DYNAMIC RECRYSTALLIZATION OF ICE IN POLAR ICE SHEETS

The deformation and recrystallization mechanisms which control the vis coplasticity of ice from polar ice sheets have been investigated. The high plastic anisotropy of ice crystals is responsible for the develop ment of a non uniform internal stress field within the polycrystal. St rain-shadows produced by sub-grain are observed in polarized light whe n the rotation recrystallization regime is dominant. Migration recryst allization occurs for a temperature higher than -10 degrees C. and is characterized by a unique relationship between recrystallized grain si ze and stress. The role of dynamic recrystallization in the developmen t of lattice preferred orientations is discussed. Lattice rotation by intracrystalline slip is the dominant mechanism when grain growth or r otation recrystallization occurs.