scholarly journals Effects of microparticles on deformation and microstructural evolution of fine-grained ice

2019 ◽  
Vol 65 (252) ◽  
pp. 531-541 ◽  
Author(s):  
TOMOTAKA SARUYA ◽  
KOKI NAKAJIMA ◽  
MORIMASA TAKATA ◽  
TOMOYUKI HOMMA ◽  
NOBUHIKO AZUMA ◽  
...  
Keyword(s):  
Grain Size ◽  
Particle Dispersion ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Compression Tests ◽  
Fine Grained ◽  
Mean Grain Size ◽  
Polycrystalline Ice ◽  
Order Of Magnitude ◽  
Deformation Processes

ABSTRACTWe investigated the effects of microparticles and grain size on the microstructural evolutions and mechanical properties of polycrystalline ice. Uniaxial compression tests were conducted using fine-grained pure ice and silica-dispersed ice under various conditions. Deformation behavior of fine-grained ice was found to be characterized by stress exponent n ≈ 2 and activation energy Q ≈ 60 kJ mol−1. The derived strain rates of fine-grained ice were ≈ 1 order of magnitude larger than those of coarse-grained ice obtained in previous studies, and they were found to be independent of particle dispersion and dependent on the mean grain size of ice, with grain size exponent p ≈ 1.4. Work hardening was observed in dislocation creep, while the strain rate continued to decrease. These results indicate that the deformation mechanism of fine-grained ice is different from typical dislocation creep, often associated with n = 3. Although microparticles restricted grain growth, there was little direct effect on the deformation of fine-grained ice. Microstructural observations of the ice samples indicated that the grain boundaries were straight and that the subgrain boundary densities increased after deformation. Our experiments suggest that grain size and boundaries play important roles in the deformation processes of polycrystalline ice.

scholarly journals Deformation of feldspar at greenschist facies conditions – the record of mylonitic pegmatites from the Pfunderer Mountains, Eastern Alps

Solid Earth ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 95-116 ◽  
Author(s):  
Felix Hentschel ◽  
Claudia A. Trepmann ◽  
Emilie Janots
Keyword(s):  
Grain Size ◽  
Granular Flow ◽  
Thin Layers ◽  
Size Reduction ◽  
Greenschist Facies ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Subsequent Growth ◽  
Dislocation Glide ◽  
Fine Grained

Abstract. Deformation microstructures of albitic plagioclase and K-feldspar were investigated in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window by polarized light microscopy, electron microscopy and electron backscatter diffraction to evaluate feldspar deformation mechanisms at greenschist facies conditions. The main mylonitic characteristics are alternating almost monophase quartz and albite layers, surrounding porphyroclasts of deformed feldspar and tourmaline. The dominant deformation microstructures of K-feldspar porphyroclasts are intragranular fractures at a high angle to the stretching lineation. The fractures are healed or sealed by polyphase aggregates of albite, K-feldspar, quartz and mica, which also occur along intragranular fractures of tourmaline and strain shadows around other porphyroclasts. These polyphase aggregates indicate dissolution–precipitation creep. K-feldspar porphyroclasts are partly replaced by albite characterized by a cuspate interface. This replacement is interpreted to take place by interface-coupled dissolution–precipitation driven by a solubility difference between K-feldspar and albite. Albite porphyroclasts are replaced at boundaries parallel to the foliation by fine-grained monophase albite aggregates of small strain-free new grains mixed with deformed fragments. Dislocation glide is indicated by bent and twinned albite porphyroclasts with internal misorientation. An indication of effective dislocation climb with dynamic recovery, for example, by the presence of subgrains, is systematically missing. We interpret the grain size reduction of albite to be the result of coupled dislocation glide and fracturing (low-temperature plasticity). Subsequent growth is by a combination of strain-induced grain boundary migration and formation of growth rims, resulting in an aspect ratio of albite with the long axis within the foliation. This strain-induced replacement by nucleation (associated dislocation glide and microfracturing) and subsequent growth is suggested to result in the observed monophase albite layers, probably together with granular flow. The associated quartz layers show characteristics of dislocation creep by the presence of subgrains, undulatory extinction and sutured grain boundaries. We identified two endmember matrix microstructures: (i) alternating layers of a few hundred micrometres' width, with isometric, fine-grained feldspar (on average 15 µm in diameter) and coarse-grained quartz (a few hundred micrometres in diameter), representing lower strain compared to (ii) alternating thin layers of some tens of micrometres' width composed of fine-grained quartz (<20 µm in diameter) and coarse elongated albite grains (long axis of a few tens of micrometres) defining the foliation, respectively. Our observations indicate that grain size reduction by strain-induced replacement of albite (associated dislocation glide and microfracturing) followed by growth and granular flow simultaneous with dislocation creep of quartz are playing the dominating role in formation of the mylonitic microstructure.

