scholarly journals The Fabric of Polycrystalline Ice Deformed in Simple Shear: Experiments in Torsion, Natural Deformation and Geometrical Interpretation

1982 ◽  
Vol 5 (3) ◽  
pp. 171-190 ◽  
Author(s):  
J. L. Bouchez ◽  
P. Duval
Keyword(s):  
Computer Model ◽  
Simple Shear ◽  
Basal Plane ◽  
Shear Plane ◽  
Bimodal Distribution ◽  
Random Lattice ◽  
Minimum Concentration ◽  
Strain Ellipsoid ◽  
Polycrystalline Ice ◽  
Slip Planes

Three cylinders of artificial ice have been deformed in torsion at about –10℃ up to finite shear strains γ of 0.6, 0.95 and 2. The initial random lattice orientation rapidly evolves into a bimodal distribution of the basal slip planes as already observed by Kamb (1972) and Duval (1981) for low-strains experiments near the melting point. For the γ = 0.6 and 0.95 experiments, one family of grains (> 50%) corresponds to basal planes tending to parallel the imposed shear plane; the basal planes of the other family make a broader maximum at about 60° from the shear plane. The direction of minimum concentration between the two populations approximately corresponds to the flattening plane or to the elongation direction of the strain ellipsoid. With increasing strain (γ = 2) the second submaximum vanishes and only the principal maximum parallel to the shear plane remains. This evolution is conformable with the data of Hudleston (1977) in a natural shear zone in glacial ice; it also compares remarkably well with Etchecopar's (1977) geometrical computer model of simple shear in the same range of γ values. Single slip on the basal plane with no preferential slip direction in that plane can explain the analogy between fabrics in ice deformed in plane strain and fabrics obtained from the two-dimensional computer model.The bimodal distribution reflects predominant slip on the basal plane; the progressively increasing heterogeneous strain enhances internal distorsion, rigid body rotation and recrystallization of grains unfavorably oriented for further slip, leading to the unimodal distribution. The adequacy of fabric analyses to infer the strain regime and the sense of shear in plastically deformed rocks is strengthened.

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 Microstructure and Texture Inhomogeneity after Large Non-Monotonic Simple Shear Strains: Achievements of Tensile Properties

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 583 ◽  
Author(s):  
Ebad Bagherpour ◽  
Fathallah Qods ◽  
Ramin Ebrahimi ◽  
Hiroyuki Miyamoto
Keyword(s):  
Tensile Properties ◽  
Simple Shear ◽  
Shear Plane ◽  
Continuous Dynamic Recrystallization ◽  
Slip Planes ◽  
Plane Change ◽  
Shear Strains ◽  
Continuous Dynamic ◽  
Simple Shear Extrusion ◽  
Pure Cu

In this study, for the first time, the effect of large non-monotonic simple shear strains on the uniformity of the tensile properties of pure Cu specimens was studied and justified by means of microstructural and textural investigations. A process called simple shear extrusion, which consists of two forward and two reversed simple shear straining stages on two different slip planes, was designed in order to impose non-monotonic simple shear strains. Although the mechanism of grain refinement is continuous dynamic recrystallization, an exceptional microstructural behavior and texture were observed due to the complicated straining path results from two different slip planes and two pairs of shear directions on two different axes in a cycle of the process. The geometry of the process imposes a distribution of strain results in the inhomogeneous microstructure and texture throughout the plane perpendicular to the slip plane. Although it is expected that the yield strength in the periphery reaches that of the center by retardation, it never reaches that value, which results in the different deformation modes of the center and the periphery. The occurrence of shear reversal in each quarter of a cycle results in the elimination of some of the boundaries, an increase in the cell wall thickness, and a decrease in the Taylor factor. Change in the shear plane in each half of a cycle leads to the formation of cell boundaries in a different alignment. Since the direction of the shear and/or the shear plane change frequently in a cycle, the texture of a sample after multi-cycles of the process more closely resembles a random orientation.

scholarly journals Microstructure and texture evolution in polycrystalline ice during hot torsion. Impact of intragranular strain and recrystallization processes

2018 ◽  
Author(s):  
Baptiste Journaux ◽  
Thomas Chauve ◽  
Maurine Montagnat ◽  
Andrea Tommasi ◽  
Fabrice Barou ◽  
...  
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Grain Boundaries ◽  
Simple Shear ◽  
Texture Evolution ◽  
Boundary Migration ◽  
Shear Plane ◽  
Dislocation Slip ◽  
Polycrystalline Ice

