scholarly journals Crevasse initiation and history within the McMurdo Shear Zone, Antarctica

2019 ◽  
Vol 65 (254) ◽  
pp. 989-999 ◽  
Author(s):  
Lynn Kaluzienski ◽  
Peter Koons ◽  
Ellyn Enderlin ◽  
Gordon Hamilton ◽  
Zoe Courville ◽  
...  
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Shear Zone ◽  
Large Scale ◽  
Radar Data ◽  
Small Scale ◽  
Shear Strain Rate ◽  
Surface Shear ◽  
Study Region ◽  
In Situ Data

AbstractWhile large-scale observations of intensified fracture and rifting can be observed through remote-sensing observations, understanding crevasse initiation may best be achieved with small-scale observations in which crevasses can be directly observed. Here we investigate the kinematic drivers of crevasse initiation in the McMurdo Shear Zone (MSZ), Antarctica. We delineated 420 crevasses from ~95 km of 400 MHz frequency ground-penetrating radar data and compared these data with kinematic outputs derived from remotely-sensed ice surface velocities to develop a statistical method to estimate crevasse initiation threshold strain rate values. We found the MSZ to be dominated by simple shear and that surface shear strain rates proved best for predicting crevasse features, with regions of higher shear strain rate more likely to have a greater number of crevasses. In the surveyed portion of our study region, values of shear strain rate and vorticity rate derived from the MEaSUREs2 velocity dataset range between 0.005–0.020 and 0.006–0.022 a−1, respectively, with crevasses located at ≥0.011 and ≥0.013 a−1. While threshold values from this study cannot be directly applied to other glacial environments, the method described here should allow for the study of shear margin evolution and assessment of localized damage and weakening processes in other locations where in situ data are available.

Modified Primary Shear Zone Analysis for Identification of Material Mechanical Behavior During Machining Process Using Genetic Algorithm

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
L. Pang ◽  
H. A. Kishawy
Keyword(s):  
Genetic Algorithm ◽  
Boundary Conditions ◽  
Strain Rate ◽  
Shear Strain ◽  
Shear Zone ◽  
Metal Cutting ◽  
Chip Thickness ◽  
Machining Process ◽  
Zone Model ◽  
Shear Strain Rate

In the current work, an inverse analysis on the primary shear zone was introduced to determine the five constants in Johnson–Cook’s material constitutive equation under the conditions of metal cutting. Based on the detailed analysis on the boundary conditions of the velocity and shear strain rate fields, Oxley’s “equidistant parallel-sided” shear zone model was revisited. A more realistic nonlinear shear strain rate distribution has been proposed under the frame of nonequidistant primary shear zone configuration, so that all the boundary conditions can be satisfied. Based on the presented analysis, the shear strain, shear strain rate and temperature at the main shear plane were calculated. In conjugation with the measured cutting forces and chip thickness, a genetic algorithm (GA) based optimization program has been developed for the system identification. In order to verify the effectiveness of the developed algorithm, the obtained material constants were used in a forward analytical simulation. The acceptable agreement with experimental data validates the proposed method.

High shear strain rate rheometry of polymer melts

2009 ◽  
Vol 114 (2) ◽  
pp. 864-873 ◽  
Author(s):  
A. L. Kelly ◽  
T. Gough ◽  
B. R. Whiteside ◽  
P. D. Coates
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Polymer Melts ◽  
Shear Strain Rate ◽  
High Shear

Rheology of colloids

Surfactants ◽  
2019 ◽  
pp. 400-424
Author(s):  
Bob Aveyard
Keyword(s):  
Strain Rate ◽  
Shear Strain ◽  
Shear Thickening ◽  
Rheological Behaviour ◽  
Maxwell Model ◽  
Colloidal Dispersions ◽  
Shear Strain Rate ◽  
Plastic Behaviour ◽  
Shear Thickening Fluids ◽  
External Forces

Lyophobic colloidal dispersions, aggregated surfactant systems, and polymer solutions, as well as foams and emulsions, can all be deformed by weak external forces; rheology is the study of deformation and flow of materials. Various rheological quantities arising from the response of a material to shear are defined. For liquids the stress, τ‎, applied is related to the rate of deformation, that is, the shear strain rate, γ̇. For Newtonian fluids τ‎ and γ̇ are linearly related and τ‎ / γ̇ is the viscosity, η‎. Other nonlinear relationships correspond to shear thinning and shear thickening fluids and to plastic behaviour in which there is a yield stress. Viscoelastic systems exhibit both viscous and elastic properties; such behaviour is often treated using the simple Maxwell model. Some illustrative experimentally observed rheological behaviour is presented.

scholarly journals Erebus Glacier Tongue, Mcmurdo Sound, Antarctica

1974 ◽  
Vol 13 (67) ◽  
pp. 27-35 ◽  
Author(s):  
G. Holdsworth
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Shear Strain ◽  
Longitudinal Strain ◽  
Strain Rates ◽  
Shear Strain Rate ◽  
Mcmurdo Sound ◽  
Glacier Tongue ◽  
The Past ◽  
Image Position

