scholarly journals Structure and Flow in the Margin of the Barnes Ice Cap, Baffin Island, N.W.T., Canada

1973 ◽  
Vol 12 (66) ◽  
pp. 423-438 ◽  
Author(s):  
Roger Leb. Hooke
Keyword(s):  
Flow Field ◽  
Strain Rate ◽  
Effective Strain ◽  
The Other ◽  
Baffin Island ◽  
Glacier Surface ◽  
Effective Strain Rate ◽  
Ice Cap ◽  
Single Maximum ◽  
Flow Law

The structure and flow field in the margin of the Barnes Ice Cap was determined through observations on the ice-cap surface, in four bore holes, and in a 125 m ice tunnel. A band of fine bubbly white ice with a single maximum fabric appears at the glacier surface about 160 m from the margin. This band is overlain by coarse blue ice with a four-maximum fabric, and underlain by alternating bands of fine ice with a single-maximum fabric and moderately coarse ice with a two or three-maximum fabric. The effective strain rate was determined from the bore-hole and tunnel deformation data, and possible variations in the other three parameters in Glen’s flow law, , were studied. It appears that τ xy is independent of depth near the surface, and that relative to the coarse blue ice, A is 40 to 50% lower in the white ice and possibly 10% lower in the fine blue ice. Dips of foliation planes decrease rapidly with increasing depth and distance from the margin. This foliation is assumed to have developed near and parallel to the bed some distance from the margin. An analysis based on this assumption predicts the observed change in dip, but suggests that it did not develop under the present flow field. The ice cap was probably thicker a few tens of years ago, and the observed foliation pattern may be a relict from that time.

scholarly journals Structure and Flow in the Margin of the Barnes Ice Cap, Baffin Island, N.W.T., Canada

1973 ◽  
Vol 12 (66) ◽  
pp. 423-438 ◽  
Author(s):  
Roger Leb. Hooke
Keyword(s):  
Flow Field ◽  
Strain Rate ◽  
Effective Strain ◽  
The Other ◽  
Baffin Island ◽  
Glacier Surface ◽  
Effective Strain Rate ◽  
Ice Cap ◽  
Single Maximum ◽  
Flow Law

The structure and flow field in the margin of the Barnes Ice Cap was determined through observations on the ice-cap surface, in four bore holes, and in a 125 m ice tunnel. A band of fine bubbly white ice with a single maximum fabric appears at the glacier surface about 160 m from the margin. This band is overlain by coarse blue ice with a four-maximum fabric, and underlain by alternating bands of fine ice with a single-maximum fabric and moderately coarse ice with a two or three-maximum fabric.The effective strain rate was determined from the bore-hole and tunnel deformation data, and possible variations in the other three parameters in Glen’s flow law, , were studied. It appears that τxy is independent of depth near the surface, and that relative to the coarse blue ice, A is 40 to 50% lower in the white ice and possibly 10% lower in the fine blue ice.Dips of foliation planes decrease rapidly with increasing depth and distance from the margin. This foliation is assumed to have developed near and parallel to the bed some distance from the margin. An analysis based on this assumption predicts the observed change in dip, but suggests that it did not develop under the present flow field. The ice cap was probably thicker a few tens of years ago, and the observed foliation pattern may be a relict from that time.

scholarly journals An anisotropic flow law for ice-sheet ice and its implications

1996 ◽  
Vol 23 ◽  
pp. 202-208 ◽  
Author(s):  
Nobuhiko Azuma ◽  
Kumiko Goto-Azuma
Keyword(s):  
Strain Rate ◽  
Stress Condition ◽  
Ice Sheet ◽  
Geometrical Factor ◽  
Strain Rate Tensor ◽  
Horizontal Shear ◽  
Anisotropic Flow ◽  
Single Maximum ◽  
Polycrystalline Ice ◽  
Flow Law

A new flow law for anisotropic polycrystalline ice is presented. The strain-rate tensor is related by a geometrical factor tensor (G) to the stress tensor. The G factor tensor can be obtained front the c-axis fabric data and stress condition. This new flow law describes well the direction-dependent mechanical properties of anisotropic ice which cannot be demonstrated by Glen’s flow law. For example, the new flow law can explain the fact that a strong single-maximum fabric ice, such as Dye 3 Wisconsin ice, can deform several times faster than isotropic ice under horizontal shear but can hardly deform under vertical or horizontal normal stress. We also show that at a deeper part of an ice sheet, where a single-maximum fabric develops, a positive vertical strain rate can be produced with only a horizontal shear stress.

scholarly journals Recording Wire Strainmeters on the Barnes Ice Cap, Baffin Island, Canada

1978 ◽  
Vol 20 (83) ◽  
pp. 409-423 ◽  
Author(s):  
K. Evans ◽  
D.J. Goodman ◽  
G. Holdsworth
Keyword(s):  
Strain Rate ◽  
Periodic Variation ◽  
Strain Rates ◽  
Baffin Island ◽  
Rate Data ◽  
Rapid Acquisition ◽  
Ice Cap ◽  
Good Agreement

