scholarly journals Ice deformed in compression and simple shear: control of temperature and initial fabric

2012 ◽  
Vol 58 (207) ◽  
pp. 11-22 ◽  
Author(s):  
Christopher J.L. Wilson ◽  
Mark Peternell
Keyword(s):  
Shear Strain ◽  
Simple Shear ◽  
Critical Role ◽  
Shear Zones ◽  
Preferred Orientation ◽  
Shear Strain Rate ◽  
Compression Strain ◽  
Mechanical Evolution ◽  
Polycrystalline Ice ◽  
Strain Magnitude

AbstractLayered and polycrystalline ice was experimentally deformed in general shear involving axial compression (strain magnitude 0.5-17%) and simple shear (strain magnitude γ = 0.1-1.4). As the temperature is increased from -20°C to -2°C, there is at least a twofold enhancement in octahedral shear strain rate, which coincides with the onset of extensive dynamic recrystallization and a change in grain-size distribution at -15°C. Between -150C and -10°C the c-axis preferred orientation rapidly evolves with the initiation of two-maxima fabrics in shear zones. From -10°C to -2°C there is progressive evolution of a final c-axis pattern that is asymmetric with respect to the direction of shortening, with a strong maximum at ~5° to the pole of the shear zone, a sense of asymmetry in the direction of the shear, and a secondary maximum inclined at ~45° to the plane of shearing. An initial c-axis preferred orientation plays a critical role in the initial mechanical evolution. In contrast to established ideas, a strong alignment of basal planes parallel to the plane of easy glide inhibited deformation and there was an increased component of strain hardening until recrystallization processes become dominant.

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

2019 ◽  
Vol 13 (5) ◽  
pp. 1495-1511 ◽  
Author(s):  
Baptiste Journaux ◽  
Thomas Chauve ◽  
Maurine Montagnat ◽  
Andrea Tommasi ◽  
Fabrice Barou ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Grain Boundaries ◽  
Simple Shear ◽  
Shear Plane ◽  
Preferred Orientation ◽  
Dislocation Slip ◽  
Crystallographic Preferred Orientation ◽  
Polycrystalline Ice

Abstract. Torsion experiments were performed in polycrystalline ice at high temperature (0.97 Tm) to reproduce the simple shear kinematics that are believed to dominate in ice streams and at the base of fast-flowing glaciers. As clearly documented more than 30 years ago, under simple shear ice develops a two-maxima c axis crystallographic preferred orientation (CPO), which evolves rapidly into a single cluster CPO with a c axis perpendicular to the shear plane. Dynamic recrystallization mechanisms that occur in both laboratory conditions and naturally deformed ice are likely candidates to explain the observed CPO evolution. In this study, we use electron backscatter diffraction (EBSD) and automatic ice texture analyzer (AITA) to characterize the mechanisms accommodating deformation, the stress and strain heterogeneities that form under torsion of an initially isotropic polycrystalline ice sample at high temperature, and the role of dynamic recrystallization in accommodating these heterogeneities. These analyses highlight an interlocking microstructure, which results from heterogeneity-driven serrated grain boundary migration, and sub-grain boundaries composed of dislocations with a [c]-component Burgers vector, indicating that strong local stress heterogeneity develops, in particular, close to grain boundaries, even at high temperature and high finite shear strain. Based on these observations, we propose that nucleation by bulging, assisted by sub-grain boundary formation and followed by grain growth, is a very likely candidate to explain the progressive disappearance of the c axis CPO cluster at low angle to the shear plane and the stability of the one normal to it. We therefore strongly support the development of new polycrystal plasticity models limiting dislocation slip on non-basal slip systems and allowing for efficient accommodation of strain incompatibilities by an association of bulging and formation of sub-grain boundaries with a significant [c] component.

scholarly journals Deformation rates in combined compression and shear for ice which is initially isotropic and after the development of strong anisotropy

1996 ◽  
Vol 23 ◽  
pp. 247-252 ◽  
Author(s):  
Li Jun ◽  
T.H Jacka ◽  
W.F. Budd
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Stress State ◽  
Strain Rate ◽  
Shear Strain ◽  
Uniaxial Compression ◽  
Simple Shear ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
State Dependent

Laboratory-prepared fine-grained, initially isotropic polycrystalline ice samples were deformed under conditions of simple shear with simultaneous uniaxial compression at a constant temperature of −2.0°C. The aim was to investigate the effects of stress configuration on the flow rate of initially isotropic ice and on ice with subsequent stress and strain-induced anisotropy. Experiments were carried out for various combinations of shear and compression with shear stress ranging from 0 to 0.49 MPa and compressive stress ranging from 0 to 0.98 MPa, but such that for every experiment the octahedral shear stress was 0.4 MPa.The strain curves resulting from the experiments clearly exhibit minimum strain rates while the ice is still isotropic, and steady-state tertiary strain rates along with the development of steady-state anisotropic fabric patterns. With constant octahedral stress (root-mean-square of the principal stress deviators), the minimum octahedral shear-strain rate has no dependence on stress configuration. This result supports the hypothesis that the flow of isotropic ice is dependent only on the second invariant of the stress tensor. This fundamental assumption has been used to provide a general description of ice-flow behaviour independent of the stress configuration (e.g. Nye, 1953; Glen, 1958; Budd, 1969).For the tertiary flow of anisotropic ice, the octahedral strain rate is stress-state dependent as a consequence of the developed crystal-orientation fabric, which is also stress-state dependent, and which develops with strain and rotation. The present tests indicate that the enhancement factor for steady-state tertiary octahedral shear-strain rate depends on the shear or compression fraction and varies from about 10 for simple shear (with zero compression) to about 3 for uniaxial compression (with zero shear).

