Viscoplastic modeling of texture development in polycrystalline ice with a self-consistent approach: Comparison with bound estimates

Ice crystals deform easily by dislocation glide on basal planes, which provides only two independent easy slip systems. The necessary slip on other systems limits the strain rate of polycrystalline ice, The preferred c axis orientation of ice from polar ice sheets develops as a result of intracrystalline slip, An anisotropic viscoplastic self-consistent (VPSC) approach is used for predicting texture development and mechanical behavior of polycrystalline ice. Results are compared with lower and upper bound estimations. It is assumed that ice crystals deform by basal, prismatic, and pyramidal slip. The resistance of each slip system is determined from experimental data on monocrystals and isotropic polycrystals. The VPSC model can predict the behavior of isotropic polycrystalline ice on both the macroscopic and microscopic scale. This is not the case for the lower and upper bounds. Fabrics simulated in uniaxial extension and compression are qualitatively similar for all models. However, large differences in the rate of fabric development are found. This is explained by the different interaction stiffness between grain and matrix. Fabric concentration obtained with the VPSC model for uniaxial deformation is in close agreement with those observed in polar ices, In simple shear, the single maximum fabric found in situ cannot be reproduced without an extensive (and probably unrealistic) activity of nonbasal systems, The preferential growth of grains well oriented for basal glide associated with rotation recrystallization could be at the origin of the discrepancy between model results and natural simple shear fabrics. Distorted grain shape is found to slightly slow down fabric development.