Microstructural evolution of ice under simple shear deformation

To investigate microstructure in ice deformed under simple shear conditions experiments were performed with artificial polycrystalline ice and natural ice samples form Vatnajökull glacier in Iceland. A new deformation apparatus was tested and results from deformation were compared to literature to validate the method. Boundary conditions for deformation were varied. Experiments were performed at -5°C and -10°C and three strain rates were applied (2.5x10-7 1/s, 1.25x10-6 1/s, 2.5x10-6 1/s). It is shown that the natural samples, which contain only 2-3 grains, provide a close-up image on specific situation. This gives the opportunity to study them in detail. A special focus is set on the behaviour of grain boundaries during deformation. A preferred arrangement with at least one side of the boundary close to a prism face is seen. While in warm or slow deformations a tendency to favour boundaries with a combination of {1̅ 1̅ 22} and {101̅ 2} faces. The type of crystall face and their orientation towards deformation direction befor deformation has an major influence on the development during deformation. Brittle fractures were observed in the samples, which immediately filled with small new grains. This was only observed in samples deformed at -10°C but no dependency to strain rate was oberved