scholarly journals Flow Behavior of Basal Ice as Related to Modeling Considerations

1984 ◽  
Vol 5 ◽  
pp. 141-148 ◽  
Author(s):  
Hitoshi Shoji ◽  
Chester C. Langway
Keyword(s):  
Shear Strain ◽  
Simple Shear ◽  
Flow Behavior ◽  
Ice Core ◽  
Ice Sheet ◽  
Strain Rates ◽  
Basal Ice ◽  
Polycrystalline Ice ◽  
Ice Sheet Modeling ◽  
Using Data

Simple shear tests on the bottom 17 m of basal ice from Camp Century, Greenland, were carried out in order to study the flow behavior near the bottom of an ice sheet and its implications for ice-sheet modeling. The ice core was recovered in 1966. Our experimental results show that the basal ice tested, (which contained alternating bands of dirty and clean ice) has the highest strain-rate ever reported for polycrystalline ice under simple shear. The enhancement factors obtained are interpreted in terms of fabric, ageing, and impurity. Horizontal velocity profiles are calculated using data reported previously for Camp Century and Dye 3 stations. Various depth-age relationships are compared with these data. The higher than expected shear strain-rates measured on samples of near-bottom ice from Camp Century may very well exist at other locations. If such high shear strain-rates are more prevalent than presently thought, they could have an important bearing on ages calculated by physical or mathematical models of ice sheets.

scholarly journals Flow Behavior of Basal Ice as Related to Modeling Considerations

1984 ◽  
Vol 5 ◽  
pp. 141-148 ◽  
Author(s):  
Hitoshi Shoji ◽  
Chester C. Langway
Keyword(s):  
Shear Strain ◽  
Simple Shear ◽  
Flow Behavior ◽  
Ice Core ◽  
Ice Sheet ◽  
Strain Rates ◽  
Basal Ice ◽  
Polycrystalline Ice ◽  
Ice Sheet Modeling ◽  
Using Data

Simple shear tests on the bottom 17 m of basal ice from Camp Century, Greenland, were carried out in order to study the flow behavior near the bottom of an ice sheet and its implications for ice-sheet modeling. The ice core was recovered in 1966. Our experimental results show that the basal ice tested, (which contained alternating bands of dirty and clean ice) has the highest strain-rate ever reported for polycrystalline ice under simple shear. The enhancement factors obtained are interpreted in terms of fabric, ageing, and impurity. Horizontal velocity profiles are calculated using data reported previously for Camp Century and Dye 3 stations. Various depth-age relationships are compared with these data. The higher than expected shear strain-rates measured on samples of near-bottom ice from Camp Century may very well exist at other locations. If such high shear strain-rates are more prevalent than presently thought, they could have an important bearing on ages calculated by physical or mathematical models of ice sheets.

scholarly journals Deformation rates in combined compression and shear for ice which is initially isotropic and after the development of strong anisotropy

1996 ◽  
Vol 23 ◽  
pp. 247-252 ◽  
Author(s):  
Li Jun ◽  
T.H Jacka ◽  
W.F. Budd
Keyword(s):  
Shear Stress ◽  
Steady State ◽  
Stress State ◽  
Strain Rate ◽  
Shear Strain ◽  
Uniaxial Compression ◽  
Simple Shear ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
State Dependent

Laboratory-prepared fine-grained, initially isotropic polycrystalline ice samples were deformed under conditions of simple shear with simultaneous uniaxial compression at a constant temperature of −2.0°C. The aim was to investigate the effects of stress configuration on the flow rate of initially isotropic ice and on ice with subsequent stress and strain-induced anisotropy. Experiments were carried out for various combinations of shear and compression with shear stress ranging from 0 to 0.49 MPa and compressive stress ranging from 0 to 0.98 MPa, but such that for every experiment the octahedral shear stress was 0.4 MPa. The strain curves resulting from the experiments clearly exhibit minimum strain rates while the ice is still isotropic, and steady-state tertiary strain rates along with the development of steady-state anisotropic fabric patterns. With constant octahedral stress (root-mean-square of the principal stress deviators), the minimum octahedral shear-strain rate has no dependence on stress configuration. This result supports the hypothesis that the flow of isotropic ice is dependent only on the second invariant of the stress tensor. This fundamental assumption has been used to provide a general description of ice-flow behaviour independent of the stress configuration (e.g. Nye, 1953; Glen, 1958; Budd, 1969). For the tertiary flow of anisotropic ice, the octahedral strain rate is stress-state dependent as a consequence of the developed crystal-orientation fabric, which is also stress-state dependent, and which develops with strain and rotation. The present tests indicate that the enhancement factor for steady-state tertiary octahedral shear-strain rate depends on the shear or compression fraction and varies from about 10 for simple shear (with zero compression) to about 3 for uniaxial compression (with zero shear).

