scholarly journals Comparison between experiment and computer modelling of plane-strain simple-shear ice deformation

1994 ◽  
Vol 40 (134) ◽  
pp. 46-55
Author(s):  
C.J. L. Wilson ◽  
Y. Zhang
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Simple Shear ◽  
Computer Modelling ◽  
Boundary Migration ◽  
Stress And Strain ◽  
Grain Boundary Migration ◽  
Lattice Orientation ◽  
Polycrystalline Ice ◽  
Good Agreement

AbstractAn examination of both experiments and computer models of polycrystalline ice undergoing a simple shear suggests that there is good agreement. The model has correctly reproduced the deformational and microstructural features caused by glide on (0001) in the ice aggregates. This success is particularly prominent for those ice grains with a lattice orientation suitable for hard or easy glide or kinking, and where there is a sub-horizontal с axis and a larger grain-size. A limitation may be that the model cannot explicitly simulate recrystallization and grain-boundary migration, which are two other important processes operating jointly with glide in experimentally deformed ice. However, through the use of the models, it is possible to show how kinematic factors can control the processes of recrystallization. The localization of recrystallization in the polycrystalline ice aggregate is determined by the stress and strain variations between neighbouring grains.

scholarly journals Comparison between experiment and computer modelling of plane-strain simple-shear ice deformation

1994 ◽  
Vol 40 (134) ◽  
pp. 46-55 ◽  
Author(s):  
C.J. L. Wilson ◽  
Y. Zhang
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Simple Shear ◽  
Computer Modelling ◽  
Boundary Migration ◽  
Stress And Strain ◽  
Grain Boundary Migration ◽  
Lattice Orientation ◽  
Polycrystalline Ice ◽  
Good Agreement

AbstractAn examination of both experiments and computer models of polycrystalline ice undergoing a simple shear suggests that there is good agreement. The model has correctly reproduced the deformational and microstructural features caused by glide on (0001) in the ice aggregates. This success is particularly prominent for those ice grains with a lattice orientation suitable for hard or easy glide or kinking, and where there is a sub-horizontalсaxis and a larger grain-size. A limitation may be that the model cannot explicitly simulate recrystallization and grain-boundary migration, which are two other important processes operating jointly with glide in experimentally deformed ice. However, through the use of the models, it is possible to show how kinematic factors can control the processes of recrystallization. The localization of recrystallization in the polycrystalline ice aggregate is determined by the stress and strain variations between neighbouring grains.

Deformation mechanisms in natural dolomite mylonites from a detachment system (Mt. Hymittos, Greece)

2021 ◽  
Author(s):  
Mark Coleman ◽  
Bernhard Grasemann ◽  
David Schneider ◽  
Konstantinos Soukis ◽  
Riccardo Graziani
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Boundary Migration ◽  
Size Reduction ◽  
Greenschist Facies ◽  
Normal Faults ◽  
Grain Boundary Migration ◽  
Grain Sizes ◽  
Subgrain Rotation ◽  
Middle Unit

<p>Microstructures may be used to determine the processes, conditions and kinematics under which deformation occurred. For a given set of these variables, different microstructures are observed in various materials due to the material’s physical properties. Dolomite is a major rock forming mineral, yet the mechanics of dolomite are understudied compared to other ubiquitous minerals such as quartz, feldspar, and calcite. Our new study uses petrographic, structural and electron back scatter diffraction analyses on a series of dolomitic and calcitic mylonites to document differences in deformation styles under similar metamorphic conditions. The Attic-Cycladic Crystalline Complex, Greece, comprises a series of core complexes wherein Miocene low-angle detachment systems offset and juxtapose a footwall of high-pressure metamorphosed rocks against a low-grade hanging wall. This recent tectonic history renders the region an excellent natural laboratory for studying the interplay of the processes that accommodate deformation. The bedrock of Mt. Hymittos, Attica, preserves a pair of ductile-then-brittle normal faults dividing a tripartite tectonostratigraphy. Field observations, mineral assemblages and observable microstructures suggests the tectonic packages decrease in metamorphic grade from upper greenschist facies (~470 °C at 0.8 GPa) in the stratigraphically lowest package to sub-greenschist facies in the stratigraphically highest package. Both low-angle normal faults exhibit cataclastic fault cores that grade into the schists and marbles of their respective hanging walls. The middle and lower tectonostratigraphic packages exhibit dolomitic and calcitic marbles that experienced similar geologic histories of subduction and exhumation. The mineralogically distinct units (calcite vs. dolomite) of the middle package deformed via different mechanisms under the same conditions within the same package and may be contrasted with mineralogically similar units that deformed under higher pressure and temperature conditions in the lower package. In the middle unit, dolomitic rocks are brittlely deformed. Middle unit calcitic marble are mylonitic to ultramylonitic with average grain sizes ranging from 30 to 8 μm. These mylonites evince grain-boundary migration and grain size reduction facilitated by subgrain rotation. Within the lower package, dolomitic and calcitic rocks are both mylonitic to ultramylonitic with grain sizes ranging from 28 to 5 μm and preserve clear crystallographic preferred orientation fabrics. Calcitic mylonites exhibit deformation microstructures similar to those of the middle unit. Distinctively, the dolomitic mylonites of the lower unit reveal ultramylonite bands cross-cutting and overprinting an older coarser mylonitic fabric. Correlated missorientation angles suggest these ultramylonites show evidence for grain size reduction accommodated by microfracturing and subgrain rotation. In other samples the dolomitic ultramylonite is the dominant fabric and is overprinting and causing boudinage of veins and relict coarse mylonite zones. Isolated interstitial calcite grains within dolomite ultramylonites are signatures of localized creep-cavitation processes. Following grain size reduction, grain boundary sliding dominantly accommodated further deformation in the ultramylonitic portions of the samples as indicated by randomly distributed correlated misorientation angles. This study finds that natural deformation of dolomitic rocks may occur by different mechanisms than those identified by published experiments; notably that grain-boundary migration and subgrain rotation may be active in dolomite at much lower temperatures than previously suggested.</p>

