Propagation of sound waves in cohesionless granular packings presents original and complex behaviors due to the divided nature of those materials. Such medium display disordered and nonlinear properties. Our study is original because we use photoelastic cylinders. By means of a fast camera, we visualize the deformation field associated to the sound wave propagation. Moreover, we probe a contact law different from that of spherical grains. We study in 1d and 2d the role of grains roughness on the propagation of sound wave in granular media using photoelasticity. Thanks to our technique, we can directly visualize it. 

    With G. Huillard and J. Rajchenbach.

  First we are interested in the simplest granular packing : a one-dimensional array of cylinders in contact. We carry out an experimental investigation concerning the propagation of an acoustic pulse, in both cases where the pulse amplitude is small (linear wave), or large (nonlinear waves), compared to the static confining force applied to the chain.
In the first case, we prove the prominent role played by the imperfections of the contacts on the sound celerity. We also show that the pulse damping mainly originates from dry friction.
In the case of very large amplitude, the initial pulse breaks down into a wave train of decreasing amplitudes, with a width comprised between 3 and 4 grains and asupersonic speed. This speed, in units of sound celerity, depends only on the ratio of the amplitude to the static confining pressure. These observations are interpreted by generalizing the results of Nesterenko.

In this movie (1.7 Mo) we show a linear wave observed in false color by photoelasticity at 90000 fps. Real time : 2ms, slow down 10000x.
In this movie (1.9 Mo) we show a nonlinear wave observed in false color by photoelasticity (static force 1N, wave amplitude 52 N).

  We also study the case of the two-dimensional packings. Linear sound waves propagate through the static force chains and their velocities increase with the static force in the chain.