Abstract. Torsion experiments were performed in polycrystalline ice at high temperature (0.97 ⋅ Tm) to reproduce simple shear conditions close to those encountered in ice streams and at the base of fast flowing glaciers. As well documented more than 30 years ago (Hudleston, 1977; Bouchez and Duval, 1982), under simple shear ice develops a two-maxima c-axis texture, which evolves rapidly into a single cluster texture with c-axis perpendicular to the shear plane. This evolution still lacks a physical explanation. Current viscoplastic modeling approaches on ice involving dislocation slip on multiple slip systems (basal pyramidal, and prismatic) fail to reproduce it. Dynamic recrystallization mechanisms that occur in both laboratory conditions and in natural setups are likely candidates to explain the texture evolution observed. In this study, we use Electron BackScattering 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 by dislocations with [c]-component Burgers vector, indicating that strong local stress heterogeneity develops, even at high temperature and high finite shear strain. Based on these observations, we propose that that nucleation by bulging, assisted by sub-grain boundary formation, is a very likely candidate to explain the progressive disappearance of the texture 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 models limiting dislocation slip on non-basal slip system and allowing for efficient polygonization by an association of bulging and formation of sub-grain boundaries with a significant [c]-component.

Stable equilibrium configurations of an oblate capsule in simple shear flow

2016 ◽  
Vol 791 ◽  
pp. 738-757 ◽  
Author(s):  
C. Dupont ◽  
F. Delahaye ◽  
D. Barthès-Biesel ◽  
A.-V. Salsac
Keyword(s):  
Aspect Ratio ◽  
Shear Flow ◽  
Simple Shear ◽  
Capillary Number ◽  
Stable Equilibrium ◽  
Viscosity Ratio ◽  
Shear Plane ◽  
Initial Orientation ◽  
Simple Shear Flow ◽  
Mechanical Equilibrium

The objective of the paper is to determine the stable mechanical equilibrium states of an oblate capsule subjected to a simple shear flow, by positioning its revolution axis initially off the shear plane. We consider an oblate capsule with a strain-hardening membrane and investigate the influence of the initial orientation, capsule aspect ratio$a/b$, viscosity ratio${\it\lambda}$between the internal and external fluids and the capillary number$Ca$which compares the viscous to the elastic forces. A numerical model coupling the finite element and boundary integral methods is used to solve the three-dimensional fluid–structure interaction problem. For any initial orientation, the capsule converges towards the same mechanical equilibrium state, which is only a function of the capillary number and viscosity ratio. For$a/b=0.5$, only four regimes are stable when${\it\lambda}=1$: tumbling and swinging in the low and medium$Ca$range ($Ca\lesssim 1$), regimes for which the capsule revolution axis is contained within the shear plane; then wobbling during which the capsule experiences precession around the vorticity axis; and finally rolling along the vorticity axis at high capillary numbers. When${\it\lambda}$is increased, the tumbling-to-swinging transition occurs for higher$Ca$; the wobbling regime takes place at lower$Ca$values and within a narrower$Ca$range. For${\it\lambda}\gtrsim 3$, the swinging regime completely disappears, which indicates that the stable equilibrium states are mainly the tumbling and rolling regimes at higher viscosity ratios. We finally show that the$Ca$–${\it\lambda}$phase diagram is qualitatively similar for higher aspect ratio. Only the$Ca$-range over which wobbling is stable increases with$a/b$, restricting the stability ranges of in- and out-of-plane motions, although this phenomenon is mainly visible for viscosity ratios larger than 1.

Basal Plane Dislocation Multiplication via the Hopping Frank-Read Source Mechanism and Observations of Prismatic Glide in 4H-SiC

2012 ◽  
Vol 717-720 ◽  
pp. 327-330 ◽  
Author(s):  
Huan Huan Wang ◽  
Sha Yan Byrapa ◽  
F. Wu ◽  
Balaji Raghothamachar ◽  
Michael Dudley ◽  
...  
Keyword(s):  
Shear Stress ◽  
Slip Plane ◽  
Opposite Direction ◽  
Edge Dislocation ◽  
Basal Plane ◽  
Detailed Mechanism ◽  
Slip Planes ◽  
Basal Plane Dislocation ◽  
Edge Dislocations ◽  
Dislocation Multiplication

In this paper, we report on the synchrotron white beam topographic (SWBXT) observation of “hopping” Frank-Read sources in 4H-SiC. A detailed mechanism for this process is presented which involves threading edge dislocations experiencing a double deflection process involving overgrowth by a macrostep (MP) followed by impingement of that macrostep against a step moving in the opposite direction. These processes enable the single-ended Frank-Read sources created by the pinning of the deflected basal plane dislocation segments at the less mobile threading edge dislocation segments to “hop” from one slip plane to other parallel slip planes. We also report on the nucleation of 1/3< >{ } prismatic dislocation half-loops at the hollow cores of micropipes and their glide under thermal shear stress.

