Localization of deformation in polycrystalline ice: experiments and numerical simulations with a simple grain model

Creep tests were carried out on structure-controlled laboratory-made ice specimens to assess a simple constitutive model which accounts for the outstanding viscoplastic anisotropy of ice. A homogeneous deformation was observed when testing a circular monocrystalline inclusion embedded in a fine-grained isotropic ice matrix, whereas severe localization of the deformation, essentially in the form of kink bands, was observed in a multicrystalline inclusion made of a large central grain surrounded by a crown of medium-size grains. Finite-element simulations were performed by assuming that the grain behaves as a transversely isotropic medium. A very good agreement was obtained for the monocrystalline inclusion when using the grain model parameters derived from data on isolated ice single crystals. However, the simulation fails to reproduce accurately the heterogeneous deformation of the multicrystal, although it provides a good prediction of the locations where localization features are susceptible to appear.