scholarly journals Theoretical derivation of flow laws for quartz dislocation creep: Comparisons with experimental creep data and extrapolation to natural conditions using water fugacity corrections

2017 ◽  
Vol 122 (8) ◽  
pp. 5956-5971 ◽  
Author(s):  
Jun-ichi Fukuda ◽  
Ichiko Shimizu
Keyword(s):  
Dislocation Creep ◽  
Creep Data ◽  
Natural Conditions ◽  
Theoretical Derivation ◽  
Experimental Creep ◽  
Water Fugacity ◽  
Flow Laws

Tunable Membrane for Electromagnetic Devices Using Dielectric Elastomers

2008 ◽  
Vol 61 ◽  
pp. 141-146
Author(s):  
Christian Bolzmacher ◽  
Karin Bauer ◽  
Ulrich Schmid ◽  
Helmut Seidel ◽  
Moustapha Hafez
Keyword(s):  
Material Model ◽  
Silicone Membrane ◽  
Creep Data ◽  
Electromagnetic Actuators ◽  
Membrane Behavior ◽  
Electromagnetic Devices ◽  
Dynamic Experiments ◽  
Experimental Creep ◽  
Strain Relationship ◽  
Tunable Stiffness

The amplitudes of miniaturized electromagnetic actuators are clearly enhanced if the eigenfrequencies of the membrane are used for actuation. However, the bandwidth for such operation is very limited. This can be overcome to some extent by the employment of membranes with electrically tunable stiffness. In this context we investigated membranes of dielectric elastomer materials and present experimental results on the ability to change their pre-strain to shift the eigenmodes to lower frequencies upon activation. Furthermore, the viscoelastic properties of an acrylic and a silicone membrane are investigated and compared to dynamic experiments. The parameters for the stiffness and viscoelasticity are derived from the experimental creep data and incorporated in a hyperelastic material model. Using this adapted stress-strain relationship the membrane behavior over time can be evaluated for different loading as well as pre-strain conditions.

scholarly journals Nanoindentation Studies of Plasticity and Dislocation Creep in Halite

Geosciences ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 79 ◽  
Author(s):  
Christopher Thom ◽  
David Goldsby
Keyword(s):  
Strain Rate ◽  
Stress Exponent ◽  
Creep Behavior ◽  
Constant Load ◽  
Dislocation Creep ◽  
Indentation Creep ◽  
Creep Tests ◽  
Creep Flow ◽  
A Value ◽  
Flow Laws

Previous deformation experiments on halite have collectively explored different creep mechanisms, including dislocation creep and pressure solution. Here, we use an alternative to conventional uniaxial or triaxial deformation experiments—nanoindentation tests—to measure the hardness and creep behavior of single crystals of halite at room temperature. The hardness tests reveal two key phenomena: (1) strain rate-dependent hardness characterized by a value of the stress exponent of ~25, and (2) an indentation size effect, whereby hardness decreases with increasing size of the indents. Indentation creep tests were performed for hold times ranging from 3600 to 106 s, with a constant load of 100 mN. For hold times longer than 3 × 104 s, a transition from plasticity to power-law creep is observed as the stress decreases during the hold, with the latter characterized by a value of the stress exponent of 4.87 ± 0.91. An existing theoretical analysis allows us to directly compare our indentation creep data with dislocation creep flow laws for halite derived from triaxial experiments on polycrystalline samples. Using this analysis, we show an excellent agreement between our data and the flow laws, with the strain rate at a given stress varying by less than 5% for a commonly used flow law. Our results underscore the utility of using nanoindentation as an alternative to more conventional methods to measure the creep behavior of geological materials.

scholarly journals Experimental grain growth of quartz aggregates under wet conditions and its application to deformation in nature

Solid Earth ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 621-636 ◽  
Author(s):  
Junichi Fukuda ◽  
Hugues Raimbourg ◽  
Ichiko Shimizu ◽  
Kai Neufeld ◽  
Holger Stünitz
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Growth Parameters ◽  
Growth Exponent ◽  
High Porosity ◽  
Natural Conditions ◽  
Grain Sizes ◽  
Growth Laws ◽  
Water Fugacity ◽  
Quartz Aggregates

Abstract. Grain growth of quartz was investigated using two quartz samples (powder and novaculite) with water under pressure and temperature conditions of 1.0–2.5 GPa and 800–1100 ∘C. The compacted powder preserved a substantial porosity, which caused a slower grain growth than in the novaculite. We assumed a grain growth law of dn-d0n=k0fH2Orexp⁡(-Q/RT)t with grain size d (µm) at time t (seconds), initial grain size d0 (µm), growth exponent n, a constant k0 (µmn MPa−r s−1), water fugacity fH2O (MPa) with the exponent r, activation energy Q (kJ mol−1), gas constant R, and temperature T in Kelvin. The parameters we obtained were n=2.5±0.4, k0=10-8.8±1.4, r=2.3±0.3, and Q=48±34 for the powder and n=2.9±0.4, k0=10-5.8±2.0, r=1.9±0.3, and Q=60±49 for the novaculite. The grain growth parameters obtained for the powder may be of limited use because of the high porosity of the powder with respect to crystalline rocks (novaculite), even if the differences between powder and novaculite vanish when grain sizes reach ∼70 µm. Extrapolation of the grain growth laws to natural conditions indicates that the contribution of grain growth to plastic deformation in the middle crust may be small. However, grain growth might become important for deformation in the lower crust when the strain rate is < 10−12 s−1.

