A composite viscoelastic model for incorporating grain boundary sliding and transient diffusion creep; correlating creep and attenuation responses for materials with a fine grain size

2010 ◽  
Vol 90 (20) ◽  
pp. 2817-2840 ◽  
Author(s):  
Marshall Sundberg ◽  
Reid F. Cooper
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Viscoelastic Model ◽  
Grain Boundary Sliding ◽  
Diffusion Creep ◽  
Fine Grain ◽  
Transient Diffusion ◽  
Boundary Sliding

Strain localisation during diffusion creep: influence of grain coarsening and grain boundary sliding

2020 ◽  
Author(s):  
John Wheeler ◽  
Lynn Evans ◽  
Robyn Gardner ◽  
Sandra Piazolo
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Earth Pressure ◽  
Grain Boundary Sliding ◽  
Mechanical Anisotropy ◽  
Limited Attention ◽  
Diffusion Creep ◽  
Pressure Solution ◽  
Grain Coarsening ◽  
Boundary Sliding

<p>Diffusion creep and the wet low temperature version, pressure solution, are major deformation mechanisms in the Earth. Pressure solution operates in many metamorphosing systems in the crust and may contribute to slow creep on fault surfaces. Diffusion creep prevails in areas of the upper mantle deforming slowly, and possibly in most of the lower mantle. Both mechanisms contribute to localisation since small grain sizes can deform faster.</p><p>However, there has been limited attention paid to the evolution of microstructure during diffusion creep. In some experiments grains coarsen; in some but not all experiments grains remain rather equant. We have developed a grain-scale numerical model for diffusion creep, which indicates that those processes are very important in influencing evolving strength. Our models illustrate three behaviours.</p><ol><li>Strain localises along slip surfaces formed by aligned grain boundaries on all scales. This affects overall strength.</li> <li>Diffusion creep is predicted to produce elongate grains and then the overall aggregate has intense mechanical anisotropy. Thus strength during diffusion creep, and localisation on weak zones, is influenced not just by grain size but by other aspects of microstructure.</li> <li>Grain coarsening increases grain size and strength. Our most recent work shows how it interacts with ongoing deformation. In particular grain growth can lead to particular grain shapes which are directly related to strain rate, and influence strength. Consequently, understanding localisation during diffusion creep must encompass the effects of diffusion itself, grain boundary sliding and grain coarsening.</li> </ol>

scholarly journals Syn-shearing deformation mechanisms of minerals in partially molten metapelites

2021 ◽  
Author(s):  
Dripta Dutta ◽  
Santanu Misra ◽  
David Mainprice
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundary Sliding ◽  
Cylindrical Sample ◽  
Deformation Mechanisms ◽  
Axial Section ◽  
Fine Grain ◽  
Shearing Deformation ◽  
Boundary Sliding ◽  
Quartz Grains

We investigated an experimentally sheared (γ = 15, γ ̇ = 3 x 10-4s-1, 300 MPa, 750°C) quartz-muscovite aggregate to understand the deformation of parent and new crystals in partially molten rocks. The SEM and EBSD analyses along the longitudinal axial section of the cylindrical sample suggest that quartz and muscovite melted partially and later produced K-feldspar, ilmenite, biotite, mullite, and cordierite. Quartz grains became finer, and muscovite was almost entirely consumed in the process. With increasing , melt and crystal fractions decreased and increased, respectively. Amongst the new minerals, K-feldspar grains (highest area fraction and coarsest) nucleated first, whereas cordierite and mullite grains, finest and least in number, respectively, nucleated last. Fine grain size, weak CPOs, low intragranular deformation, and equant shapes suggest both initial and new minerals deformed dominantly by melt-assisted grain boundary sliding, which is further substantiated by higher misorientations between adjacent grains of quartz, K-feldspar, and ilmenite.

scholarly journals The role of grain size evolution in the rheology of ice: implications for reconciling laboratory creep data and the Glen flow law

2021 ◽  
Vol 15 (9) ◽  
pp. 4589-4605
Author(s):  
Mark D. Behn ◽  
David L. Goldsby ◽  
Greg Hirth
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Stress Exponent ◽  
Ice Sheets ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Ice Flow ◽  
Size Evolution ◽  
Boundary Sliding ◽  
Flow Law

Abstract. Viscous flow in ice is often described by the Glen flow law – a non-Newtonian, power-law relationship between stress and strain rate with a stress exponent n ∼ 3. The Glen law is attributed to grain-size-insensitive dislocation creep; however, laboratory and field studies demonstrate that deformation in ice can be strongly dependent on grain size. This has led to the hypothesis that at sufficiently low stresses, ice flow is controlled by grain boundary sliding, which explicitly incorporates the grain size dependence of ice rheology. Experimental studies find that neither dislocation creep (n ∼ 4) nor grain boundary sliding (n ∼ 1.8) have stress exponents that match the value of n ∼ 3 in the Glen law. Thus, although the Glen law provides an approximate description of ice flow in glaciers and ice sheets, its functional form is not explained by a single deformation mechanism. Here we seek to understand the origin of the n ∼ 3 dependence of the Glen law by using the “wattmeter” to model grain size evolution in ice. The wattmeter posits that grain size is controlled by a balance between the mechanical work required for grain growth and dynamic grain size reduction. Using the wattmeter, we calculate grain size evolution in two end-member cases: (1) a 1-D shear zone and (2) as a function of depth within an ice sheet. Calculated grain sizes match both laboratory data and ice core observations for the interior of ice sheets. Finally, we show that variations in grain size with deformation conditions result in an effective stress exponent intermediate between grain boundary sliding and dislocation creep, which is consistent with a value of n = 3 ± 0.5 over the range of strain rates found in most natural systems.

