De la pénétration en milieu granulaire

Abstract : The aim of this work is the understanding of the force penetrating in a granular medium. Using force measurements on a cylinder penetrating at constant velocity, this force is found independent of the imposed velocity, proportional to the cylinder diameter and depends non-linearly on the grain size. Besides, the velocity field of the grains has been measured. The flow is found stationary and incompressible. Shear localization is observed close to the cylinder with an exponential spatial dependence ruled by cylinder diameter. An hydrodynamic model based on extended kinetic theory for dense granular flow reproduces well this flow localization and gives force scaling laws in agreement with the experimental results. Defining a granular Reynolds number, we have shown that this regime is equivalent to a Stokes viscous regime for low Reynolds number. A transition to another regime at higher Reynolds number exists where downstream and upstream flows are not symmetrical anymore and both the force scalings changes certainly. At last, the case of the impact of a projectile where these two regimes are present successively is studied both experimentally and numerically. The existence of a supplement force term proportional to velocity square is likely coming from high Reynolds regime. These two terms provide two characteristic times related to the stopping time and adducing arguments for shorter stopping time for high impact velocities.
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Antoine Seguin. De la pénétration en milieu granulaire. Mécanique des matériaux [physics.class-ph]. Université Paris Sud - Paris XI, 2010. Français. ⟨tel-00727081⟩

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