The ice single crystal possesses a strong viscoplastic anisotropy, it deforms mainly by dislocation glide in the basal plane. A constitutive model for the single crystal behaviour, based on existing models for metals, is proposed to reproduce the experimental results cited in the literature. In polycrystalline ice, this strong viscoplastic anisotropy leads to incompatibilities of deformation between the grains, which induce strain heterogeneities inside the grains. To study the mechanisms leading to the localization of the deformation, creep experiments were carried out in cold room on laboratory-made ice specimens, constituted of a multicrystal included in a macroscopically isotropic ice matrix. The deformation was followed by photographs of the specimens taken at regular time intervals, a more precise observation being done with an optical microscope after each test. Di fferent con gurations of the inclusion allowed to obtain an homogeneous strain fi eld in the inclusion, or on the contrary to provoke the localization of deformation in the form of kink bands, bending bands or polygonization. A constitutive law, considering the ice grain as a transversely isotropic continuum possessing a weak resistance for shear parallel to the basal planes, was used in a fi nite-element code to simulate the experiments. When the strain field is homogeneous (monocrystalline inclusion), the simulations reproduce with a good accuracy the experiments. In the case of a multicrystalline inclusion, the simulations allow to reproduce relatively well the global shape and the crystallographic orientation of the grains, and give informations on the locations where kink bands are likely to appear.
Contribution à l'étude du comportement viscoplastique d'un multicristal de glace : hétérogénéité de la déformation et localisation, expériences et modèles.