scholarly journals The Path-Independent M Integral Implies the Creep Closure of Englacial and Subglacial Channels

2016 ◽  
Vol 84 (1) ◽  
Author(s):  
Colin R. Meyer ◽  
John W. Hutchinson ◽  
James R. Rice
Keyword(s):  
Antiplane Shear ◽  
Far Field ◽  
Overburden Pressure ◽  
Hydrologic Systems ◽  
Path Independence ◽  
Essential Components ◽  
Drainage Channels ◽  
Stress States ◽  
Independent Integral ◽  
M Integral

Drainage channels are essential components of englacial and subglacial hydrologic systems. Here, we use the M integral, a path-independent integral of the equations of continuum mechanics for a class of media, to unify descriptions of creep closure under a variety of stress states surrounding drainage channels. The advantage of this approach is that the M integral around the hydrologic channels is identical to same integral evaluated in the far field. In this way, the creep closure on the channel wall can be determined as a function of the far-field loading, e.g., involving antiplane shear as well as overburden pressure. We start by analyzing the axisymmetric case and show that the Nye solution for the creep closure of the channels is implied by the path independence of the M integral. We then examine the effects of superimposing antiplane shear. We show that the creep closure of the channels acts as a perturbation in the far field, which we explore analytically and numerically. In this way, the creep closure of channels can be succinctly written in terms of the path-independent M integral, and understanding the variation with applied shear is useful for glacial hydrology models.

Effect of block rotation on the pitch of slickenlines

2011 ◽  
Vol 3 (1) ◽  
Author(s):  
Shunshan Xu ◽  
Ángel Nieto-Samaniego ◽  
Susana Alaniz-Álvarez ◽  
Luis Velasquillo-Martínez
Keyword(s):  
Stress Tensor ◽  
Normal Fault ◽  
Thrust Fault ◽  
Strike Slip ◽  
Far Field ◽  
Block Rotation ◽  
Calculated Stress ◽  
Stress States ◽  
Far Field Stress ◽  
Rotation Stress

AbstractRotation of faults or pre-existing weakness planes produce two effects on the slickenlines of fault planes. First, the rotation leads to changes in the pitch of slickenlines. As a result, the aspect of the pre-existing fault may change. For example, after rotation, a normal fault may show features of an oblique fault, a strike-slip fault, or a thrust fault. Second, due to rotation, stress states on the fault planes are different from those before the rotation. As a consequence some previous planes may be reactivated. For an isolated plane, the reactivation due to rotation can produce new sets of slickenlines. With block rotation, superimposed slickenlines can be generated in the same tectonic phase. Thus, it is not appropriate to use fault-slip data from slickenlines to analyze the stress tensor in a region where there is evidence of block rotation. As an example, we present the data of slickenlines from core samples in the Tunich area of the Gulf of Mexico. The results wrongly indicate that the calculated stress tensor deviates from the far-field stress tensor.

scholarly journals Novel wireless sensors for in situ measurement of sub-ice hydrologic systems

2014 ◽  
Vol 55 (65) ◽  
pp. 41-50 ◽  
Author(s):  
E.A. Bagshaw ◽  
B. Lishman ◽  
J.L. Wadham ◽  
J.A. Bowden ◽  
S.G. Burrow ◽  
...  
Keyword(s):  
Wireless Sensors ◽  
Low Cost ◽  
Water Pressure ◽  
Greenland Ice Sheet ◽  
Field Testing ◽  
Wireless Data ◽  
Sensor Platforms ◽  
Hydrologic Systems ◽  
Drainage Channels

AbstractWireless sensors have the potential to provide significant insight into in situ physical and biogeochemical processes in sub-ice hydrologic systems. However, the nature of the glacial environment means that sensor deployment and data return is challenging. We describe two bespoke sensor platforms, electronic tracers or ‘ETracers’, and ‘cryoegg’, for untethered, wireless data collection from glacial hydrologic systems, including subglacial channels. Both employ radio frequencies for data transmission, are designed to endure harsh environmental conditions and can withstand low temperatures, high pressure, turbulence and abrasion. We discuss the design, optimization and field testing of the ETracers and cryoegg, culminating in test deployments beneath the Greenland ice sheet. The small, low-cost ETracers were able to travel through subglacial drainage channels, from where they returned water pressure measurements through 100 m of ice, and could measure water depth in crevasses. The larger cryoegg was able to return multi-parameter data from moulins through 500 m of wet ice to receivers up to 2 km away, and from 12 m depth in a proglacial lake to a receiver on the shore. The tests demonstrate that the cryoegg and ETracers are low-power, versatile, robust wireless sensor platforms suitable for glacial environments, which may be used with portable, low-cost receiving equipment.

