Jean Rajchenbach

Response of a cohesionless packing to a point load

In order to study the mechanical behaviour of grain piles, we investigate the response of a non‐cohesive two‐dimensional packing of cylinders submitted to a localized force, that in the reversible regime of deformation. By means of image processing, we obtain an accurate measurements of the individual grain displacements. The measured displacement field deviates unambiguously from the predictions of linear continuum elasticity. Instead, the data reveal a localization process, as well as a partial agreement with the diffusive models of Harr (1966) or of Coppersmith et al. (1996).

Mechanichal Behavior of a Noncohesive Packing at Small Deformations: Deviation From Continuum Elasticity

In order to specify the mechanical behavior of grain piles, we investigate the response of a non‐cohesive bidimensional packing of cylinders submitted to a point load. By means of image processing, we have an accurate access to the individual grain displacements in the reversible regime. The measured displacement field deviates unambiguously from the predictions of Continuum Elasticity. The data reveal a partial agreement with the diffusive models of Harr (1966) or of Coppersmith et al. (1996).

Photoelastic study of acoustic wave propagation in grain packings

By means of photoelasticity, we success in visualizing in real time the propagation of acoustic waves in a granular packing of cylinders. As previously mentioned by Nesterenko [1] for the case of spherical grains, the nonlinearity of the contact law between grains induces a dependence of the wave velocity both on its amplitude and on the confinement force. Our experimental procedure allows an access to the local state of stress of individual grains as a function of time with a good accuracy. Our results concerning the wave velocity as a function of the amplitude, and of the confinement force, are compared to theoretical predic tions and to the spherical beads case.