AbstractThe report describes an experiment to evaluate the use of geophysical (Cambridge-type) wire strainmeters for the rapid acquisition of strain-rate data and to compare strains on a large ice mass over gauge distances of 5 m, 50 m, and 1 km.Three continuously recording wire strainmeters were installed at the centre of two separate arrays of strain poles 10.6 km and 19.5 km from the ice divide on the Barnes Ice Cap. Data was collected between 24 April and 15 May 1976. The 1 km strain arrays had previously been measured in 1974 and 1975. The results show good agreement between the strainmeter data and the larger strain arrays at the 10.6 km site but differ at the 19.5 km site. When the daily means are calculated for the strainmeters at the 19.5 km site, the strain-rates show a possible periodic variation with an apparent period ofabout 11 d. Since there appears to be no direct correlation between the strainmeter signal and either temperature or pressure, the result is assumed to represent real varying strain within the ice.

Creep Analysis of Orthotropic Rotating Cylinder

1980 ◽  
Vol 102 (4) ◽  
pp. 371-377 ◽  
Author(s):  
N. S. Bhatnagar ◽  
V. K. Arya ◽  
K. K. Debnath
Keyword(s):  
Strain Rate ◽  
Effective Stress ◽  
Anisotropic Material ◽  
Isotropic Material ◽  
Effective Strain ◽  
Angular Speed ◽  
Stress And Strain ◽  
Tangential Strain ◽  
Effective Strain Rate ◽  
Stress And Strain Rate

The stress and strain-rate distributions in the wall of a hollow thick-walled circular cylinder, rotating about its own axis with a constant angular speed, have been obtained using Norton’s law for the steady-state creep. The cylinder is assumed to be made of a homogeneous and orthotropic material. The numerical computations, for a number of steels and steel alloys commonly used to manufacture the cylinder, have been carried out for three cases of anisotropy. The effect of anistropy and of exponent n in creep law has been studied. It is observed that the stress and strain-rate distributions are significantly affected by the anisotropy of material and the value of exponent n. It is also noticed that the values of the effective stress for an anisotropic material for which the ratios of axial to tangential strain rate and of radial to tangential strain rate are equal to 1.2, are lower than the corresponding values for an isotropic material for which these ratios are 1.0. And, because of a power law between effective strain rate and effective stress, much lower values of the effective strain rate for the foregoing anisotropic material than those for the isotropic material will be obtained. Thus the use of the aforementioned anisotropic material may be beneficial for the manufacture of the cylinders because (i) it will result in a longer life for the cylinders (because of the lowest strain rate), or (ii) it will allow the cylinder to sustain larger forces without a risk of failure under creep.

Thermal Stresses near the Surface of a Glacier

1978 ◽  
Vol 20 (83) ◽  
pp. 257-283 ◽  
Author(s):  
T. J. O. Sanderson
Keyword(s):  
Strain Rate ◽  
Thermal Stresses ◽  
Overburden Pressure ◽  
Ice Cap ◽  
Short Period ◽  
Thermal Origin ◽  
Fourier Theory ◽  
Flow Law ◽  
Set Up ◽  
Strain Rate Field

AbstractStresses occur in the uppermost 10 m of a glacier as a result of temperature fluctuations at the surface. A model is set up of a typical year's surface temperature variation, and the progress of temperature waves through the glacier is calculated using Fourier theory of heat conduction. Short-period fluctuations are rapidly attenuated, and at 10 m depth the annual cycle is reduced to 5% of its surface amplitude. As the temperature of the ice varies it undergoes small volume changes; stresses are calculated on the assumption that any tendency of the ice to expand or contract laterally results in the creation of just enough stress to cause the ice to remain unstrained. It is found that in the top 2 or 3 m stresses of thermal origin are generally in excess of those due to gross deformation or overburden pressure. For the case of high-density ice Glen's flow law is used, and conditions are found to be favourable for the formation of surface rumples of wavelength about 10 m. For the case of firm or snow a Newtonian flow law is assumed, and it is found that under cold conditions fracture under tension can occur. Cracks of thermal origin may be responsible for the initial formation of crevasses, and they also provide an explanation for background noise encountered when seismic shooting at low temperatures. Calculations are made of the strain-rate field surrounding a crack and it is found that thermal effects can lead to appreciable Strain-rate anomalies for strain-rate measurements near cracks. The magnitude of the effect is easily sufficient to account for anomalous fluctuating strain-rates found by workers using wire strainmeters on the Barnes Ice Cap.

scholarly journals Radio Depth Sounding on Barnes Ice Cap

1975 ◽  
Vol 15 (73) ◽  
pp. 458-459 ◽  
Author(s):  
R. A. O’Neil ◽  
S. J. Jones
Keyword(s):  
The Other ◽  
Positioning System ◽  
Baffin Island ◽  
Velocity Change ◽  
Ice Cap ◽  
Depth Sounding ◽  
Attenuation Values

In May 1974 two radio depth sounders were used on the Barnes Ice Cap, Baffin Island. One was a S.P.R.I. 35 MHz sounder and the other was a unit operating at 620 MHz. Bottom reflections were observed with both systems at similar depths, indicating no significant velocity change between the two frequencies. Used with a Motorola range positioning system, the 620 MHz unit proved an excellent depth-survey vehicle. Results along the so-called surge profile (Holdsworth, 1973) are presented. Depth and attenuation values are compared with previous data.

