Sean McNamara

Avalanche precursors are small, quasiperiodic surface displacements observed experimentally during the slow inclination of a granular bed. In spite of being studied experimentally since the mid-2000s, they have eluded numerical models. One recent contribution is a one-dimensional model where a line of sliders linked by springs is placed on a slowly inclined frictional plane. In this paper, we present a two-dimensional model that stands between this one-dimensional model and the three-dimensional experimental setup. In our model, disks are placed on a frictional plane, and interact with their neighbors and boundaries with typical granular molecular dynamics interactions. The model robustly produces quasiperiodic compaction events. The angular period (change in inclination between two events) is proportional to the difference between the static and dynamic friction coefficients. The first event occurs systematically earlier than predicted by the coefficient of static friction: The inclination can be predicted by subtracting the angular period from the static friction angle. The inclination at the initial event and the angular period decrease for large systems. When the inclination is varied cyclically, longer sequences of events can be observed, as in recent experiments. Finally, the relation between the observed compaction events and avalanches and avalanche precursors are discussed.

EPJ Web of Conferences, open-access proceedings in physics and astronomy

EPJ Web of Conferences, open-access proceedings in physics and astronomy

We present a numerical implementation of an active inclusion in a granular material submitted to a biaxial test. We discuss the dependence of the response to this perturbation on two parameters: the intragranular friction coefficient on one hand, and the degree of the loading on the other hand. We compare the numerical results to theoretical predictions taking into account the change of volume of the inclusion as well as the anisotropy of the elastic matrix.

A reformulation of the statistical mechanics of granular materials replaces the volume of the material with a function related to its structure.

The elastic coupling between plastic events is generally invoked to interpret plastic properties and the failure of amorphous soft glassy materials. We report an experiment where the emergence of a self-organized plastic flow is observed well before the failure. For this we impose an homogeneous stress on a granular material, and measure local deformations for very small strain increments using a light scattering setup. We observe a nonhomogeneous strain that appears as transient bands of mesoscopic size and a well-defined orientation, which is different from the angle of the macroscopic frictional shear band that appears at the failure. The presence and the orientation of those microbands may be understood by considering how localized plastic reorganizations redistribute stresses in a surrounding continuous elastic medium. We characterize the length scale and persistence of the structure. The presence of plastic events and the mesostructure of the plastic flow are compared to numerical simulations.