scholarly journals An analysis of compressive strain in adjacent temperature-gradient and equi-temperature layers in a natural snow cover

1980 ◽  
Vol 26 (94) ◽  
pp. 283-289 ◽  
Author(s):  
Richard L. Armstrong
Keyword(s):  
Strain Rate ◽  
Snow Cover ◽  
Compressive Strain ◽  
Coarse Grained ◽  
Adjacent Layer ◽  
Dominant Type ◽  
Fine Grained ◽  
Order Of Magnitude ◽  
Alpine Research ◽  
Natural Snow

AbstractCompressive strain-rates in discrete layers of a sub-alpine snow cover are analyzed. Individual layers are identified according to density and the dominant type of metamorphism which contributed to their formation. Data were collected during four winter seasons at the Institute of Arctic and Alpine Research (INSTAAR) snow-study site (3 400 m), Red Mountain Pass, south-western Colorado, U.S.A. At average densities of less than 250 kg m₋3the influence of metamorphism on strain-rate is not apparent. However, at densities greater than 250 kg m₋3, two separate relationships emerge for strain as a function of crystal type and density. While two adjacent layers may exhibit comparable densities, a layer of sintered, fine grained (ET) snow indicates a strain-rate approximately one order of magnitude greater than an adjacent layer of cohesionless, coarse-grained (TG) snow.

scholarly journals An analysis of compressive strain in adjacent temperature-gradient and equi-temperature layers in a natural snow cover

1980 ◽  
Vol 26 (94) ◽  
pp. 283-289 ◽  
Author(s):  
Richard L. Armstrong
Keyword(s):  
Strain Rate ◽  
Snow Cover ◽  
Compressive Strain ◽  
Coarse Grained ◽  
Adjacent Layer ◽  
Dominant Type ◽  
Fine Grained ◽  
Order Of Magnitude ◽  
Alpine Research ◽  
Natural Snow

AbstractCompressive strain-rates in discrete layers of a sub-alpine snow cover are analyzed. Individual layers are identified according to density and the dominant type of metamorphism which contributed to their formation. Data were collected during four winter seasons at the Institute of Arctic and Alpine Research (INSTAAR) snow-study site (3 400 m), Red Mountain Pass, south-western Colorado, U.S.A. At average densities of less than 250 kg m₋3 the influence of metamorphism on strain-rate is not apparent. However, at densities greater than 250 kg m₋3, two separate relationships emerge for strain as a function of crystal type and density. While two adjacent layers may exhibit comparable densities, a layer of sintered, fine grained (ET) snow indicates a strain-rate approximately one order of magnitude greater than an adjacent layer of cohesionless, coarse-grained (TG) snow.

Tensile Ductility of Ultra-Fine Grained Copper at High Strain Rate

2010 ◽  
Vol 160-162 ◽  
pp. 260-266 ◽  
Author(s):  
Tao Suo ◽  
Kui Xie ◽  
Yu Long Li ◽  
Feng Zhao ◽  
Qiong Deng
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Testing Machine ◽  
Coarse Grained ◽  
Dislocation Dynamic ◽  
Pressing Method ◽  
Fine Grained ◽  
Angular Pressing ◽  
Split Hopkinson

In this paper, ultra-fine grained copper fabricated by equal channel angular pressing method and annealed coarse grained copper were tensioned under both quasi-static and dynamic loading conditions using an electronic universal testing machine and the split Hopkinson tension bar respectively. The rapture surface of specimen was also observed via a Scanning Electron Microscope (SEM). The experimental results show that the ductility of polycrystalline copper decreases remarkably due to the grain refinement. However, with the increase of applied strain rate, ductility of the UFG-Cu is enhanced. The fracture morphologies also give the evidence of enhanced ductility of UFG-Cu at high strain rate. It is believed the enhanced ductility of UFG materials at high strain rate can be attributed to the restrained dislocation dynamic recovery.