Dynamic Recrystallization of Dense Polycrystalline NaCl: Dependence of Grain Size Distribution on Stress and Temperature

2004 ◽  
Vol 467-470 ◽  
pp. 1187-1192 ◽  
Author(s):  
J.H. ter Heege ◽  
J.H.P. de Bresser ◽  
C.J. Spiers
Keyword(s):  
Grain Size ◽  
Dynamic Recrystallization ◽  
Boundary Migration ◽  
Elevated Pressure ◽  
Dislocation Creep ◽  
Grain Boundary Migration ◽  
Subgrain Rotation ◽  
Recrystallized Grain Size ◽  
Flow Laws ◽  
Size Data

Only few models explain the development of a steady state grain size during dynamic recrystallization, and their microphysical basis is poorly understood. In this study, we investigate mechanical and microstructural data on dry and wet NaCl, deformed at a range of stresses and temperatures at elevated pressure, with the aim to evaluate the different models. The results show that dry NaCl continuously work hardens and shows evidence for recrystallization dominated by progressive subgrain rotation, while the wet material shows, at similar conditions, oscillating stressstrain behaviour and recrystallization dominated by grain boundary migration. Taking into account the distribution of grain size, deformation of wet NaCl is best described by flow laws based on composite grain size sensitive (GSS) solution-precipitation creep and grain size insensitive (GSI) dislocation creep. The recrystallized grain size data in wet NaCl can be modeled with the hypothesis that recrystallized grain size organises itself in the boundary between the GSS and GSS creep domains.

scholarly journals The effect of rock particles and D 2 O replacement on the flow behaviour of ice

2017 ◽  
Vol 375 (2086) ◽  
pp. 20150349 ◽  
Author(s):  
Ceri A. Middleton ◽  
Peter M. Grindrod ◽  
Peter R. Sammonds
Keyword(s):  
Confining Pressure ◽  
Dislocation Creep ◽  
Gradual Transition ◽  
Strain Rates ◽  
Natural Processes ◽  
Planetary Environments ◽  
Through Flow ◽  
Derived Properties ◽  
Equivalent Conditions ◽  
Flow Laws

Ice–rock mixtures are found in a range of natural terrestrial and planetary environments. To understand how flow processes occur in these environments, laboratory-derived properties can be extrapolated to natural conditions through flow laws. Here, deformation experiments have been carried out on polycrystalline samples of pure ice, ice–rock and D 2 O-ice–rock mixtures at temperatures of 263, 253 and 233 K, confining pressure of 0 and 48 MPa, rock fraction of 0–50 vol.% and strain-rates of 5 × 10 −7 to 5 × 10 −5  s −1 . Both the presence of rock particles and replacement of H 2 O by D 2 O increase bulk strength. Calculated flow law parameters for ice and H 2 O-ice–rock are similar to literature values at equivalent conditions, except for the value of the rock fraction exponent, here found to be 1. D 2 O samples are 1.8 times stronger than H 2 O samples, probably due to the higher mass of deuterons when compared with protons. A gradual transition between dislocation creep and grain-size-sensitive deformation at the lowest strain-rates in ice and ice–rock samples is suggested. These results demonstrate that flow laws can be found to describe ice–rock behaviour, and should be used in modelling of natural processes, but that further work is required to constrain parameters and mechanisms for the observed strength enhancement. This article is part of the themed issue ‘Microdynamics of ice’.

scholarly journals Pressure Dependence of Magnesite Creep

Geosciences ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 420
Author(s):  
Joseph W. Millard ◽  
Caleb W. Holyoke ◽  
Rachel K. Wells ◽  
Cole Blasko ◽  
Andreas K. Kronenberg ◽  
...  
Keyword(s):  
Oceanic Lithosphere ◽  
Coarse Grained ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Flow Strength ◽  
Dislocation Glide ◽  
Fine Grained ◽  
Grain Sizes ◽  
And Diffusion ◽  
Flow Laws

We determined the activation volumes (V*) for polycrystalline magnesite with grain sizes of 2 and 80 µm deforming by low temperature plasticity (LTP) mechanisms (kinking and dislocation glide), diffusion creep, and dislocation creep at temperatures of 500, 750, and 900 °C, respectively, and a strain rate of 1–2 × 10−5 s−1 at effective pressures of 2.9–7.5 GPa in a D-DIA and 0.76 GPa in a Griggs apparatus. In each set of experiments performed at a given temperature, the strength of magnesite increases with increasing pressure. Microstructures of fine-grained magnesite deformed at 500 °C and 750 °C are consistent with deformation by LTP mechanisms and diffusion creep, respectively. Microstructures of coarse-grained magnesite deformed at 900 °C are consistent with deformation by dislocation creep. Pressure dependencies of magnesite flow laws for LTP, diffusion creep, and dislocation creep are given by activation volumes of 34 (± 7), 2 (± 1), and 10 (± 5) × 10−6 m3/mol, respectively. Addition of these activation volumes to previously determined flow laws predicts magnesite strength to be much lower than the flow strength of olivine at all subduction zone depths of the upper mantle. Thus, subducting oceanic lithosphere that has been partially carbonated by reaction with CO2-bearing fluids may deform at lowered stresses where magnesite is present, possibly resulting in strain localization and unstable run-away shear.

scholarly journals Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earth’s upper mantle

2015 ◽  
Vol 1 (9) ◽  
pp. e1500360 ◽  
Author(s):  
Tomohiro Ohuchi ◽  
Takaaki Kawazoe ◽  
Yuji Higo ◽  
Ken-ichi Funakoshi ◽  
Akio Suzuki ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Upper Mantle ◽  
Laboratory Data ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Softening Effect ◽  
Water Fugacity ◽  
Boundary Sliding

Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth’s upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 1019.6to 1020.7Pa·s throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size–sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle.

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