Successive reintrusions in a granular medium

Abstract

We measure and analyze the drag force experienced by a rigid rod that penetrates vertically into a granular medium, partially withdraws before sinking again. The drag during the successive reintrusions is observed to be significantly smaller than the force experienced in the first run. Two force regimes are evidenced depending on how the re-intrusion depth compares with the withdrawal distance ∆. These two regimes are characterized by a force curve of positive and negative curvature and are separated by an inflection point which is characterized experimentally. We approach the difference between the first intrusion and the following re-intrusions by considering a modification in the stress field of the granular material after the partial extraction of the rod. A theoretical model for the stress modification is proposed and allows to rationalize all the experiments realized for different withdrawal distances ∆. This framework introduces a crossover length λ above which the stress modification in the granular medium is maintained and that is shown to depend linearly on ∆. Finally, the model provides a prediction for the location of the inflection points in reasonable agreement with observations.

Finite size effects during the penetration of objects in a granular medium

“…21 Other parameters like the preparation of the packing 25 or the number of cycling of the motion also modify the penetration forces. 26 A second non-trivial important result is the existence of a lift force on an object moving horizontally in grains, even if the object is symmetrical, an effect explained by the presence of the gravity-induced pressure gradient, which breaks the top/bottom symmetry. 27,28 More generally, the shape of the object and the direction of its motion relative to gravity influence the total force experienced by the object.…”

“…21 Other parameters like the preparation of the packing 25 or the number of cycling of the motion also modify the penetration forces. 26…”

Force model in the penetration by impact into confined granular media

“…They are also a function of the packing fraction of the medium. The determination of these coefficients has been the subject of numerous studies [7,19,30,[33][34][35][36].…”