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 Boudinage in Glacier Ice — Some Examples

1975 ◽  
Vol 14 (72) ◽  
pp. 383-393 ◽  
Author(s):  
M. J. Hambrey ◽  
A. G. Milnes
Keyword(s):  
Compressive Strain ◽  
Coarse Grained ◽  
Planar Anisotropy ◽  
Fine Grained ◽  
Or Groups ◽  
First Results ◽  
Glacier Ice ◽  
Strain Axis ◽  
The Difference ◽  
Shear Planes

Boudinage structures have only rarely been reported in glacier ice, yet they seem to be widespread in Swiss glaciers. They form in debris-free, strongly foliated ice by the stretching, necking and rupture of layers or groups of layers, when the principal compressive strain axis lies at a high angle to the layering. Two main types of boudinage are distinguished. The first results from the difference in competence between fine-grained and coarse-grained ice, and indicates that the former is more resistant to flow than the latter. The second occurs in more equigranular ice which shows a strong planar anisotropy; associated with the necking of such ice is the development of shear planes, along which the layers are displaced. As in deformed rocks, it is not possible to determine the directions of the finite principal strain axes from the boudinage structures alone. Although the boudins described here all occur in longitudinal foliation, it is suggested that they are likely to form in other situations also.

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.

Electrical conductivity of dry lower crustal rocks

Geophysics ◽  
1983 ◽  
Vol 48 (1) ◽  
pp. 52-61 ◽  
Author(s):  
K. A. Kariya ◽  
T. J. Shankland
Keyword(s):  
Electrical Conductivity ◽  
Coarse Grained ◽  
Mean Values ◽  
Crustal Rocks ◽  
Fine Grained ◽  
Rock Types ◽  
Order Of Magnitude ◽  
Temperature Ranges ◽  
Best Fitting ◽  
Lower Crustal

This study provides values of electrical conductivity of possible lower crustal materials to assist interpretation of lower crustal magnetotelluric soundings. We present mean values of conductivity measurements collected from the literature for dry mafic and silicic rocks in the temperature range of 500°C to 1000°C. We observe statistically significant differences between rock types: mafic rocks are better conductors than granites by about half an order of magnitude and within the mafic group, aphanitic (fine‐grained) rocks have higher conductivity than phaneritic (coarse‐grained) ones. “Best‐fitting” curves of log conductivity versus temperature are presented for each rock type to show mean log conductivity values together with standard deviations so that most probable temperature ranges can be inferred from conductivity. Because the laboratory rocks are dry, their conductivities are lower at a given temperature than they would be if fluids or volatiles were present; hence any temperatures inferred from magnetotelluric (MT) contivities are upper bounds.

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 Crystallization and Segregation of Syenite in Shallow Mafic Sills: Insights from the San Rafael Subvolcanic Field, Utah

2020 ◽  
Author(s):  
Aurelie Germa ◽  
Danielle Koebli ◽  
Paul Wetmore ◽  
Zachary Atlas ◽  
Austin Arias ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Mafic Magma ◽  
Coarse Grained ◽  
Geochemical Data ◽  
Fine Grained ◽  
Mantle Sources ◽  
Plumbing Systems ◽  
Order Of Magnitude ◽  
Magma Compositions ◽  
San Rafael

Abstract Exposed plumbing systems provide important insight into crystallization and differentiation in shallow sills beneath volcanic fields. We use whole rock major element, trace element and radiogenic isotopic compositions, along with mineral geochemical data on 125 samples to examine the conditions of melt differentiation in shallow sills from the exposed 4-Ma-old San Rafael subvolcanic field (SRVF), Utah. The field consists of ∼2000 dikes, 12 sills and 63 well preserved volcanic conduits. Intrusive rocks consist of mainly fine-grained trachybasalts and coarse-grained syenites, which are alkaline, comagmatic and enriched in Ba, Sr and LREE. Within sills, syenite is found as veins, lenses, and sheets totally enveloped by the basalt. The SRVF intrusions have geochemical signatures of both enriched sub-continental lithospheric and asthenospheric mantle sources. We estimate partial melting occurred between 1·2 and 1·9 GPa (50–70 km), with mantle potential temperatures in the range 1260–1326 ± 25°C, consistent with those estimated for volcanic rocks erupted on the Colorado Plateau. Geobarometry results based on clinopyroxene chemistry indicate that (1) basalt crystallized during ascent from at least 40 km deep with limited lithospheric storage, and (2) syenites crystallized only in the sills, ∼1 km below the surface. San Rafael mafic magma was emplaced in sills and started to crystallize inward from the sill margins. Densities of basalt and syenite at solidus temperatures are 2·6 and 2·4 g/cc, respectively, with similar viscosities of ∼150 Pa s. Petrographic observations and physical properties suggest that syenite can be physically separated from basalt by crystal compaction and segregation of the tephrophonolitic residual liquid out of the basaltic crystal mush after reaching 30–45% of crystallization. Each individual sill is 10–50 m thick and would have solidified fairly rapidly (1–30 years), the same order of magnitude as the duration of common monogenetic eruptions. Our estimates imply that differentiation in individual shallow sills may occur during the course of an eruption whose style may vary from effusive to explosive by tapping different magma compositions. Our study shows that basaltic magmas have the potential to differentiate to volatile-rich magma in shallow intrusive systems, which may increase explosivity.

