The problems of solid fractures and granular media have occupied physicists and engineers for centuries. These phenomenons are classically addressed within the framework of continuum and discrete mechanics. Still, in both cases, stress concentration at the local scale along with intrinsic microstructural heterogeneities make the observation at the global scale dramatically dependent of the very small scale. This yields peculiar statistical behaviour known as earthquake dynamics. In the case of fracture, we designed an experimental setup that allows growing well-controlled tensile cracks in brittle heterogeneous solids of tunable microstructure. This allowed us to characterize quantitatively the crackling dynamics of cracks, also to evidence intriguing statistical similarities between the seismicity associated with this simple situation (single crack under tension) and the much more complex situation of multicracking in compressive fracture and in earthquakes. In the case of granular materials, we experimentally study the deformation of a three-dimensional sphere packings subjected to macroscopic deformation. We address the non-linear force response of a disordered packing under compression, force network dynamics and explore the statistics of plastic rearrangements inside cyclically loaded packings.
Thursday, September 4, 2014 - 11:30am