Jacques Meyssonnier

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.

Constitutive Modelling and Flow Simulation of Anisotropic Polar Ice

The different approaches explored by the authors to model the visco-plastic anisotropic behaviour of polar ice associated with the formation and evolution of fabrics, are reviewed. In order to achieve ice rheological models which can significantly improve the simulations of the evolution of ice sheets under varying climatic conditions, these models aim at taking into account the physical mechanisms likely to be active under the conditions prevailing in an ice sheet. Since the destination of a constitutive model for polar ice is its implementation into a large scale ice-sheet model, which is to be run extensively to simulate various climatic scenarios, some compromises must be made to limit its complexity. A possible solution is to use a hierarchy of models of increasing complexity. In this respect the results from the different models are compared and discussed from the viewpoint of ice-sheet flow modelling.

Experimental studies of the viscoplasticty of ice and snow

Polar ice sheets are fundamental elements of the climate system. Their extent and elevation have a direct influence on the global atmospheric circulation (through the albedo and wind intensity and direction) while the fresh water input from ice shelves and icebergs influence the ocean circulation. Furthermore the paleoclimatic records found in the deep ice cores drilled in polar ice sheets are an important source of information on the Earth climate mechanisms. As regards valley glaciers, as found in alpine regions, because they are very sensitive to temperature fluctuations they are nowadays considered as key indicators of present climate change. A good estimate of ice sheets mass balance response to climate change is needed to understand past sea level changes, while the mass balance of alpine glaciers is directly connected to present sea level rise. In this context it is very important to model the slow flow of glaciers and ice sheets, and to do so as well as possible, to improve our knowledge on the mechanical properties of ice. On the other hand, a wide range of engineering problems involve ice and snow mechanics, many of which in the high velocity or/and strain rate regimes (as for instance ice-structure interaction or snow avalanches). Since these later topics are exposed in other contributions to this book (see e.g. E. Schulson and M. Schneebeli) we will restrict ourselves to the very slow deformation of ice and snow in what glaciologist call the “viscoplastic regime”.

Etude expérimentale du frottement glace-béton: Cas des interactions glace-structure

ABSTRACT To understand the role of the contact conditions in the friction of ice on structure, we have performed cyclic friction tests at—10° C between laboratory grown columnar ice and a micro-concrete. This paper defines the performed tests. The obtained results allow the study of the mechanical behaviour of the interface and of the wear of concrete. Effects of time and contact conditions on friction are analysed, which leads to the formulation of empirical friction laws and to the definition of the physical mechanisms involved at the interface. The role of these mechanisms is tested in a simple model of the ice-concrete contact.