scholarly journals Evaluation of Hot Workability of Powder Metallurgy Ni-Based Superalloy with Different Initial Microstructures

2020 ◽  
Vol 52 (1) ◽  
pp. 181-193
Author(s):  
Masaya Higashi ◽  
Naoya Kanno
Keyword(s):  
Grain Size ◽  
Powder Metallurgy ◽  
Strain Rate ◽  
Hot Isostatic Pressing ◽  
Hot Extrusion ◽  
Strain Rate Range ◽  
Coarse Grained ◽  
Hot Workability ◽  
Fine Grained ◽  
Nucleation Sites

AbstractThe effect of the initial microstructure on the hot workability of a powder metallurgy Ni-based superalloy was investigated in the high-temperature range of 950 °C to 1180 °C and strain rate range of 0.001 to 1.0 s−1. Six samples with different initial microstructures were fabricated by various hot isostatic pressing (HIP) conditions and subsequent treatments such as hot extrusion. The coarse-grained samples exhibited low hot workability regardless of the deformation conditions. In contrast, the hot workability of the fine-grained samples significantly varied depending on the deformation conditions. The hot workability exhibited a peak at the sub-solvus temperature of ~ 1100 °C and decreased at temperatures higher and lower than this temperature. In addition, the hot workability decreased monotonically with increasing the strain rate. The prior particle boundaries (PPBs) acted as cavity nucleation sites and crack paths, especially at lower temperatures and higher strain rates, resulting in early fracture and low hot workability. With decreasing the grain size, the hot workability at the peak temperature improved. The extruded sample with the smallest grain size exhibited the best hot workability, owing to the avoidance of PPB fracture and the acceleration of dynamic recrystallization.

The Dynamic Behavior of Ultra-Fine-Grained Copper Fabricated by Equal Channel Angular Pressing

2010 ◽  
Vol 667-669 ◽  
pp. 891-896
Author(s):  
Yue Cheng Dong ◽  
Igor V. Alexandrov ◽  
Jing Tao Wang
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Equal Channel Angular Pressing ◽  
High Strain ◽  
Maximum Yield ◽  
Coarse Grained ◽  
Static Compression ◽  
Fine Grained ◽  
Angular Pressing ◽  
High Strain Rate Deformation

The high-strain-rate response of ultra-fine-grained (UFG) copper fabricated by equal channel angular pressing (ECAP) has been characterized by Split Hopkinson Pressure Bar (SHPB) test and quasi-static compression test has also been performed for comparison here. In the result of quasi-static tests a maximum yield stress equal to 432 MPa has been reached, at the same time the corresponding value turned out to be 995 MPa after a dynamic loading with the strain rate equal to 1700 s-1. It has been demonstrated that the strain rate sensitivity coefficient (m) has enhanced from 0.026 (coarse-grained copper) to 0.037 (UFG copper). Microstructure has indicated a high dislocation density and deformation twins inside the grains formed after a high-strain-rate deformation, which resulted in a high flow stress. The occurrence of a dynamic recrystallization has also been observed in the UFG copper subjected to high-strain-rate deformation. This has become apparent as an accelerated thermal softening and inherent instability typical for the UFG structure. Absence of adiabatic shear bands pointed out that UFG copper can be subjected to a dynamic impact without any fracture.

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