Reflection and Exclusion of Shear Zones in Inhomogeneous Granular   Materials
  Shear localization in granular materials is studied experimentally and numerically. The system consists of two material layers with different effective frictions. The presence of the material interface leads to a special type of "total internal reflection" of the shear zone. In a wide range of configurations the reflection is characterized by a fixed angle which is analogous to the critical angle of refraction in optics. The zone leaves and reenters the high friction region at this critical angle and in between it stays near the interface in the low friction region. The formalism describing the geometry of the shear zones and that of refracted and reflected light beams is very similar. For the internal visualization of shear localization two independent experimental techniques were used (i) excavation and (ii) Magnetic Resonance Imaging. 
Tamas Borzsonyi, Tamas Unger, Balazs Szabo, Sandra Wegner, Frank   Angenstein and Ralf Stannarius
cond-mat.soft