Mechanics of Arctic sea ice and granular materials : two media, two approaches

• Main Author: Gimbert, Florent
• Other Authors: Institut des Sciences de la Terre (ISTerre), Centre National de la Recherche Scientifique (CNRS)-PRES Université de Grenoble-Université Joseph Fourier - Grenoble 1 (UJF)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement IRD : UR219-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry ), Université de Grenoble, David Amitrano, Jérôme Weiss
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2012
• Subjects: Localization; Fracture; Granular materials; Sea ice; Strain; Localisation; Rupture; Milieux granulaires; Déformation; Banquise; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Arctic; Arctic Basin; Arctique*; banquise
• Online Access: https://tel.archives-ouvertes.fr/tel-00846380; https://tel.archives-ouvertes.fr/tel-00846380/document; https://tel.archives-ouvertes.fr/tel-00846380/file/30375_GIMBERT_2012_archivage.pdf

Two approaches to study the mechanical behaviour of Arctic sea ice in one hand, and of granular media on the other hand, are presented in this thesis. First, a continuum mechanics analysis is conducted on sea ice in order to extract the relevant physics that, to the first order, explains the observed recent acceleration of sea ice drift and deformation. An original method to determine the mechanical properties of the sea ice cover at large time and spatial scales, i.e. over the whole Arctic basin and over 40 years of record, is proposed by quantifying the amplitude of inertial motion of ice drifters. This method allows to estimate an average ice cover friction, that is currently not accessible through other means at those large spatio-temporal scales. We show that a genuine mechanical weakening of the Arctic sea ice, associated to changes in the degree of fragmentation of the ice cover, comes into play to explain the observed changes in terms of sea ice kinematics and dynamics. This underlines the necessity to take into account this component in modelling studies, as well as to develop specific tools to measure an internal friction at local scales. Second, a statistical mechanics analysis is adopted in order to characterize the mechanical heterogeneities associated to the macroscopic behaviour of frictional granular materials submit- ted to compressive loading. From numerical modeling and experimental studies, quantitative estimates of heterogeneities that develop in the shear stress and strain fields are provided. At short timescales, intense stress and strain localization is reported, associated at the macrosco- pic instability to specific multi-scale properties. Thus, at this flow instability, these strain field properties significantly differ from the shear band formation observed after the instability when considering large time scales. The connection between these two characteristic features remains to be understood. Dans cette thèse, deux approches de caractérisation d'un comportement mécanique sont ...