Dislocation motion in ice: A study by synchrotron X-ray topography

Ahmad, Shoaib; Whitworth, R. W.

doi:10.1080/01418618808209918

Cited by 96 publications

(48 citation statements)

References 18 publications

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“…At root are sluggish dislocation kinetics (e.g., see Ahmad and Whitworth 1988;Shearwood and Whitworth 1991). Owing to its crystal structure, ice Ih slips preferentially on the basal planes, and this is impeded by the unique requirement of protonic rearrangement (Glen 1968).…”

Section: Ductile-brittle Transitionmentioning

confidence: 99%

The fracture of water ice Ih: A short overview

Schulson¹

2006

Meteorit & Planetary Scien

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Abstract-This paper presents a short overview of the fracture of water ice Ih. Topics include the ductile-to-brittle transition, tensile and compressive strength, compressive failure under multiaxial loading, compressive failure modes, and brittle failure on the geophysical scale (Arctic sea ice cover, Europa's icy crust). Emphasis is placed on the underlying physical mechanisms. Where appropriate, comment is made on the formation of high-latitude impact craters on Mars.

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Section: Ductile-brittle Transitionmentioning

confidence: 99%

The fracture of water ice Ih: A short overview

Schulson¹

2006

Meteorit & Planetary Scien

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“…[10] Multiplication of dislocations during transient creep was explained by the climb of 60 o basal dislocations on the {1 100} prismatic planes [Ahmad and Whitworth, 1988].…”

Section: Viscoplastic Behavior Of Ice Crystalsmentioning

confidence: 99%

Elastoviscoplastic micromechanical modeling of the transient creep of ice

et al. 2008

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[1] A salient feature of the rheology of isotropic polycrystalline ices is the decrease of the strain rate by more than 2 orders of magnitude during transient creep tests to reach a secondary creep regime at a strain which is systematically of $1%. We use a recent (socalled ''affine'') version of the self-consistent mean-field theory to model the elastoviscoplastic behavior of ice. The model aims at bridging scales between the rheology of single grain and the one of polycrystals by evaluating the intergranular interactions. It takes into account the long-term memory effects, which manifests itself by the fact that local stress and strain rate in grains depend on the whole mechanical history of the polycrystal. It is shown that the strong hardening amplitude during the transient creep is entirely explained by the stress redistribution within the specimen, from an almost uniform stress distribution upon instantaneous loading (purely elastic response) to strong interphase and intraphase heterogeneities in the stationary regime (purely viscoplastic response). The experimental hardening kinetic is much too slow to be explained by the same process; it is attributed to the hardening of hard glide slip systems (prismatic slip) in the transient regime. Moreover, the model very well reproduces the permanent creep rate of several highly anisotropic specimens of the Greenland Ice Core Project ice core (pronounced crystallographic textures), when accounting for a single-grain rheology that well matches the experimental one. Our results are consistent with recent findings concerning dislocation dynamics in ice.

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“…Whitworth andco-workers (Ahmad et al, 1986, 1992;Ahmad and Whitworth, 1988;Shearwood and Whitworth, 1989, 1992) pioneered the use of SWBXT for ice, using it to observe the dynamic behavior of dislocations in single crystals. As with conventional XT, the Burgers' vector of the slip dislocations was found to be 1 3 ͗112 0͘.…”

Section: Synchrotron X-ray Topographymentioning

confidence: 98%

“…The high-intensity X-ray beam produced by a synchrotron (about 100 times more intense than a conventional X-ray source) reduces exposure times to a few seconds, thus, eliminating defect structure instability problems arising from long exposure times of non-synchrotron-based topography (Ahmad and Whitworth, 1988) and allowing the possibility of true in situ observations of dynamic phenomena. 2.…”

Section: Synchrotron X-ray Topographymentioning

confidence: 99%

Imaging dislocations in ice

Baker

2003

Microscopy Res & Technique

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Three techniques have been used to study dislocations in ice: etch pitting-replication, transmission electron microscopy, and X-ray topography (XT). It is shown that, because ice is a weak absorber of X-rays and can be produced with a low dislocation density, allowing relatively thick specimens to be studied, the most useful technique is XT. The observations that have been made with conventional XT are briefly outlined. However, the introduction of high-intensity synchrotron radiation, with its concomitant short exposure times, showed that images obtained through conventional XT observations were of dislocations that had undergone recovery. The important dynamic observations and measurements that have been made using synchrotron X-ray topography are presented. Dynamic synchrotron X-ray topography observations of ice single crystals undergoing deformation in situ have shown that slip mainly occurs by the movement of screw and 60 degrees (1/3) [1120] dislocations on the basal plane, although non-basal slip by edge dislocations can also occur. The operation of Frank-Read and other dislocation multiplication sources have been clearly demonstrated and dislocation velocities have been measured. In contrast, in polycrystals, dislocation generation occurred at grain boundaries where there are stress concentrations before lattice dislocation generation mechanisms operate. Faulted dislocation loops have been determined to be mainly interstitial in both polycrystals and single crystals.

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Dislocation motion in ice: A study by synchrotron X-ray topography

Cited by 96 publications

References 18 publications

The fracture of water ice Ih: A short overview

The fracture of water ice Ih: A short overview

Elastoviscoplastic micromechanical modeling of the transient creep of ice

Imaging dislocations in ice

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