Buckling of a rod penetrating into granular media
Résumé
We investigate experimentally the possible buckling of a thin rod when penetrating downwards into a granular packing. When its bottom end reaches a specic depth, the rod may start buckling provided that the embrace is not enough to stop that phenomenon. The critical rod depth zc at buckling is observed to scale with the rod length L either as 1/L or 1/L 2. These two scalings are shown to arise from the two resistant force terms that come into play during the rod penetration : a pressure force at the bottom of the rod that increases linearly with depth and a frictional force on the rod side that increases quadratically with depth. At the buckling point, the destabilizing force corresponds to the expected value given from conventional Euler's critical load for a rod bottom end considered as xed in the granular clutch. Finally, we draw a buckling/non-buckling phase diagram in a parameter space given by the rod aspect ratio and a rod/grain stress ratio.
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