HR: 09:16h
AN: MR11A-06    [Abstracts]
TI: New Developments in the Understanding of the Deformation Behaviour of ice
AU: * Duval, P
EM: duval@lgge.obs.ujf-grenoble.fr
AF: Duval, LGGE/CNRS BP 96, St. Martin d'Heres, 38402, France
AB: Single crystals undergo plastic deformation as soon as there is a component of shear stress on the basal plane. Basal slip is observed for shear stresses in the basal plane lower than 0.02 MPa and takes place by the motion of basal dislocations. Non-basal slip associated with the cross slip of basal screw dislocations is invoked for the multiplication of dislocations. But, its contribution to the deformation of the ice crystal is very small. Due to the low lattice friction, dislocations glide cooperatively and long-range internal stresses develop with deformation. The plastic deformation takes place through isolated bursts or dislocation avalanches as soon as diffusion processes are not significant. Then, the plastic deformation of the ice crystal is characterized by large spatio- temporal fluctuations with scale-invariant patterns. In polar ice sheets, the viscous deformation is essentially produced by basal slip. The other deformation modes required for compatibility reasons can be non-basal slip or the climb of dislocations. These deformation modes give a stress exponent of about 3 provided that dynamic recrystallization is not very active. At low deviatoric stresses, typically lower than 0.1 MPa, the stress exponent can be slightly lower than 2. Basal slip is still the dominant deformation mode. But, it can be accommodated by grain boundary sliding and/or grain boundary migration. A grain size effect is expected for this deformation regime. At the both scales of the ice crystal and the polycrystal, the deformation is highly heterogeneous. This behaviour is associated with the anisotropy of the ice crystal and the mismatch of slip at grain boundaries for the polycrystal. Strain rates fluctuations within grains increase with the development of textures whereas stress fluctuations decrease. The viscoplastic deformation induces the development of lattice preferred orientations (textures) giving a non-random orientation of the c-axes in the largest part of ice sheets and making ice strongly anisotropic. Recrystallization textures associated with dynamic recrystallization are generally found near the bottom where temperature is the highest.
DE: 0738 Ice (1863)
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 3902 Creep and deformation
DE: 5120 Plasticity, diffusion, and creep
DE: 5422 Ices
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting