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Basal slip of dislocations, the easiest deformation mechanism of ice crystals, does not allow a response to any strain state. The first steps of another mechanism, with a moving subgrain boundary precursor region, which permits accommodating the effect of an applied load, is investigated on an ice single crystal, mainly using synchrotron radiation Bragg diffraction imaging. During this process, the evolution of the local integrated intensity shows that there is both a general multiplication of dislocations within the crystal and a movement of basal dislocations towards the surface. The `subgrain boundary precursor' region evolves towards a classical grain boundary when further deformed. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]