Search

Both optical microscopy with polarized light and polychromatic beam synchrotron X-ray diffraction imaging (white-beam topography) are used to study in situ the way an ice single-crystal deforms., 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.

The study of the distribution of the crystallographic orientations (the fabric) along ice cores supplies information on the past and current ice flows of ice-sheets. Beside the usually observed formation of a vertical single maximum fabric, the EPICA Dome Concordia ice core (EDC) shows an abrupt and unexpected strenghtening of its fabric during termination II around 1750 m depth. Such strengthenings were already observed for sites located on an ice-sheet. This suggests that horizontal shear could occur along the EDC core. Moreover, the change in the fabric leads to a modification of the viscosity between neighbouring ice layers. Through the use of an anisotropic ice flow model, we quantify the change in viscosity and investigate its implication on ice flow and dating.

Under high hydrostatic pressure combined with shear, the structure of polycrystalline ice breaks down into fine-grained material by a process of recrystallization. Accompanying this process is a substantial softening of the material. Measurements of activation energy at low strains prior to the breakdown of structure, at temperatures of -10 °C, show an increase of activation energy from about 80 kJ mol-1 to about 120 kJ mol -1 as the pressure increases, with values at about 70 MPa similar to those found by other researchers for temperatures between -10 and 0 °C. These results suggest that grain boundary effects might result in the increased strain rates. The various energies that might drive the subsequent recrystallization process have been investigated. The results suggest strongly that elastic strain energy is the driving force in the process., 18th International Conference on Port and Ocean Engineering under Arctic Conditions, POAC 2005, June 26-30, 2005, Potsdam, NY; USA

The present study deals with snowpack motions and its interaction with a snow flexible supportingstructure. The final aim of this research is to evaluate forces induced into a snow net system by its interactionwith a snowpack. This calculation will allow obtaining a better engineering design of these structures.A 2D continuous approach was developed where the snowpack is described by a FEM code in which avisco-plastic constitutive model was implemented. A Coulomb-type friction law is used in the snowpack -cable interface. In parallel, 2D discrete simulations are also performed in which the snowpack is representedby a set of rigid rectangular elements gliding between each other. In the both model, the same constitutive relationis used, and the cable is described by a set of nodes linked with their closest neighbors by linear elasticforces. As first elements of validation, some comparisons were done with experimental measurements.