scholarly journals Development of microstructure in the high-temperature deformation of ice

1996 ◽  
Vol 23 ◽  
pp. 293-302 ◽  
Author(s):  
Christopher J. L. Wilson ◽  
Yanhua Zhang
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Time Lapse ◽  
Grain Structure ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Grain Boundary Migration ◽  
Crystallographic Slip ◽  
Polycrystalline Ice ◽  
Time Lapse Photography

Microstructural changes in three sets of experiments involving crystallographic slip in anisotropic polycrystalline ice are described and interpreted with the aid of computer models. The development of microstructure was followed using time-lapse photography and transmitted light observations with deformation undertaken in plane strain and at a temperature of approximately –1°C. The deformation within a grain aggregate that accompanies axial shortening is always heterogeneous on a grainscale. The extent of inhomogeneity varies depending on the pre-existing grain structure and the way it can accommodate intragranular slip. Grain interactions are extremely important in determining the bulk deformation and the degree of grain-boundary migration. A consequence of shortening of the aggregate is the formation of high stresses between neighbouring grains and under the appropriate conditions there may be either grain-boundary migration or melting at these sites. Where a sample undergoes translation and shear during deformation, anisotropic grains in the appropriate orientation undergo bending. A buckle instability may then develop and much of the strain is accommodated by grains in easy-glide orientations. In such situations, the ice undergoes extensive recrystallization and grain growth that is concentrated in the areas of greatest buckling.

scholarly journals Development of microstructure in the high-temperature deformation of ice

1996 ◽  
Vol 23 ◽  
pp. 293-302 ◽  
Author(s):  
Christopher J. L. Wilson ◽  
Yanhua Zhang
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Time Lapse ◽  
Grain Structure ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Grain Boundary Migration ◽  
Crystallographic Slip ◽  
Polycrystalline Ice ◽  
Time Lapse Photography

Microstructural changes in three sets of experiments involving crystallographic slip in anisotropic polycrystalline ice are described and interpreted with the aid of computer models. The development of microstructure was followed using time-lapse photography and transmitted light observations with deformation undertaken in plane strain and at a temperature of approximately –1°C. The deformation within a grain aggregate that accompanies axial shortening is always heterogeneous on a grainscale. The extent of inhomogeneity varies depending on the pre-existing grain structure and the way it can accommodate intragranular slip. Grain interactions are extremely important in determining the bulk deformation and the degree of grain-boundary migration. A consequence of shortening of the aggregate is the formation of high stresses between neighbouring grains and under the appropriate conditions there may be either grain-boundary migration or melting at these sites. Where a sample undergoes translation and shear during deformation, anisotropic grains in the appropriate orientation undergo bending. A buckle instability may then develop and much of the strain is accommodated by grains in easy-glide orientations. In such situations, the ice undergoes extensive recrystallization and grain growth that is concentrated in the areas of greatest buckling.

scholarly journals Fish Antifreeze Proteins and the Creep of Polycrystalline Ice

1988 ◽  
Vol 34 (118) ◽  
pp. 291-292 ◽  
Author(s):  
John W. Glen ◽  
David J. Ives
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Antifreeze Proteins ◽  
Nucleation And Growth ◽  
Tertiary Creep ◽  
Grain Boundary Migration ◽  
Low Concentrations ◽  
Creep Curves ◽  
Polycrystalline Ice

Abstract Creep curves obtained from the polycrystalline ice samples containing low concentrations of antifreeze glycopeptides (AFGPs) do not show the re-accelerating or tertiary creep that is found in pure ice samples. Previous work has shown that AFGPs inhibit grain-boundary migration in ice and the present results are consistent with this, as tertiary creep is associated with nucleation and growth of new ice grains.

