at 1 × 10−4 and 1 × 10−5 s−1. In tension-tested specimens, there was no difference in the mean grain diameter between doped and undoped specimens at 25% strain.

scholarly journals The Confined Compressive Strength of Polycrystalline Ice

1982 ◽  
Vol 28 (98) ◽  
pp. 171-178 ◽  
Author(s):  
Stephen J. Jones
Keyword(s):  
Compressive Strength ◽  
Strain Rate ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Strain Rates ◽  
Maximum Compressive Stress ◽  
A Value ◽  
Polycrystalline Ice ◽  
Confining Pressures ◽  
Unconfined Strength

AbstractTriaxial tests were carried out on randomly oriented, laboratory-made, polycrystalline ice, between strain-rates of 10–7 and 10–1 s–1 and with confining pressures from 0.1 to 85 MN m–2, at –11 ± 1°C. Below strain-rates of about 10–5 s–1 the confining pressure has little effect, but at higher strain-rates the confining pressure prevents cracking which allows the compressive strength to rise to a value greater than the unconfined compressive strength. At 1.4 ×10–2 s–1, the unconfined strength of 12 MN m–2 rises to 26 MN m–2 with a confining pressure of 25 MN m–2, before dropping slowly with greater confining pressures. Above 10–2 s–1 the unconfined strength decreases rapidly with increasing strain-rate, but the confined strength continues to increase. The dependence of strain rate on the maximum compressive stress is discussed.

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