Microstructure Development and Ductility of Ultra-Fine Grained Mg-Gd Alloy Prepared by High Pressure Torsion

2009 ◽  
Vol 633-634 ◽  
pp. 353-363 ◽  
Author(s):  
Jakub Čížek ◽  
Ivan Procházka ◽  
Bohumil Smola ◽  
Ivana Stulíková ◽  
Vladivoj Očenášek ◽  
...  
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Elevated Temperatures ◽  
High Pressure Torsion ◽  
High Sensitivity ◽  
Tensile Tests ◽  
Lattice Defects ◽  
Coarse Grained ◽  
Fine Grained ◽  
Mean Grain Size

Microstructure of ultra fine grained (UFG) Mg-Gd alloy prepared by high-pressure torsion (HPT) was investigated in the present work. Lattice defects introduced by HPT were characterized at first. Subsequently thermal stability of UFG structure and its development with annealing temperature were studied and correlated with changes of hardness and ductility. Precipitation effects in the alloy with UFG structure were compared with those in a conventional coarse-grained alloy. Defect studies were performed by positron annihilation spectroscopy (PAS), which represents well established non-destructive technique with a high sensitivity to open volume lattice defects like vacancies, dislocations, misfit defects etc. PAS investigations were combined with transmission electron microscopy (TEM) and X-ray diffraction (XRD). Changes of mechanical properties were monitored by Vicker’s microhardness (HV) and deformation tensile tests. It was found that HPT deformed Mg-Gd alloy exhibits UFG structure with mean grain size of 100 nm and a dense network of dislocations distributed uniformly throughout the whole sample. Although recovery of dislocations takes place at relatively low temperatures, it is not accompanied by grain growth and the mean grain size remains around 100 nm up to 300oC. Tensile tests performed at elevated temperatures to examine ductility showed that HPT-deformed alloy exhibits a superplastic behavior at 400oC. Moreover, it was found that the precipitation sequence in HPT-deformed alloy differs from that in conventional coarse-grained material.

scholarly journals Deformation of feldspar at greenschist facies conditions – the record of mylonitic pegmatites from the Pfunderer Mountains, Eastern Alps

2018 ◽  
Author(s):  
Felix Hentschel ◽  
Claudia A. Trepmann ◽  
Emilie Janots
Keyword(s):  
Grain Size ◽  
Grain Boundaries ◽  
Granular Flow ◽  
Size Reduction ◽  
Greenschist Facies ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Crystallographic Preferred Orientation ◽  
Dislocation Glide ◽  
Fine Grained

