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Nonlinear waves in granular packings

- Leader : Rajchenbach Jean

- Collaborators within the LPMC : Noblin Xavier

- External Collaborators : Job S. (SupMeca, Paris)

- Description :

The noncohesivity of granular media, the disorder in the intergrain force network, the nonlinear nature of the contact forces are at the source of the numerous ill-understood and original behaviours exhibited by the propagation of sound waves in granular packings. As established by Hertz (1885), the normal contact force between two elastic spherical grains varies as a power 3/2 of the distance between the centroids. For a one dimensional array of spherical grains, Nesterenko (1984) theoretically predicted that two different types of elastic sound waves can propagate through the medium : i) ordinary sound waves, for small amplitude excitations, with velocities dependent on the confinement pressure and ii) nonlinear waves, for larger amplitude excitations. The nonlinear wave is of solitonic type, and has been previosly studied by Nesterenko and Lazaridi (1985), Coste et al. (1997), et Job et al. (2005). We conduct experiments aimed at studing the nonlinear and the interference properties of acoustic waves in one-, two-, and (in the future) tree-dimensional packings of grains. Using the photoelastic properties of the grains, we succeeded in visualizing in real time the propagation of the deformation waves in one- and two-dimensional packing of cylinders. In particular, we pointed a cross-over in the sound velocity as a function of the confining static force. For small static forces, the sound velocity is mainly governed by the rugosity of the surfaces in contact at the microscopic scale ; for larger confining forces, the velocity is detrermined by the macroscopic geometrical properties of the interfaces.

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Fluides & Matériaux Complexes, Fluides Complexes, MIMIC