Experimental study on the deformation microstructures and crystallographic preferred orientation of glaucophane and epidote in deformed epidote blueschist at high pressure

2021 ◽  
Author(s):  
Yong Park ◽  
Sejin Jung ◽  
Haemyeong Jung
Keyword(s):  
High Pressure ◽  
Shear Strain ◽  
Shear Plane ◽  
Preferred Orientation ◽  
Dislocation Creep ◽  
Shear Direction ◽  
Shear Strain Rate ◽  
High Shear ◽  
Crystallographic Preferred Orientation ◽  
Ebsd Technique

<p>To understand the crystallographic preferred orientation (CPO) of glaucophane and epidote and deformation microstructures at the top of a subducting slab in a warm subduction zone, deformation experiments of epidote blueschist were conducted in simple shear by using a modified Griggs apparatus. Deformation experiments were performed under high pressure (0.9–1.5 GPa), temperature (400–500 °C), shear strain (γ) in the range of 0.4–4.5, and shear strain rate of 1.5×10<sup>-5</sup>–1.8×10<sup>-4</sup> s<sup>-1</sup>. After experiments, CPO of minerals were determined by electron back-scattered diffraction (EBSD) technique, and microstructures of deformed minerals were observed by transmission electron microscopy (TEM). At low shear strain (γ ≤ 1), the [001] axes of glaucophane were in subparallel alignment to shear direction, and the (010) poles were sub-normally aligned to the shear plane. At high shear strain (γ > 2), the [001] axes of glaucophane were in subparallel alignment to shear direction, and the [100] axes were sub-normally aligned to the shear plane. At a shear strain between 2 < γ < 4, the (010) poles of epidote were in subparallel alignment to shear direction, and the [100] axes were sub-normally aligned to the shear plane. At a high shear strain where γ > 4, the alignment of the (010) epidote poles had altered from subparallel to subnormal to the shear plane, while the [001] axes were in subparallel alignment to the shear direction. TEM observations and EBSD mapping revealed that the CPO of glaucophane was developed by dislocation creep, somewhat affected by the cataclastic flow at high shear strain. On the other hand, the CPO development of epidote is considered to have been affected by dislocation creep under a shear strain of 2 < γ < 4 but is highly affected by cataclastic flow with rigid body rotation under a high shear strain (γ > 4). Our experimental results indicate that the magnitude of shear strain and rheological contrast between component minerals plays an important role on the formation of CPOs of glaucophane and epidote.</p>

Effective rheology of a two-phase subduction shear zone: insights from numerical simple shear experiments and implications for subduction zone interfaces

2021 ◽  
Author(s):  
Paraskevi Io Ioannidi ◽  
Laetitia Le Pourhiet ◽  
Philippe Agard ◽  
Samuel Angiboust ◽  
Onno Oncken
Keyword(s):  
Simple Shear ◽  
Large Scale ◽  
Confining Pressure ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Small Scale ◽  
Two Phase ◽  
Weak Phase ◽  
Pure Phases ◽  
Geodynamic Models

<p>Exhumed subduction shear zones often exhibit block-in-matrix structures comprising strong clasts within a weak matrix (mélanges). Inspired by such observations, we create synthetic models with different proportions of strong clasts and compare them to natural mélange outcrops. We use 2D Finite Element visco-plastic numerical simulations in simple shear kinematic conditions and we determine the effective rheology of a mélange with basaltic blocks embedded within a wet quartzitic matrix. Our models and their structures are scale-independent; this allows for upscaling published field geometries to km-scale models, compatible with large-scale far-field observations. By varying confining pressure, temperature and strain rate we evaluate effective rheological estimates for a natural subduction interface. Deformation and strain localization are affected by the block-in-matrix ratio. In models where both materials deform viscously, the effective dislocation creep parameters (A, n, and Q) vary between the values of the strong and the weak phase. Approaching the frictional-viscous transition, the mélange bulk rheology is effectively viscous creep but in the small scale parts of the blocks are frictional, leading to higher stresses. This results in an effective value of the stress exponent, n, greater than that of both pure phases, as well as an effective viscosity lower than the weak phase. Our effective rheology parameters may be used in large scale geodynamic models, as a proxy for a heterogeneous subduction interface, if an appropriate evolution law for the block concentration of a mélange is given.</p>

High shear strain rate rheometry of polymer melts

2009 ◽  
Vol 114 (2) ◽  
pp. 864-873 ◽  
Author(s):  
A. L. Kelly ◽  
T. Gough ◽  
B. R. Whiteside ◽  
P. D. Coates
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Polymer Melts ◽  
Shear Strain Rate ◽  
High Shear
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