Mechanical Properties of Novel Nanocrystalline Materials

2001 ◽  
Author(s):  
J. Narayan ◽  
H. Wang ◽  
A. Kvit
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
High Surface ◽  
Grain Boundary Sliding ◽  
Boundary Shear ◽  
Functionally Gradient ◽  
Boundary Sliding ◽  
First Time ◽  
Critical Grain Size

Abstract We have synthesized nanocrystalline thin films of Cu, Zn, TiN, and WC having uniform grain size in the range of 5 to 100 nm. This was accomplished by introducing a couple of manolayers of materials with high surface and have a weak interaction with the substrate. The hardness measurements of these well-characterized specimens with controlled microstructures show that hardness initially increases with decreasing grain size following the well-known Hall-Petch relationship (H∝d−½). However, there is a critical grain size below which the hardness decreases with decreasing grain size. The experimental evidence for this softening of nanocrystalline materials at very small grain sizes (referred as reverse Hall-Petch effect) is presented for the first time. Most of the plastic deformation in our model is envisioned to be due to a large number of small “sliding events” associated with grain boundary shear or grain boundary sliding. This grain-size dependence of hardness can be used to create functionally gradient materials for improved adhesion and wear among other improved properties.

scholarly journals Hierarchical creep cavity formation in an ultramylonite and implications for phase mixing

Solid Earth ◽  
2017 ◽  
Vol 8 (6) ◽  
pp. 1193-1209 ◽  
Author(s):  
James Gilgannon ◽  
Florian Fusseis ◽  
Luca Menegon ◽  
Klaus Regenauer-Lieb ◽  
Jim Buckman
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Finite Strain ◽  
Grain Boundary Sliding ◽  
Large Strains ◽  
Cavity Formation ◽  
Phase Mixing ◽  
Transient Phenomena ◽  
Boundary Sliding

Abstract. Establishing models for the formation of well-mixed polyphase domains in ultramylonites is difficult because the effects of large strains and thermo-hydro-chemo-mechanical feedbacks can obscure the transient phenomena that may be responsible for domain production. We use scanning electron microscopy and nanotomography to offer critical insights into how the microstructure of a highly deformed quartzo-feldspathic ultramylonite evolved. The dispersal of monomineralic quartz domains in the ultramylonite is interpreted to be the result of the emergence of synkinematic pores, called creep cavities. The cavities can be considered the product of two distinct mechanisms that formed hierarchically: Zener–Stroh cracking and viscous grain-boundary sliding. In initially thick and coherent quartz ribbons deforming by grain-size-insensitive creep, cavities were generated by the Zener–Stroh mechanism on grain boundaries aligned with the YZ plane of finite strain. The opening of creep cavities promoted the ingress of fluids to sites of low stress. The local addition of a fluid lowered the adhesion and cohesion of grain boundaries and promoted viscous grain-boundary sliding. With the increased contribution of viscous grain-boundary sliding, a second population of cavities formed to accommodate strain incompatibilities. Ultimately, the emergence of creep cavities is interpreted to be responsible for the transition of quartz domains from a grain-size-insensitive to a grain-size-sensitive rheology.

scholarly journals Myrmekite and strain weakening in granitoid mylonites

2018 ◽  
Author(s):  
Alberto Ceccato ◽  
Luca Menegon ◽  
Giorgio Pennacchioni ◽  
Luiz Fernando Grafulha Morales
Keyword(s):  
Grain Size ◽  
Heterogeneous Nucleation ◽  
Eastern Alps ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Diffusion Creep ◽  
Phase Mixing ◽  
Fine Grained ◽  
Fine Grain ◽  
Creep Cavitation

Abstract. At mid-crustal conditions, deformation of feldspar is mainly accomplished by a combination of fracturing, dissolution/precipitation and reaction-weakening mechanisms. In particular, K-feldspar is reaction-weakened by formation of strain-induced myrmekite – a fine-grained symplectite of plagioclase and quartz. Here we investigate with EBSD the microstructure of a granodiorite mylonite, developed at 420–460 °C during cooling of the Rieserferner pluton (Eastern Alps), to assess the microstructural processes and the role of weakening associated with myrmekite development. Our analysis shows that the crystallographic orientation of the plagioclase of pristine myrmekite was controlled by that of the replaced K-feldspar. Myrmekite nucleation resulted in both grain size reduction and ordered phase mixing by heterogeneous nucleation of quartz and plagioclase. The fine grain size of sheared myrmekite promoted grain size-sensitive creep mechanisms including fluid-assisted grain boundary sliding in plagioclase, coupled with heterogeneous nucleation of quartz within creep cavitation pores. Flow laws calculated for monomineralic quartz, feldspar, and quartz + plagioclase aggregates (sheared myrmekite), show that during mylonitization at 450 °C, grain-size-sensitive creep in sheared myrmekite accommodated strain rates several orders of magnitude higher than monomineralic quartz layers deforming by dislocation creep. Therefore, diffusion creep and grain size-sensitive processes contributed significantly to bulk rock weakening during mylonitization. Our results have implications for modelling the rheology of the mid-upper continental (felsic) crust.

Comments on grain-boundary sliding in diffusion creep

1976 ◽  
Vol 10 (2) ◽  
pp. 161-162
Author(s):  
E.H. Aigeltinger ◽  
R.C. Gifkins
Keyword(s):  
Grain Boundary ◽  
Grain Boundary Sliding ◽  
Diffusion Creep ◽  
Boundary Sliding
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