The Reorientation of the Kangâmiut Dike Swarm, West Greenland

1975 ◽  
Vol 12 (2) ◽  
pp. 158-173 ◽  
Author(s):  
A. Escher ◽  
J. C. Escher ◽  
J. Watterson
Keyword(s):  
Simple Shear ◽  
Shear Plane ◽  
Boundary Region ◽  
Ductile Deformation ◽  
Shear Direction ◽  
Average Amount ◽  
Southern Boundary ◽  
Crustal Shortening ◽  
West Greenland ◽  
Simple Shear Deformation

The Nagssugtoqidian belt in West Greenland is formed mainly of Archaean rocks which were strongly reworked during the early Proterozoic. Investigation of the southern boundary region has resulted in a model for the tectonic reworking based on the geometry of homogeneous simple shear deformation. Two differently oriented swarms of mainly pre-kinematic dikes are used as strain indicators at the deformation boundary. Gneiss tectonite fabrics have been used to determine that the shear plane dips northwest at 20–40° and that the shear direction along this plane is towards the southeast. The average amount of simple shear strain (S = 6) has been determined from the degree of dike reorientation. This mechanism has resulted in a ductile overthrusting of the reworked rocks over the Archaean foreland, giving a crustal shortening of ca. 66%. The area investigated represents a deep tectonic level. At higher levels ductile deformation would be expected to give way to thrust and fold nappe development. The displacements demonstrated are those which might be expected in the deformed margins of colliding continental plates.

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.

Shear Deformation and Texture Evolution in Al Alloys Processed for One Pass by ECAP

2008 ◽  
Vol 584-586 ◽  
pp. 679-684 ◽  
Author(s):  
Marco J. Starink ◽  
Shun Cai Wang ◽  
Xiao Guang Qiao ◽  
Nong Gao ◽  
Hans Jørgen Roven ◽  
...  
Keyword(s):  
Shear Deformation ◽  
Texture Evolution ◽  
Shear Plane ◽  
Al Alloys ◽  
Coarse Grained ◽  
Al Alloy ◽  
Shear Direction ◽  
Crystallographic Slip ◽  
Slip Planes ◽  
Low Strength

The evolution of texture and deformation in the grains during one pass of equal-channel angular pressing (ECAP) was examined for fine grained high strength and low strength Al alloys and a coarse grained low strength Al alloy. The materials were analysed using electron back-scatter diffraction (EBSD). The results are consistent with the materials responding to the intense macroscopic shear stress by deformation of individual grains through movement of dislocations on one or more of the slip crystallographic slip planes {hkl} that are favourably oriented, combined with the rotation of grains to directions that bring main crystallographic slip planes parallel to the macroscopic shear direction and crystallographic slip directions <uvw> parallel to two main shear directions. Contrary to reports claiming up to 4 slip systems are activated, it was observed that only the {111}<110> and {001}<110> shear systems are activated. Macroscopic shear deformation occurs on two shear planes: the main shear plane (MSP), equivalent to the simple shear plane, and a secondary shear plane which is perpendicular to the MSP.

scholarly journals DEPENDENCE OF CRACK FORMATION ON CRYSTALLOGRAPHIC ORIENTATION FOR ICE

1966 ◽  
Vol 44 (11) ◽  
pp. 2757-2764 ◽  
Author(s):  
L. W. Gold
Keyword(s):  
Grain Boundary ◽  
Crystallographic Orientation ◽  
Basal Plane ◽  
Applied Load ◽  
Crack Formation ◽  
Compressive Load ◽  
Slip Systems ◽  
Polycrystalline Ice ◽  
Minimum Number ◽  
Columnar Grain

Observations are reported of crack propagation in columnar-grain, polycrystalline ice subjected to constant compressive load applied perpendicular to the long axis of the columns. About three-quarters of the cracks observed were transcrystalline and the remainder occurred at grain boundaries. The plane of the cracks tended to be parallel to the direction of the applied load. Transcrystalline cracks tended to propagate either parallel or perpendicular to the basal plane. At least two-thirds of the grain boundary cracks were associated with boundaries for which the slip plane of one or both of the adjacent grains was close to parallel or perpendicular to the boundary. It is shown that the observations are consistent with the hypothesis that a minimum number of independent slip systems are required for a grain to conform to an arbitrary deformation under constraints imposed by neighboring grains.

The Characteristic Grain Size and the Compressive Strength of Ice Containing a Bimodal Distribution of Grain Sizes

1989 ◽  
Vol 111 (1) ◽  
pp. 61-62
Author(s):  
E. M. Schulson ◽  
J. L. Laughlin
Keyword(s):  
Grain Size ◽  
Compressive Strength ◽  
Grain Refinement ◽  
Bimodal Distribution ◽  
Grain Sizes ◽  
Freshwater Ice ◽  
Polycrystalline Ice

The purpose of this communication is to show through experiment that the compressive strength of polycrystalline ice, which contains a bimodal distribution of grain sizes, can be expressed in terms of a characteristic grain size. The work was performed in response to an awareness that grain refinement strengthens both columnar [1] and granular [2] freshwater ice deformed under compression, and that ice formed naturally often contains grains of more than one size. A detailed discussion is given elsewhere [3].

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