Stick-Slip Dynamics of an Intruder in a 2D Annular Bed of Photoelastic Disks

When a granular material is strained elastically, the system may resist granular rearrangement depending on interparticle friction, packing fraction, and surrounding boundary conditions. In these long time-scale "stick" phases, stresses develop in the granular bed until the system yields in a fast time-scale "slip" phase; an example is a slow build-up of stress between sliding tectonic plates and subsequent rapid unloading of stress in an earthquake. We investigate stick-slip dynamics of an elastically driven intruder moving through a 2D annular bed of bidisperse photoelastic disks using high speed imaging of force chains on the grain scale. We analyze both the topology of force networks and the global pressure in the bed to understand force chain self organization and contact rearrangement in slip events once a steady state has been reached. In particular, ongoing work focuses on spatial extent of force chains in front of the intruder and local particle density in its wake at varying packing fraction, interparticle friction, and driving spring elastic constant. Parallel simulations are being studied by E. Goldberg, L. Pugnaloni, M. Carlevaro, and L. Kondic.