Plastie deformation of ice monocrystal is essentially due to dislocation glide in basal planes. Glide on other slip systems or eventually climb of basal dislocations limits the strain rate of polycrystalline ice. In polar ice sheets, a preferred c-axis orientation develops with strain, and induces and strong viscoplastie anisotropy. A ViscoPlastic Self-consistent (VPSC) approach is used for predicting mechanical behavior of polycrystalline ice and texture development. Results are compared to those of the uniform stress model (lower bound) and uniform strain rate model (upper bound). In these models, ice crystals are assumed to deform by basal, prismatic, and pyramidal slip. The slip system resistance of a grain in-situ is determined from the mechanical behavior (deterrnined experimentally) of strongly anisotropic polycrystalline samples.According to the VPSC model, the behavior of a grain in-situ is closed to that of an isolated monocrystal. This model perfectly reproduces the experimental behavior of anisotropic polycrystals. When polycrystalline ice is deformed by hard glide, the strain rate direction is very sensitive to the direction of the applied stress. Such deformation conditions should appear near the ice divide of ice sheets. In the upper layer of ice sheets (grain growth zone), the VPSC model gives a good estimation of texture development. In the deeper ice, rotation recrystallization has a significant influence on texture development. Mechanical tests in cold rooms indicate a tendency to a quasi-newtonien behavior under very low stress conditions.
