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Simple Shear (simple + shear)

Distribution by Scientific Domains
Earth and Environmental Science37%

Terms modified by Simple Shear

  • simple shear flow
    		•

    Selected Abstracts

    The preservation of seismic anisotropy in the Earth's mantle during diffusion creep

    GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2009
    J. Wheeler
    SUMMARY Seismic anisotropy in the Earth, particularly in the mantle, is commonly interpreted as the result of solid-state deformation by dislocation creep that induces a lattice preferred orientation (LPO). Diffusion creep operates where stress levels are lower and/or grain sizes smaller. It is often assumed that diffusion creep induces grain rotations that eventually destroy any existing LPO. A new numerical test of this assumption shows that it is not necessarily the case: diffusion creep will create some relative grain rotations, but rotation rates decrease through time. Hence, when microstructural change due to diffusion creep dominates that due to grain growth, defined here as ,type P' behaviour (the converse being ,type O' behaviour), the model indicates that LPO will be weakened but preserved (for a variety of strain paths including both pure and simple shear). One measure of anisotropy is the proportional difference in shear wave velocities for different polarization vectors (AVs). A model olivine microstructure with equant grains and initial maximum AVs of 10.0 percent has this value reduced to 6.7 per cent when ,rotational steady state' is attained. Other models with different initial maximum AVs values exhibit final maximum AVs values more than half the initial values. If the grains are initially elongate by a factor of 2, maximum AVs is reduced just slightly, to 8.5 per cent. Thus, when grain growth plays a subordinate role to the deformation, diffusion creep weakens seismic anisotropy by a factor of less than 2 (using maximum AVs as a measure and olivine as an example). Consequently, the link between seismic anisotropy and deformation mechanism in the mantle requires reappraisal: regions with LPO may comprise material which once deformed by dislocation creep, but is now deforming by diffusion creep in a rotational steady state. [source]

    Mechanics of land subsidence due to groundwater pumping

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2010
    Muniram Budhu
    Abstract This paper presents the formulation of the basic mechanics governing the changes in stress states from groundwater pumping and comparisons among predicted land subsidence from this mechanics with existing analyses and field data. Land subsidence is a growing, global problem caused by petroleum and groundwater withdrawal, mining operations, natural settlement, hydro-compaction, settlement of collapsible soils, settlement of organic soils and sinkholes. This paper is concerned with the land subsidence due to groundwater level decline by groundwater pumping. It is shown that the stress state consists of asymmetric stresses that are best simulated by a Cosserat rather than a Cauchy continuum. Land subsidence from groundwater level decline consists of vertical compression (consolidation), shear displacement and macro-rotation. The latter occurs when conditions are favorable (e.g. at a vertical interface) for the micro-rotation imposed by asymmetric stresses to become macro-rotation. When the length of the cone of depression is beyond ,2 times the thickness of the aquifer, simple shear on vertical planes with rotation is the predominant deformation mode. Otherwise, simple shear on horizontal planes is present. The predicted subsidence using the mechanics developed in this paper compares well with data from satellite-borne interferometric synthetic aperture radar. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Numerical simulations of simple shear with non-coaxial soil models

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2006
    Yunming Yang
    Abstract This paper investigates the effects of a non-coaxial model on simulated stress,strain behaviour of granular materials subject to simple shearing under various initial conditions. In most cases, a significant difference of predictions between coaxial and non-coaxial modelling is found during the early stage in shearing. With the increase in shearing, non-coaxial simulations approach and tend to coincide with coaxial simulations. It is also found that the roles of non-coaxial modelling in simulating simple shear behaviour are considerably influenced by hardening rules, flow rules, initial static lateral pressure coefficients. In some cases, the non-coaxial modelling gives a similar simulation as the coaxial modelling. In other cases, the non-coaxial modelling decreases the hardening response or softening response of materials, compared with the coaxial modelling. Under certain conditions, the predicted peak strength of materials with non-coaxial modelling is larger than that for coaxial modelling. Some of these observations can be attributed to the amount of principal stress rotation in various cases analysed. Others can be attributed to the difference between the directions of the non-coaxial plastic flow and those for coaxial plastic flow. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Evolution of a crustal-scale transpressive shear zone in the Albany,Fraser Orogen, SW Australia: 2.

    JOURNAL OF METAMORPHIC GEOLOGY, Issue 8 2004
    Mawson cratons, Tectonic history of the Coramup Gneiss, a kinematic framework for Mesoproterozoic collision of the West Australian
    Abstract Within the Albany,Fraser Orogen of southwestern Australia, the Coramup Gneiss is a NE,SW trending zone of high-strain rocks that preserves a detailed record of orogenesis related to Mesoproterozoic convergence of the West Australian and Mawson cratons. New structural, metamorphic and U,Pb SHRIMP zircon age data establish that the Coramup Gneiss underwent high-grade tectonism during both Stage I (c. 1290 Ma) and Stage II (c. 1170 Ma) of the Albany,Fraser Orogeny. Stage I commenced with c. 1300 Ma high- T, low- P M1a metamorphism during extension, and the formation of small-scale ptygmatic folds within a subhorizontal S1a gneissosity. High- P M1b metamorphism at c. 1290 Ma was accompanied by the transposition and shearing of S1a into a composite, shallow SE-dipping S1b foliation, and the development of tight recumbent F1b folds with S1-parallel axial surfaces and asymmetries indicating NW-directed thrusting. The preservation of a similar P,T,time record in the Fraser Complex (NE of the Coramup Gneiss) is consistent with large-scale, NW-directed Stage I thrusting of the Mawson Craton margin over the south-eastern edge of the West Australian Craton. Stage II tectonism in the western Coramup Gneiss involved high- T, low- P M2a metamorphism and the formation of subvertical SE-dipping D2 shear zones, shallow SW-plunging L2 mineral stretching lineations, and NW-verging F2 folds with S2-parallel axial surfaces. A synkinematic pegmatite dyke emplaced into a D2 shear zone yielded a U,Pb SHRIMP zircon age of 1168 ± 12 Ma. Kinematic indicators suggest a combination of pure shear flattening perpendicular to S2, and dextral simple shear. However, contemporaneous structures elsewhere in the Albany,Fraser Orogen are consistent with continued NW,SE convergence at craton-scale during Stage II, and oblique compression in the Coramup Gneiss is attributed to the arcuate geometry of the orogen-scale deformation front. [source]

