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.

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.

FRACTAL GRAIN BOUNDARY MIGRATION

Fractals ◽  
2000 ◽  
Vol 08 (02) ◽  
pp. 189-194 ◽  
Author(s):  
MIKI TAKAHASHI ◽  
HIROYUKI NAGAHAMA
Keyword(s):  
Grain Boundary ◽  
Strain Rate ◽  
Grain Boundaries ◽  
Boundary Migration ◽  
Empirical Relationship ◽  
Grain Boundary Migration ◽  
Dynamics Model ◽  
Cell Dynamics ◽  
Hollomon Parameter ◽  
Dimension Analysis

Fractal analysis on experimentally recrystallized quartz grain boundaries has been employed to relate the grain boundary complexities with deformation conditions, such as strain rate and temperature. The fractal dimensional increment of the grain boundaries, defined as (D-1), and the degree of irregularity in grain boundaries, is proportional to the logarithmic of the Zener–Hollomon parameter that is defined by strain rate and temperature (the Arrhenius term). The physical mean of the empirical relationship can be explained theoretically by a new grain boundary migration model (GBM or cell dynamics model) extended by the fractal concepts and the dimension analysis. This is a more general model than the migration growth model for the fractal grain boundaries.

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>

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

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.

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 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.

Development of interconnected fine-grained polyphase networks during progressive exhumation of a shear zone

2020 ◽  
Author(s):  
Alexander Lusk ◽  
John Platt
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Shear Zone ◽  
Strain Localization ◽  
Cooling System ◽  
Boundary Migration ◽  
Grain Boundary Sliding ◽  
Fine Grained ◽  
Subgrain Rotation ◽  
Boundary Sliding

<p>Present exposure of the ductile Caledonian retrowedge in northwestern Scotland records the evolution of a shear zone that was exhuming while actively deforming, providing a natural laboratory to study strain localization in a progressively cooling system. Examination of rocks from two detailed transects across this region consistently show a transition from microstructures that are dominated by interconnected phyllosilicate networks in a quartz-rich matrix with feldspar porphyroclasts, to interconnected fine-grained regions of mixed quartz + phyllosilicate + feldspar. These polyphase regions are demonstrably weaker than surrounding quartz layers and likely deform by grain-size sensitive mechanisms including diffusion-accommodated grain boundary sliding.</p><p>Microstructures characterized by a quartz-rich matrix and interconnected phyllosilicates undergo quartz recrystallization by high temperature grain boundary migration and are dominated by prism <em>a</em> slip. In contrast, fine-grained polyphase microstructures record quartz recrystallization dominated by subgrain rotation and activation of rhomb <em>a</em> and basal <em>a</em> slip systems. We propose transient hardening occurs in quartz-dominated regions as quartz with a strong Y-axis maximum undergoes the switch from prism <em>a</em> easy slip to basal <em>a</em> easy slip during cooling, and thus partitions strain into interconnected phyllosilicate layers. In response, interconnected phyllosilicate layers undergo mechanical comminution, becoming increasingly mixed by grain-size sensitive creep processes to form polyphase layers as they accommodate an increased proportion of strain. This transition from quartz-rich matrix with phyllosilicate interconnected weak layers to fine-grained, polyphase weak layers could be of first-order importance in strain localization within polyphase mylonitic and ultramylonitic rocks.</p>

Effect of Processing Temperature on Microstructure Development during ECAP of Al-Mg-Sc Alloy

2008 ◽  
Vol 584-586 ◽  
pp. 481-486 ◽  
Author(s):  
Oleg Sitdikov ◽  
Elena Avtokratova ◽  
Taku Sakai ◽  
Kaneaki Tsuzaki ◽  
Rustam Kaibyshev ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Boundary Migration ◽  
Grain Structure ◽  
Coarse Grained ◽  
Microstructural Development ◽  
Al Alloy ◽  
Processing Temperature ◽  
Fine Grained ◽  
Grain Boundary Mobility ◽  
Angular Pressing

Microstructural evolution taking place during equal channel angular pressing (ECAP) was studied in a commercial coarse-grained Al-6%Mg-0.4%Mn-0.3%Sc alloy in a temperature interval 200- 450oC (~0.5-0.8 Tm). Samples were pressed using route A to a total strain of 12 and quenched in water after each ECAP pass. Uniform fine-grained microstructures with the average grain sizes of 0.7 and 2.5 0m, are almost fully evolved at high ECAP strains at 250oC and 450oC, respectively, while ECAP at 300oC (~0.6 Tm) leads to the formation of bimodal grain structure with fine grains of around 1 µm and relatively coarse grains of around 8 µm. The latter are developed due to the occurrence of static recrystallization during “keeping” time in the ECAP channel and/or reheating between ECAP passes. The microstructural development under warm-to-hot ECAP conditions is discussed in terms of the large potential for grain boundary migration resulted from an overlapping of accelerated grain boundary mobility at high pressing temperatures and enhanced driving force for recrystallization, which is caused by a strong inhibition of dynamic recovery in a heavily-alloyed Al alloy.

Effects of Strain Rate and Grain Size on Behavior of Nano Crystalline Materials

2012 ◽  
Vol 17 ◽  
pp. 35-51 ◽  
Author(s):  
Reza Jafari Nedoushan ◽  
Mahmoud Farzin ◽  
Mohammad Mashayekhi
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Coarse Grained ◽  
Crystalline Materials ◽  
Nano Crystalline

Recent Experiments on Nano-Crystalline Materials Show an Increase of Strain-Rate Sensitivity in Contrast to the Conventional Coarse-Grained Materials. these Materials Also Show a Different Grain Size Dependency as Compared to Coarse-Grained Materials. to Explain these Issues, a Constitutive Equation Is Proposed which Considers Dominant Deformation Mechanisms Including Grain Interior Plasticity, Grain Boundary Diffusion and Grain Boundary Sliding. the Stresses Obtained from these Constitutive Equations Match Well with the Experimental Data for Nanocrystalline Copper at Different Strains and Strain Rates. the Model Also Well Predicts Variation of Strain Rate Sensitivity Parameter. this Variation Can Be Explained with Regard to the above Mentioned Effective Deformation Mechanisms. Deviation from the Hall-Petch Law and Inverse Hall-Petch Effect Are Also Well Illustrated by the Model.

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