Intragranular strain ﬁeld in columnar ice during transient creep regime and relation with the local microstucture
Laboratoire de Glaciologie et Géophysique de l’Environnement,
CNRS/Université Joseph Fourier
2 Laboratoire Procédés et Ingénierie en Mécanique et Matériaux, CNRS/Arts et Metiers ParisTech, Paris, France
3 Laboratoire Systèmes et Matériaux pour la Mécatronique, Polytech Savoie, France
Transient effects in the creep of polycrystalline ice could play a crucial role for several ice ﬂows (e.g. interaction between Antarctic ice shelves and ocean tides) and also have a major impact concerning deformation mechanisms of ice. During creep deformation of polycrystalline ice, strong stress and strain-rate intragranular heterogeneities are expected. These heterogeneities come from the very large viscoplastic anisotropy of ice crystals (with essentially a single easy plane for the dislocations to glide) which is responsible for the strong mechanical interaction between adjacent grains . In order to go one step further in the quantitative understanding of this process, and to characterize the development of strain heterogeneities at a microscopic (intragranular) scale, we have performed deformation tests on 2-D polycrystalline ice exhibiting columnar grains with controlled grain size. Specimens were submitted to creep test and transient effects, in which both elastic and viscoplastic responses come in play, are investigated. A Digital Image Correlation (DIC) technique, with spatial resolution far smaller than the mean grain size, has been set to get continuous record of the intragranular displacement ﬁeld during the test . Experimental parameters have been optimized to improve the precision of the DIC results. In parallel, specimen microstructures were analyzed with an automatic ice texture analyzer, before and after deformation, and post-mortem measurements of local misorientations at the intragranular scale were performed. For the ﬁrst time in ice, this work presents a direct link between grain orientation, strain localization, and lattice distortion at the intragranular scale.
© Owned by the authors, published by EDP Sciences, 2010