Diffraction of SH-Waves by an Edge Crack

1979 ◽  
Vol 46 (1) ◽  
pp. 101-106 ◽  
Author(s):  
S. K. Datta
Keyword(s):  
Stress Intensity Factor ◽  
Nondestructive Evaluation ◽  
Edge Crack ◽  
Dynamic Stress ◽  
Near Field ◽  
Dynamic Stress Intensity Factor ◽  
Antiplane Shear ◽  
Far Field ◽  
Sh Wave ◽  
Sh Waves

Diffraction of an antiplane shear (SH-) wave by an edge crack in a semi-infinite elastic medium is studied here. Asymptotic expansions for the scattered field both near and far from the crack are obtained for the case when the wavelength is large compared to the length of the crack. Near-field expansion is used to compute the dynamic stress-intensity factor at the tip of the crack. Also, the far-field expansion gives the scattered displacement amplitude, which is useful in ultrasonic nondestructive evaluation.

The Nature of Crack Tip Fields in Atomic Scale Models of Aluminum

1990 ◽  
Vol 193 ◽  
Author(s):  
R. G. Hoagland ◽  
M. S. Daw ◽  
S. M. Foiles ◽  
M. I. Baskes
Keyword(s):  
Surface Energy ◽  
Crack Tip ◽  
Atomic Scale ◽  
Dislocation Emission ◽  
Linear Elastic ◽  
Path Independence ◽  
Scale Models ◽  
Sharp Crack ◽  
Good Agreement ◽  
M Integral

ABSTRACTThe stresses, displacement gradients, and Eshelby's F and M integrals are obtained for two crack orientations in an EAM atomic model of aluminum. For a sharp crack, the stresses are shown to agree quite well with the linear elastic prediction, and F is essentially path independent and also in good agreement with the linear elastic prediction. When dislocation emission and blunting ensues, the path independence of F disappears. In addition, for circular contours with origin at the crack tip, the M-integral is linear in contour radius with slope equal to twice the surface energy and zero intercept for a sharp crack, but acquires a nonzero intercept as blunting occurs. The shift in intercept is related to the movement of singularities away from the origin.

Poroelastic Solution for an Inclined Borehole

1997 ◽  
Vol 64 (1) ◽  
pp. 32-38 ◽  
Author(s):  
L. Cui ◽  
A. H-D. Cheng ◽  
Y. Abousleiman
Keyword(s):  
Analytical Solution ◽  
Plane Strain ◽  
Antiplane Shear ◽  
Far Field ◽  
Poroelastic Medium ◽  
Principal Stresses ◽  
Decomposition Scheme ◽  
Shear Problem ◽  
Inclined Borehole

The analytical solution for an infinitely long borehole in an isotropic, poroelastic medium, inclined to the far-field principal stresses, is presented. The solution utilizes a loading decomposition scheme which leads to three fundamental problems: a poroelastic plane-strain, an elastic uni-axial, and an elastic antiplane shear problem.

Comparison of Substructures Between Uniaxial and Biaxial Deformation in 1100-0 Aluminum

1981 ◽  
Vol 39 ◽  
pp. 52-53
Author(s):  
D. L. Rohr ◽  
S. S. Hecker
Keyword(s):  
Plastic Strain ◽  
Cell Walls ◽  
Room Temperature ◽  
Mechanical Response ◽  
Biaxial Tension ◽  
Initial Deformation ◽  
Uniaxial Deformation ◽  
Biaxial Deformation ◽  
Stress States ◽  
Comprehensive Study

As part of a comprehensive study of microstructural and mechanical response of metals to uniaxial and biaxial deformations, the development of substructure in 1100 A1 has been studied over a range of plastic strain for two stress states.Specimens of 1100 aluminum annealed at 350 C were tested in uniaxial (UT) and balanced biaxial tension (BBT) at room temperature to different strain levels. The biaxial specimens were produced by the in-plane punch stretching technique. Areas of known strain levels were prepared for TEM by lapping followed by jet electropolishing. All specimens were examined in a JEOL 200B run at 150 and 200 kV within 24 to 36 hours after testing.The development of the substructure with deformation is shown in Fig. 1 for both stress states. Initial deformation produces dislocation tangles, which form cell walls by 10% uniaxial deformation, and start to recover to form subgrains by 25%. The results of several hundred measurements of cell/subgrain sizes by a linear intercept technique are presented in Table I.

Possible applications of fraunhofer holography in high resolution electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 222-223 ◽  
Author(s):  
N. Bonnet ◽  
M. Troyon ◽  
P. Gallion
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Transfer Function ◽  
Radiation Damage ◽  
High Resolution Electron Microscopy ◽  
Far Field ◽  
Field Region ◽  
Crystalline Materials ◽  
Resolution Electron ◽  
The Ideal

Two main problems in high resolution electron microscopy are first, the existence of gaps in the transfer function, and then the difficulty to find complex amplitude of the diffracted wawe from registered intensity. The solution of this second problem is in most cases only intended by the realization of several micrographs in different conditions (defocusing distance, illuminating angle, complementary objective apertures…) which can lead to severe problems of contamination or radiation damage for certain specimens.Fraunhofer holography can in principle solve both problems stated above (1,2). The microscope objective is strongly defocused (far-field region) so that the two diffracted beams do not interfere. The ideal transfer function after reconstruction is then unity and the twin image do not overlap on the reconstructed one.We show some applications of the method and results of preliminary tests.Possible application to the study of cavitiesSmall voids (or gas-filled bubbles) created by irradiation in crystalline materials can be observed near the Scherzer focus, but it is then difficult to extract other informations than the approximated size.

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