Examination of the past and present behaviour of the Erebus Glacier tongue over the last 60 years indicates that a major calving from the tongue appears to be imminent. Calculations of the regime of the tongue indicate that bottom melt rates may exceed 1 m a−1. By successive mapping of the ice tongue between the years 1947 and 1970, longitudinal strain-rates were determined using the change in distance between a set of 15 teeth, which are a prominent marginal feature of the tongue. Assuming a flow law for ice of the form where τ is the effective shear stress and is the effective shear strain-rate, values of the exponent n = 3 and B = 1 × 108 N m−2 are determined. These are in fair agreement with published values.

scholarly journals Deformation in the Vicinity of Ice Divides

1983 ◽  
Vol 29 (103) ◽  
pp. 357-373 ◽  
Author(s):  
Charles F. Raymond
Keyword(s):  
Finite Elements ◽  
Laminar Flow ◽  
Velocity Profile ◽  
Strain Rate ◽  
Shear Strain ◽  
Vertical Velocity ◽  
Flow Theory ◽  
Numerical Calculations ◽  
Shear Strain Rate ◽  
Horizontal Shear

AbstractNumerical calculations by finite elements show that the variation of horizontal velocity with depth in the vicinity of a symmetric, isothermal, non-slipping ice ridge deforming on a flat bed is approximately consistent with prediction from laminar flow theory except in a zone within about four ice thicknesses of the divide. Within this near-divide zone horizontal shear strain-rate is less concentrated near the bottom and downward velocity is less rapid in comparison to the flanks. The profiles over depth of horizontal and vertical velocity approach being linear and parabolic respectively. Calculations for various surface elevation profiles show these velocity profile shapes are insensitive to the ice-sheet geometry.

scholarly journals The theory of plane plastic strain for anisotropic metals

1949 ◽  
Vol 198 (1054) ◽  
pp. 428-437 ◽  
Keyword(s):  
Plastic Strain ◽  
Strain Rate ◽  
Shear Strain ◽  
Plane Strain ◽  
Yield Criterion ◽  
Elliptic Functions ◽  
Shear Strain Rate ◽  
Maximum Shear Strain ◽  
Geometrical Properties ◽  
Plane Plastic

A yield criterion and plastic stress-strain relations are formulated for anisotropic metals deformed under conditions of plane strain. The equations are shown to be hyperbolic, the characteristics coinciding with the directions of maximum shear strain-rate. When the anisotropy is uniformly distributed, the variation of the stresses along the characteristics is expressed in terms of elliptic functions, and geometrical properties of the field of characteristics are established. The theory is applied to the problem of indentation by a flat die.

scholarly journals Ice Flow Along AN Iagp Flow Line, Wilkes Land, Antarctica (Abstract only)

1982 ◽  
Vol 3 ◽  
pp. 346 ◽  
Author(s):  
N.W. Young ◽  
D. SheehY ◽  
T. Hamley
Keyword(s):  
Strain Rate ◽  
Large Scale ◽  
Flow Line ◽  
Accumulation Rate ◽  
Surface Profile ◽  
Ice Thickness ◽  
Shear Strain Rate ◽  
Surface Slope ◽  
Ice Flow ◽  
Wilkes Land

Trilateration and single line surveys have been made to about 900 km inland of Casey, Wilkes Land, to measure surface elevation, ice thickness, horizontal velocity, and other parameters. On the large scale the velocity U increases smoothly from 8 m a−1, 800 km inland, to 280 m a−1 inland of the fast outlet streams. This increase in velocity is associated with a corresponding increase in the large-scale smoothed (over about 30 ice thicknesses) basal shear stress τb from 0.4 to 1.5 bar. The mean shear strain-rate through the ice sheet U/Z = kτb4 , where Z is the ice thickness (range 4 500 to 1 700 m). At scales of one to several ice thicknesses large variations occur in surface slope and ice thickness without proportionally large velocity variations, because of the effect of the longitudinal stress. Detailed measurements made over a 30 km section indicated that the surface longitudinal strain-rate gradient varied from -1.7 to +1.3×l0−6 a−1 m−1 along with variations in surface slope of from -3.5 to +1.5%. A multilayer model, based on the solution of the biharmonic equation for the stream function, was used in a study of the ice flow associated with these surface undulations. Given the bedrock topography and large-scale flow parameters, the model closely predicted the measured surface profile when the variation of the surface accumulation rate over an undulation was also considered.

scholarly journals Deformation in the Vicinity of Ice Divides

1983 ◽  
Vol 29 (103) ◽  
pp. 357-373 ◽  
Author(s):  
Charles F. Raymond
Keyword(s):  
Finite Elements ◽  
Laminar Flow ◽  
Velocity Profile ◽  
Strain Rate ◽  
Shear Strain ◽  
Vertical Velocity ◽  
Flow Theory ◽  
Numerical Calculations ◽  
Shear Strain Rate ◽  
Horizontal Shear

AbstractNumerical calculations by finite elements show that the variation of horizontal velocity with depth in the vicinity of a symmetric, isothermal, non-slipping ice ridge deforming on a flat bed is approximately consistent with prediction from laminar flow theory except in a zone within about four ice thicknesses of the divide. Within this near-divide zone horizontal shear strain-rate is less concentrated near the bottom and downward velocity is less rapid in comparison to the flanks. The profiles over depth of horizontal and vertical velocity approach being linear and parabolic respectively. Calculations for various surface elevation profiles show these velocity profile shapes are insensitive to the ice-sheet geometry.

Sign in / Sign up

Export Citation Format

Share Document