    Design modifications to SMX static mixer for improving mixing

    AICHE JOURNAL, Issue 1 2006
    Shiping Liu
    Abstract Laminar mixing in SMX static mixers and the effect of geometry on mixing are studied using computational fluid dynamics. A frame-indifferent parameter is used to classify the flow types in the SMX mixer. All three typical flows (simple shear, pure elongation, and squeezing) appear within the flow field of the SMX mixer. The strain rate distribution in the SMX mixer is observed to be very nonuniform. A mixing element with 10 crossbars shows the best mixing quality, followed closely by the standard SMX mixing element with eight crossbars. The improved designs of the mixing element increase the average and peak strain rate, and provide a more uniform strain rate distribution and faster mixing rate compared to those of the standard SMX mixer. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source]

    Deformation styles as a key for interpreting glacial depositional environments

    JOURNAL OF QUATERNARY SCIENCE, Issue 6 2003
    Danny McCarroll
    Abstract Lithostratigraphical and lithofacies approaches used to interpret glacial sediments often ignore deformation structures that can provide the key to environment of formation. We propose a classification of deformation styles based on the geometry of structures rather than inferred environment of formation. Five styles are recognised: pure shear (P), simple shear (S), compressional (C), vertical (V) and undeformed (U). These dictate the first letter of the codes; the remaining letters conveying the evidence. This information can be used to reconstruct palaeostress fields and to infer physical properties of sediments when they deformed. Individual structures are not diagnostic of particular environments but the suite of structures, their relative scale, stratigraphical relationships, and orientation relative to palaeoslopes and to palaeoice-flow directions can be used to infer the environment in which they formed. This scheme is applied at five sites in west Wales. The typical succession is interpreted as subglacial sediments overlain by meltout tills, flow tills and sediment flows. Paraglacial redistribution of glacial sediments is widespread. Large-scale compressional deformation is restricted to sites where glaciers readvanced. Large-scale vertical deformation occurs where water was locally ponded near the ice margin. There is no evidence for glaciomarine conditions. Copyright © 2003 John Wiley & Sons, Ltd. [source]

    Linear and nonlinear melt-state viscoelastic properties of polypropylene/organoclay nanocomposites

    POLYMER ENGINEERING & SCIENCE, Issue 7 2008
    Ehssan Nazockdast
    Rheological behavior of polypropylene (PP)/organoclay nanocomposites varying in compatibilizer (PP- g -MA) and organoclay concentration was investigated. The samples were prepared by melt intercalation method in an internal mixer. The wide angle X-ray diffraction patterns and results of rheological measurements showed that the compatibilizer had strong influence in increasing the interlayer spacing. The observed low frequency liquid-like to solid-like transition and apparent yield stress in simple shear flows, along with convergence of transient shear stress to nonzero values in stress relaxation after the cessation of flow experiments, were found to be consistent with formation of a physical network in quiescent conditions which could be easily ruptured with applying low shear rates. The values of stress overshoot strain in flow reversal experiments were independent of shear rate, organoclay, and compatibilizer content. From the results of frequency sweep experiments in different nonlinear strain amplitudes it was shown that extended Cox-Merz analogy was valid in nonlinear dynamic deformations while the shear viscosity showed positive deviation from this analogy with higher deviations at lower shear rates. Results of storage modulus recovery and flow reversal experiments at different shear rates suggested that network structure is reformed with a much slower rate compared to the rotational relaxation of organoclay platelets. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers [source]

    Application of General Shear Theory to the Study of Formation Mechanism of the Metamorphic Core Complex: A Case Study of Xiaoqinling in Central China

    ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2000
    ZHANG Jinjiang
    Abstract: The kinematic vorticity number and strain of the mylonitic zone related to the detachment fault increase from ESE to WNW along the moving direction of the upper plate of the Xiaoqinling metamorphic core complex (XMCC) and the geometry of quartz c -axis fabrics changes progressively from crossed girdles to single girdles in the same direction. Therefore, pure shear is dominant in the ESE part of the XMCC while simple shear becomes increasingly important towards WNW. However, the shear type does not change with the strain across the shear zone, thus the variation of shear type is of significance in indicating the formation mechanism. The granitic plutons within the XMCC came from the deep source and their emplacement was an active and forceful upwelling prior to the detachment faulting. The PTt path demonstrates that magmatism is an important cause for the formation of the XMCC. The formation mechanism of the XMCC is supposed to be active plutonism and passive detachment. Crustal thickening and magmatic doming caused necking extension with pure shear, and magmatic heating and doming resulted in detachment extension with simple shear and formed the XMCC. [source]