On Friction and Surface Cracking During Sliding of Ice on Ice

As a complement to earlier measurements on the friction of both granular fresh-water ice and S2 columnar salt-water ice, new experiments were performed on the friction of S2 columnar fresh-water ice sliding against itself at low velocities (5 × 10−7 to 5 × 10−1 m s−1) and at −10°C, using the same double-shear device as was used earlier. The results showed that under a given set of experimental conditions the kinetic coefficient of friction of S2 fresh-water ice compares favorably with that of the other two variants.The experiments also revealed friction-induced surface cracks and recrystallized grains.These deformation features are explained, respectively, in terms of fracture mechanics and an earlier model of dynamic recrystallization in ice

Investigation of a cold-based ice apron on a high-mountain permafrost rock wall using ice texture analysis and micro-14C dating : a case study of the Triangle du Tacul ice apron (Mont Blanc massif, France)

This study is part of the ANR 14-CE03-0006 VIP Mont Blanc and the EU ALCOTRA AdaPT Mont Blanc project.The current paper studies the dynamics and age of the Triangle du Tacul (TDT) ice apron, a massive ice volume lying on a steep high-mountain rock wall in the French side of the Mont-Blanc massif at an altitude close to 3640 m a.s.l. Three 60 cm long ice cores were drilled to bedrock (i.e. the rock wall) in 2018 and 2019 at the TDT ice apron. Texture (microstructure and lattice-preferred orientation, LPO) analyses were performed on one core. The two remaining cores were used for radiocarbon dating of the particulate organic carbon fraction (three samples in total). Microstructure and LPO do not substantially vary with along the axis of the ice core. Throughout the core, irregularly shaped grains, associated with strain-induced grain boundary migration and strong single maximum LPO, were observed. Measurements indicate that at the TDT ice deforms under a low strain-rate simple shear regime, with a shear plane parallel to the surface slope of the ice apron. Dynamic recrystallization stands out as the major mechanism for grain growth. Micro-radiocarbon dating indicates that the TDT ice becomes older with depth perpendicular to the ice surface. We observed ice ages older than 600 year BP and at the base of the lowest 30 cm older than 3000 years.Publisher PDFPeer reviewe

Formation processes in the Antarctic snow and superficial firn

第6回極域科学シンポジウム[OG] 地圏11月16日（月）　国立極地研究所３階セミナー

Experimental characterization of the intragranular strain field in columnar ice during transient creep

A digital image correlation (DIC) technique has been adapted to polycrystalline ice specimens in order to characterize the development of strain heterogeneities at an intragranular scale during transient creep deformation (compression tests). Specimens exhibit a columnar microstructure so that plastic deformation is essentially two-dimensional, with few in-depth gradients, and therefore surface DIC analyses are representative of the whole specimen volume. Local misorientations at the intragranular scale were also extracted from microstructure analyses carried out with an automatic texture analyzer before and after deformation. Highly localized strain patterns are evidenced by the DIC technique. Local equivalent strain can reach values as much as an order of magnitude larger than the macroscopic average. The structure of the strain pattern does not evolve with strain in the transient creep regime. Almost no correlation between the measured local strain and the Schmid factor of the slip plane of the underlying grain is observed, highlighting the importance of the mechanical interactions between neighboring grains resulting from the very large viscoplastic anisotropy of ice crystals. Finally, the experimental microstructure was introduced in a full-field fast Fourier transform polycrystal model; simulated strain fields are a good match with experimental ones

Contribution à l'étude du comportement viscoplastique des glaces des calottes polaires : modes de déformation et simulation du développement des textures

The deformation of ice in polar ice sheets implies strain rates lower than 10e-10s-1. The rheology of polar ice is governed by intracrystalline slip and is associated with the occurence of grain growth and dynamic recrystallization. The stress exponent of the secondary creep is lower than 2. A deformation model based on equilibrium between work hardenning and recovery in ice sheet is developed. Hard X-ray diffraction experiments are performed on ice monocrystals taken along the deep Vostok core (Antarctica). The measured lattice distortion can be described by basal geometrically necessary dislocations of screw and edge type. Deformation modes of polar ice are determined by taking into account the mechanical behavior and the arrangement of dislocations. The simulation of the texture development is performed by using the Visco-Plastic Self Consistent (VPSC) "1-site" model developed by Lebensohn and Tomé (1993). This model is modified to take into account the anisotropy of the ice monocrystal, and polar ice deformation conditions. A good estimation of texture development along the Vostok and GRIP ice core is obtained. Expansion of the model to introduce rotation recrystallization does not point out the influence of associated mechanisms on texture development. Finally, a "n-sites" type of modelling using Fast Fourier Transform (Lebensohn 2001) is investigated to simulate the heterogeneities within crystals and improve the calculation of grain interactions.La déformation de la glace des calottes polaires implique des vitesses de déformation inférieures à 10e-10 s-1. La glace se déforme essentiellement par glissement intracristallin auquel sont associés les processus de grossissement normal et de recristallisation dynamique. La loi de fluage se caractérise par un exposant des contraintes inférieur à 2. Les mécanismes physiques qui interviennent au cours de la déformation de la glace polaire sont étudiés par l'intermédiaire d'un modèle physique basé sur l'équilibre écrouissage / restauration. Des expèriences de diffraction des rayons X à hautes énergies sont réalisées sur des monocristaux de la carotte de Vostok (Antarctique). Ces mesures ont permis de caractériser les distorsions du réseau cristallin de ces glaces et de préciser les modes de déformation. Les dislocations géométriquement nécessaires auxquelles sont associées les hétérogénéités de déformation dans les grains sont des dislocations basales de type vis ou coin. Nous présentons une étude de la simulation du développement des textures par le modèle viscoplastique autocohérent VPSC "1-site" de Lebensohn et Tomé (1993). Ce dernier a été modifié afin d'améliorer la prise en compte des caractéristiques de la déformation inhérente aux glaces polaires. Une bonne estimation du développement des textures des glaces de Vostok et de GRIP (Groenland) est obtenue. Le couplage à un modèle de recristallisation par rotation ne permet pas de montrer l'effet des mécanismes de germination et de grossissement des grains sur le développement des textures. Enfin, une perspective est ouverte par une simulation de type "n-sites", le modèle FFT élaboré par Lebensohn (2001), permettant de prendre en compte les hétérogénéités de déformation dans les grains, et les interactions entre grains

Recrystallization Processes in Granular Ice

Recrystallization mechanisms are known to accommodate the deformation as observed along ice cores. The three main processes are classically described as being, successively from the top of the cores, normal grain growth, rotation dynamic recrystallization and migration dynamic recrystallization. Recent observations on local mechanisms at the grain scale tend to question this description. This paper aims at presenting the basic knowledge about dynamic recrystallization processes in materials, with focus on the corresponding mechanisms occuring during deformation of granular ice, more particularly along ice cores. We stress the significance of the scale to consider when analysing the mechanisms, depending on the applications. In particular, we will demonstrate that dislocation substructures can develop locally, due to strong strain heterogeneities, without challenging the classical description that explains the evolution of average grain size and fabrics along ice cores.I. Microphysical properties, deformation, texture and grain growt