Flow Characteristics Through Conical Converging Dies

1966 ◽  
Vol 88 (4) ◽  
pp. 410-419 ◽  
Author(s):  
B. Avitzur
Keyword(s):  
Velocity Field ◽  
Strain Rate ◽  
Effective Strain ◽  
Flow Characteristics ◽  
Published Data ◽  
Grid Pattern ◽  
Effective Strain Rate ◽  
Strain And Strain Rate ◽  
Distorted Grid ◽  
Flow Through

A velocity field is considered to describe flow through conical dies. The expected distorted grid pattern is studied. Strain and strain rate fields are analyzed. Effective strain and effective strain rate distributions and their averages are defined. Application to processes like drawing extrusion and hydrostatic extrusion is discussed. Analysis is compared with experimental published data.

scholarly journals Size- and speed-dependent mechanical behavior in living mammalian cytoplasm

2017 ◽  
Vol 114 (36) ◽  
pp. 9529-9534 ◽  
Author(s):  
Jiliang Hu ◽  
Somaye Jafari ◽  
Yulong Han ◽  
Alan J. Grodzinsky ◽  
Shengqiang Cai ◽  
...  
Keyword(s):  
Strain Rate ◽  
Optical Tweezers ◽  
Effective Strain ◽  
State Diagram ◽  
Elastic Solid ◽  
Incompressible Material ◽  
Cell Physiology ◽  
Mechanical Resistance ◽  
Scaling Analysis ◽  
Effective Strain Rate

Active transport in the cytoplasm plays critical roles in living cell physiology. However, the mechanical resistance that intracellular compartments experience, which is governed by the cytoplasmic material property, remains elusive, especially its dependence on size and speed. Here we use optical tweezers to drag a bead in the cytoplasm and directly probe the mechanical resistance with varying size a and speed V. We introduce a method, combining the direct measurement and a simple scaling analysis, to reveal different origins of the size- and speed-dependent resistance in living mammalian cytoplasm. We show that the cytoplasm exhibits size-independent viscoelasticity as long as the effective strain rate V/a is maintained in a relatively low range (0.1 s−1 < V/a < 2 s−1) and exhibits size-dependent poroelasticity at a high effective strain rate regime (5 s−1 < V/a < 80 s−1). Moreover, the cytoplasmic modulus is found to be positively correlated with only V/a in the viscoelastic regime but also increases with the bead size at a constant V/a in the poroelastic regime. Based on our measurements, we obtain a full-scale state diagram of the living mammalian cytoplasm, which shows that the cytoplasm changes from a viscous fluid to an elastic solid, as well as from compressible material to incompressible material, with increases in the values of two dimensionless parameters, respectively. This state diagram is useful to understand the underlying mechanical nature of the cytoplasm in a variety of cellular processes over a broad range of speed and size scales.

scholarly journals Plane ice-sheet flow with evolving and recrystallizing fabric

2003 ◽  
Vol 37 ◽  
pp. 247-251 ◽  
Author(s):  
Ryszard Staroszczyk
Keyword(s):  
Strain Rate ◽  
Large Scale ◽  
Effective Strain ◽  
Ice Sheet ◽  
Local Strain ◽  
Anisotropic Fluid ◽  
Recrystallization Process ◽  
Polar Ice ◽  
Ice Cap ◽  
Polar Ice Sheets

AbstractA plane, gravity-driven, steady flow of a polar ice sheet over a horizontal bedrock, with no-slip basal conditions, is considered. The ice is modelled as a linearly viscous, incompressible and anisotropic fluid, with evolving orthotropic fabric depending on local strain rates and deformations. For prescribed free-surface elevation and non-uniform temperature field, the ice velocities required to maintain the assumed geometry are calculated by using the finite-element method. The focus is on the mechanism of dynamic (migration) recrystallization occurring near the base ofan ice sheet and leading to significant weakening, and ultimately to the complete loss, of the anisotropic fabric developed in the upper part of the ice cap. The weakening of the fabric with increasing strain rate and temperature is modelled by means of a scaling function depending continuously on a single effective strain-rate invariant. The results of numerical calculations demonstrate the effect of the recrystallization process on the overall flow rate of the ice sheet, and normalized velocity and strain-rate depth profiles are compared for flows with and without recrystallization involved to illustrate the effect of this mechanism on the large-scale behaviour of polar ice sheets.

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