Abstract. Deformation microstructures of albitic plagioclase and K-feldspar were investigated in mylonitic pegmatites from the Austroalpine basement south of the western Tauern Window by polarized light microscopy, electron microscopy and electron backscatter diffraction to evaluate the rheologically dominant feldspar deformation mechanisms at greenschist facies conditions. The main mylonitic characteristics are alternating almost monophase quartz and albite layers, surrounding porphyroclasts of deformed feldspar and tourmaline. The dominant deformation microstructures of K-feldspar porphyroclasts are intragranular fractures parallel to the main shortening direction indicated by the foliation. The fractures are healed or sealed by polyphase aggregates of albite, K-feldspar, quartz and mica, which also occur along intragranular fractures of tourmaline and strain shadows around other porphyroclasts. Polyphase aggregates at sites of dilation indicate dissolution-precipitation creep. K-feldspar porphyroclasts are partly replaced by albite characterized by a sawtooth-shaped interface. This replacement is interpreted to be by interface-coupled dissolution-precipitation driven by a solubility difference between K-feldspar and albite and is not controlled by strain. In contrast, albite porphyroclasts are replaced at sites of shortening by fine-grained monophase albite aggregates of small strain-free new grains mixed with deformed fragments. Dislocation glide is indicated by bent, kinked and twinned albite. No indication of effective dislocation climb with dynamic recovery, for example by the presence of subgrains, a crystallographic preferred orientation or sutured grain boundaries was observed. We interpret the grain size reduction of albite at sites of shortening to be the result of coupled fracturing, dislocation glide and strain-induced grain boundary migration. This strain-induced replacement by nucleation and growth leads, together with granular flow, to the monophase albite layers. The associated quartz layers in contrast, show characteristics of dislocation creep by the presence of subgrains, undulatory extinction and sutured grain boundaries. We identified two endmember matrix microstructures that correlate with strain. Samples with lower strain are characterized by layers of a few hundreds of µm width, with coarse-grained quartz and layers with isometric, fine-grained feldspar. Higher strained samples are characterized by narrow alternating layers of some tens of µm width composed of fine-grained quartz and coarse albite grains elongated parallel to the stretching lineation, respectively. These observations indicate that grain size reduction by strain-induced replacement of albite, granular flow assisted by fracturing and dissolution-precipitation together with dislocation creep of quartz are rheologically dominant.

scholarly journals Submarine lava deltas of the 2018 eruption of Kīlauea volcano

2021 ◽  
Vol 83 (4) ◽  
Author(s):  
S. Adam Soule ◽  
Michael Zoeller ◽  
Carolyn Parcheta
Keyword(s):  
Grain Size ◽  
Pore Pressure ◽  
Mechanistic Model ◽  
Large Fraction ◽  
Volcanic Hazards ◽  
Lava Flows ◽  
Coarse Grained ◽  
Fine Grained ◽  
Fine Grain ◽  
Delta Formation

AbstractHawaiian and other ocean island lava flows that reach the coastline can deposit significant volumes of lava in submarine deltas. The catastrophic collapse of these deltas represents one of the most significant, but least predictable, volcanic hazards at ocean islands. The volume of lava deposited below sea level in delta-forming eruptions and the mechanisms of delta construction and destruction are rarely documented. Here, we report on bathymetric surveys and ROV observations following the Kīlauea 2018 eruption that, along with a comparison to the deltas formed at Pu‘u ‘Ō‘ō over the past decade, provide new insight into delta formation. Bathymetric differencing reveals that the 2018 deltas contain more than half of the total volume of lava erupted. In addition, we find that the 2018 deltas are comprised largely of coarse-grained volcanic breccias and intact lava flows, which contrast with those at Pu‘u ‘Ō‘ō that contain a large fraction of fine-grained hyaloclastite. We attribute this difference to less efficient fragmentation of the 2018 ‘a‘ā flows leading to fragmentation by collapse rather than hydrovolcanic explosion. We suggest a mechanistic model where the characteristic grain size influences the form and stability of the delta with fine grain size deltas (Pu‘u ‘Ō‘ō) experiencing larger landslides with greater run-out supported by increased pore pressure and with coarse grain size deltas (Kīlauea 2018) experiencing smaller landslides that quickly stop as the pore pressure rapidly dissipates. This difference, if validated for other lava deltas, would provide a means to assess potential delta stability in future eruptions.

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 Size Effects Due to Specimen and Grain Size in Microbending

2010 ◽  
Vol 132 (1) ◽  
Author(s):  
Sunal Ahmet Parasiz ◽  
Reid VanBenthysen ◽  
Brad L. Kinsey
Keyword(s):  
Grain Size ◽  
Sheet Thickness ◽  
Specimen Size ◽  
Coarse Grained ◽  
Thick Sheet ◽  
Hardness Profile ◽  
Localized Deformation ◽  
Fine Grained ◽  
Deformation Distribution ◽  
Deformation Area

Sheet metal forming often consists of bending processes in which gradients of deformation exists through the thickness of the workpiece in a localized deformation area. In microscale bending, these deformation gradients become much steeper, as the changes in the deformation occur over short distances (in the order of micrometers). In addition, with miniaturization, the number of grains that are present through the thickness decreases significantly. In this research, the effect of grain size and specimen size on the deformation distribution through the thickness of microbent sheet specimens was investigated via microhardness evaluations. It was found that the deformation distribution, i.e., hardness profile, is not affected significantly by the grain size when the sheet thickness is large (for 1.625 mm specimens) or by miniaturization of the specimen size when the grain size is fine. However, the deformation distribution of the coarse grained specimens deviates from the fine grained ones and from the 1.625 mm thick sheet specimens when the specimen size is miniaturized.

