Mechanics and microstructure of deformed natural anisotropic ice

Lisa Craw, Chao Qi, David J. Prior, David L. Goldsby, Daeyeong Kim

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

We deformed coarse-grained (∼10 mm) natural ice in axial compression at −30 °C, to an axial strain of 0.2, at three different angles to the existing strong crystallographic preferred orientation (CPO). We used three strain rates for each sample orientation. Cryo-electron backscatter diffraction (EBSD) maps show that after deformation there is a mixture of large (∼1–2 mm) relict grains, and finer (100–200 μm) recrystallised grains. The fine grains form a connected network in all samples. The large grains define a very strong CPO with equivalent but weaker CPOs in the recrystallised grains. The final CPO changed completely from its original orientation. Lattice distortion and subgrains equivalent in size to recrystallised grains suggest a subgrain rotation recrystallisation process has generated the recrystallised fraction. We suggest that strain rates were higher in the connected network of recrystallised grains because of a significant component of grain boundary sliding (GBS) that enables large grains to rotate by a combination of glide on the basal plane and rigid rotation, to define a very strong CPO. GBS weakens the CPO in the finer grained regions. The patterns of mechanical behaviour and the resultant microstructures do not bear an obvious relationship to original CPO.

Original languageEnglish (US)
Pages (from-to)152-166
Number of pages15
JournalJournal of Structural Geology
Volume115
DOIs
StatePublished - Oct 2018

Bibliographical note

Funding Information:
We are grateful to Marianne Negrini and Sheng Fan for help with the EBSD analysis, Travis Hager for assistance in the laboratory, Pat Langhorne for the use of her cold rooms, and Yeongcheol Han for ice sampling. This research was made possible by funding provided by the Todd Foundation , the New Zealand Antarctic Research Institute , the Trans-Antarctic Association , KOPRI project PM18030 ( 20140409 ), Marsden Fund UOO052 of the Royal Society of New Zealand , and a University of Otago Research Grant 2018.

Keywords

  • Crystallographic preferred orientations
  • Glaciology
  • Grain boundary sliding
  • Ice deformation
  • Ice microstructure

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