The flow of polycrystalline lead under simple shear at higher temperatures

1968 ◽  
Vol 304 (1476) ◽  
pp. 1-24
Keyword(s):  
Grain Boundary ◽  
Tensile Stress ◽  
Simple Shear ◽  
Transient Flow ◽  
Boundary Migration ◽  
Grain Boundary Migration ◽  
Boundary Slip ◽  
Transition Stress ◽  
Constant Rate ◽  
Small Flow

The flow of polycrystalline lead has been investigated in detail by the method of simple shear, as used by Andrade & Jolliffe, at temperatures from 27 to 80 °C and also at 150 °C. Pre­liminary work on the variation of stable grain size with temperatures has shown that at 150 °C there are very few grains to the thickness of the metal annulus subject to shear, which is why this temperature is distinguished from the others. The range of temperature of the detailed measurements appears to be one of particular significance. The t 1/2 formula followed, as strain increases, by a t 1/3 formula, which has been shown to represent in detail the transient flow at 27 °C, has proved to be valid at all the higher temperatures and the laws governing the variation of the constants of the formulae with stress and temperature have been determined. At temperatures approaching 80 °C the flow so expressed is accompanied by a small flow linear with time, the laws of which have been determined. This linear flow has been traced to grain boundary slip, which is not involved in the t 1/2 and t 1/3 flow. Particular attention has been paid to stage III of the flow, in which the metal has the properties of a non-Newtonian fluid. The constant rate of flow has been expressed in terms of a function of the velocity and temperature which is linear with stress. It has been shown that at a certain transition stress the slope of the line changes abruptly. This transition stress is a simple function of the temperature. Photomicrographs showing the deformation of the surface grains, which with the method employed, but not with the method of tensile stress, is held to be typical of the behaviour of internal grains, have thrown some light on the processes associated with the various stages of flow. An intermittent grain boundary migration has been established at higher temperatures. The results obtained by the method of simple shear are compared with the results of tests carried out by the usual method of tensile stress with rods or wires, from which they differ in certain significant respects, such as the conditions leading to recrystallization and the accompanying effects.

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.

Understanding Grain Boundary Junctions: Effect of the Grain Size on Microstructure Evolution

2012 ◽  
Vol 715-716 ◽  
pp. 186-190 ◽  
Author(s):  
Luis A. Barrales Mora ◽  
Lasar S. Shvindlerman ◽  
Günter Gottstein
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Microstructure Evolution ◽  
Boundary Migration ◽  
Granular System ◽  
Grain Boundary Migration ◽  
Triple Junctions ◽  
Model Simulations ◽  
Grain Sizes

In a previous work [ we introduced the geometry of a granular system that allowed the study of the effect of a finite mobility of the quadruple and triple junctions on grain boundary migration. One of the most important conclusions of this work was that the triple junctions drag more effectively the motion of the grain boundaries than the quadruple junctions. Nevertheless, this conclusion was drawn without consideration of the grain size. For this reason, this conclusion might be contradictory with our understanding of the grain boundary junctions because while the effect of the triple lines is inverse linear with the grain size that of the quadruple junctions is proportional to the inverse square of the grain size and thus, quadruple junctions are expected to drag more effectively, at least, for very small grain sizes. In the present investigation, we studied comprehensively the effect of grain size on the evolution of the granular system under the assumption of a finite mobility of the boundary junctions. For this purpose, several network model simulations were carried out for different grain sizes ranging from nanoto micrometers using a fully periodic grain arrangement. The results seem to corroborate that the triple junctions drag more effectively the motion of the grain boundaries, however, for very low junction mobility and grain sizes the effect appears to be indistinguishable. It was also observed that for very low quadruple junction mobility the geometry of the granular system undergoes a severe transformation which results in the unfulfillment of the equation derived in [.

Fabric and origin of gneissic layers in anorthositic rocks of the St. Charles sill, Ontario

1981 ◽  
Vol 18 (11) ◽  
pp. 1681-1693 ◽  
Author(s):  
D. H. Rousell
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Strain Rate ◽  
Boundary Diffusion ◽  
Boundary Migration ◽  
Diffusion Mechanism ◽  
Coarse Grained ◽  
Grain Boundary Migration ◽  
Grenville Province ◽  
Fine Grained

The St. Charles sill is located in the Grenville Province and consists of rocks of the anorthosite suite. The sill is a northwesterly trending body, 11 km long and as much as 0.8 km wide, and with a steep dip to the northeast. The sill is characterized by interlayered massive and gneissic rocks metamorphosed under conditions of the amphibolite facies. In the massive rocks plagioclase occurs as strongly twinned laths that range in size from fine-grained crystals to megacrysts. Hornblende, biotite, and garnet occur as subophitic masses and apparently replace original pyroxene. In the gneissic rocks the plagioclase ranges in size from fine to coarse grained and the primary grains are partially replaced by elongate, weakly twinned, anhedral plagioclase. The gneissosity is defined by a dimensional preferred orientation of biotite, hornblende, and secondary plagioclase. The formation of the secondary plagioclase is attributed largely to growth by grain boundary diffusion and, to a lesser extent, by replacement of primary plagioclase by grain boundary migration. In the diffusion mechanism strain rate is inversely proportional to grain size and it is interpreted that the tectonic fabric developed in the finer grained layers of the sill while the coarser grained layers remained essentially undeformed.

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