scholarly journals Fabrication of nanoceramic hin-wall tubes by magnetic pulsed compaction and thermal sintering

2005 ◽  
Vol 37 (1) ◽  
pp. 55-60 ◽  
Author(s):  
V.V. Ivanov ◽  
S.Y. Ivin ◽  
V.R. Khrustov ◽  
Y.A. Kotov ◽  
A.M. Murzakaev ◽  
...  
Keyword(s):  
Grain Size ◽  
Wall Thickness ◽  
Thin Wall ◽  
Fine Grained ◽  
Mean Grain Size ◽  
Electrolytic Properties ◽  
Thermal Sintering

Gasproof thin-wall tubes of fine-grained ceramics based on zirconia and gadolinia have been produced by magnetic pulsed compaction and thermal sintering. Data on their structures and electric characteristics are presented. The tubes with a diameter of ~ 15 mm, wall thickness of ~ 0.7 mm, and length up to 80 mm are characterized by an uniform porous-free structure with a mean grain size in the range of 100 - 300 nm. The obtained ceramics possess high electrolytic properties.

scholarly journals Recrystallization of ice enhances the creep and vulnerability to fracture of ice shelves 

2021 ◽  
Author(s):  
Meghana Ranganathan ◽  
Brent Minchew ◽  
Colin Meyer ◽  
Matej Pec
Keyword(s):  
Grain Size ◽  
Ice Sheet ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Model Parameters ◽  
Localized Deformation ◽  
Ice Shelves ◽  
Fine Grained ◽  
Initiation And Propagation ◽  
Rapid Deformation

&lt;p&gt;The initiation and propagation of fractures in floating regions of Antarctica has the potential to destabilize large regions of the ice sheet, leading to significant sea-level rise. While observations have shown rapid, localized deformation and damage in the margins of fast-flowing glaciers, there remain gaps in our understanding of how rapid deformation affects the creep and toughness of ice. Here we derive a model for dynamic recrystallization in ice and other rocks that includes a novel representation of migration recrystallization, which is absent from existing models but is likely to be dominant in warm areas undergoing rapid deformation within the ice sheet. We show that, in regions of elevated strain rate, grain sizes in ice may be larger than expected (~15 mm) due to migration recrystallization, a significant deviation from solid earth studies which find fine-grained rock in shear zones. This may imply that ice in shear margins deforms primarily by dislocation creep, suggesting a flow-law exponent of n=4 in these regions. Further, we find from existing models that this increase in grain size results in a decrease in tensile strength of ice by ~75% in the margins of glaciers. Thus, we expect that this increase in grain size makes the margins of fast-flowing glaciers less viscous and more vulnerable to fracture than we may suppose from standard model parameters.&lt;/p&gt;

scholarly journals Mechanical Properties of Dye 3 Greenland Deep Ice Cores

1984 ◽  
Vol 5 ◽  
pp. 1-8 ◽  
Author(s):  
Nobuhiko Azuma ◽  
Akira Higashi
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Power Law ◽  
Ice Core ◽  
Ice Cores ◽  
Uniaxial Stress ◽  
Strain Rates ◽  
Compression Tests ◽  
Polycrystalline Ice ◽  
Relationship Of

Uniaxial compression tests were carried out with specimens cut from several deep ice cores obtained at Dye 3, Greenland, in 1980 and 1981. The power law relationship of = Αση was obtained between the uniaxial strain-rate and the uniaxial stress σ. In a range of strain-rates between 10−8 and 10−7 s−1, the value of the power n for samples with strong single maximum fabric was approximately 4, significantly larger than the value of 3 which has been generally accepted from experiments using artificial polycrystalline ice. A work-hardening effect was found in the ice-core samples taken from a depth of 1900 m, which had a smaller grain size than the others. Recrystallization occurred when the temperature of the specimen was raised during the test and this ultimately caused the formation of the so-called diamond pattern ice fabric.

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.

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