Preprints
https://doi.org/10.5194/egusphere-2024-331
https://doi.org/10.5194/egusphere-2024-331
10 Apr 2024
 | 10 Apr 2024

Evolution of crystallographic preferred orientations of ice sheared to high strains by equal-channel angular pressing

Qinyu Wang, Sheng Fan, Daniel H. Richards, Rachel Worthington, David J. Prior, and Chao Qi

Abstract. Plastic deformation of polycrystalline ice 1 h induces crystallographic preferred orientations (CPOs), which give rise to anisotropy in the viscosity of ice, thereby exerting a strong influence on the flow of glaciers and ice sheets. The development of CPOs is governed by two pivotal mechanisms: recrystallization dominated by subgrain/lattice rotation and by strain-induced grain boundary migration (GBM). To examine the impact of strain on the transition of the dominant mechanism, synthetic ice (doped with ∼1 vol.% graphite) was deformed using equal-channel angular pressing technique, enabling multiple passes to accumulate substantial shear strains. Nominal shear strains up to 6.2, equivalent to a nominal von Mises strain of ε′ ≈ 3.6, were achieved in samples at a temperature of −5 °C. Cryo-electron backscatter diffraction analysis reveals a primary cluster of crystal c axes perpendicular to the shear plane in all samples, accompanied by a secondary cluster of c axes at an oblique angle to the primary cluster antithetic to the shear direction. With increasing strain, the primary c-axis cluster strengthens, while the secondary cluster weakens. The angle between the clusters remains within the range of 45° to 60°. The c-axis clusters are elongated perpendicular to the shear direction, with this elongation intensifying as strain increases. Subsequent annealing of the highest-strain sample reveals the same CPO patterns as observed prior to annealing, albeit slightly weaker. A synthesis of various experimental data suggest that the CPO pattern, including the orientation of the secondary cluster, results from a balance of two competing mechanisms: lattice rotation due to dislocation slip, which fortifies the primary cluster while rotating and weakening the secondary one, and grain growth by strain-induced GBM, which reinforces both clusters while rotating the secondary cluster in the opposite direction. As strain increases, GBM contributes progressively less. This investigation supports the previous hypothesis that a single cluster of c axes could be generated in high-strain experiments, while further refining our comprehension of CPO development in ice.

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Qinyu Wang, Sheng Fan, Daniel H. Richards, Rachel Worthington, David J. Prior, and Chao Qi

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-331', Anonymous Referee #1, 10 Jul 2024
    • AC1: 'Reply on RC1', Chao Qi, 30 Sep 2024
  • RC2: 'Comment on egusphere-2024-331', Christopher Gerbi, 01 Sep 2024
    • AC2: 'Reply on RC2', Chao Qi, 30 Sep 2024
Qinyu Wang, Sheng Fan, Daniel H. Richards, Rachel Worthington, David J. Prior, and Chao Qi
Qinyu Wang, Sheng Fan, Daniel H. Richards, Rachel Worthington, David J. Prior, and Chao Qi

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Latest update: 12 Nov 2024
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Short summary
To examine if the single cluster fabric in natural ice is formed due to high strains, we deformed synthetic ice to large strains using a unique technique. A shear strain of 6.2 was achieved in laboratory. We explored how the two mechanisms, which control microstructure and fabric evolution, evolve with strain, and established a fabric development model. These results will help understanding the fabrics in natural ice and further comprehending glacier and ice sheet flow dynamics.