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Anaïs Abramian (d'Alembert) - From soda cans to granular columns : two examples of collapses

Séminaire général
Date: 2021-02-11 11:30

In this talk, I will present two different mechanical systems which have in common only the name : the collapse. 

First, I will focus on the collapse of a cylindrical shell. When we compress a cylindrical shell from its top, it remains stable over considerable weights until it eventually buckles at a critical load. The shell then deforms and looses all its useful mechanical properties. What controls this critical load is complex : it stochastically varies from one can to the other because it strongly depends on the shell’s imperceptible defects; it thus remains unpredictable without a prior knowledge of these imperfections. Here, we propose an alternative approach to measure this load. We show that this instability can be triggered by a perturbation of finite amplitude, and, by probing the shell close to a defect, we can measure its buckling load without damage it.

Then, I will present the collapse of a cohesive granular column. Cohesion forces strongly alter the flow properties of a granular material, and the collapse is a simple configuration to start investigating this influence. It consists in an initial pile of material which is released, and then flows under its own weight. Experiments show that the length of the final deposit is shorter, and the flow slower, as cohesion increases. To model this behaviour, we adopt a numerical approach. We implement a peculiar rheology in a Navier-Stokes solver (Basilisk) : the so-called µ(I)-rheology, usually used for dry granular materials, supplemented by a yield stress for cohesion. With this approach, we recover the stability of the column, and the collapse dynamics at first order. To reproduce the roughness of the deposit observed in the experiments, however, we need a grain-scale numerical approach, as Contact Dynamics.

 

 

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  • 2021-02-11 11:30