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Statique et rhéologie d'un milieu granulaire confiné

Abstract : A confined granular material leans on walls in order to face external forces. It leads to coupling between mechanical properties of the material and surface properties of walls. This thesis is devoted to the study of this coupling. In a first experiment, we measured the weight at the bottom of a granular material in a column. We defined an experimental procedure such that the material is on the threshold of slipping at each point of the walls. The measured mass saturates with the height of the packing; the saturation mass scales with the radius to the third, and decreases with increasing density and friction at the walls. When an overweight is added on top of the granular material, we observe a maximum followed by a low decrease of the measured mass as a function of the filling mass. This maximum is higher for high density and friction at walls. Janssen's model seems perfectly adapted to describe the unconstrained granular material. However, this model and the OSL model fail to describe the experiment with an overweight on top of the granular material. Isotropic homogeneous elasticity predicts the observed phenomena, qualitatively but not quantitatively. In a second experiment, we pushed the granular column upwards. The resisting force increases exponentially with the height of the packing, which we explain with Janssen's model adapted to pushing. For low velocities, we observe a stick-slip motion, characterized by a maximum force before slipping that increases sharply with decreasing velocity and increasing humidity. We explain this phenomenon with aging of static friction at walls. For higher velocities, we observe a hysteretic transition to steady-sliding motion, characterized by a resisting force increasing with velocity and humidity. The observed phenomena differ for different columns, which proves that the walls properties have a major influence on rheology. A direct measure of bead-wall friction shows similar phenomenology. The study of a polydisperse system of glass beads in a PMMA column shows regular stick-slip motion for very low velocities becoming irregular for higher velocities, with slipping distribution getting larger for small values.
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https://tel.archives-ouvertes.fr/tel-00001963
Contributor : Guillaume Ovarlez <>
Submitted on : Wednesday, November 13, 2002 - 2:47:32 PM
Last modification on : Tuesday, December 8, 2020 - 3:39:39 AM
Long-term archiving on: : Friday, April 2, 2010 - 6:20:20 PM

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  • HAL Id : tel-00001963, version 1

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Guillaume Ovarlez. Statique et rhéologie d'un milieu granulaire confiné. Dynamique des Fluides [physics.flu-dyn]. Université Paris Sud - Paris XI, 2002. Français. ⟨tel-00001963⟩

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