Mario Alberto Annunziata - CNR ISC Roma	#
Friction law(s) in granular materials # 	
Granular materials are present in many aspect of our lives. Let us think 
of sand, pills, nuts, rice, powder, builiding materials, cereals for 
breakfast just to make some examples. All of them borrow some features 
from solid, liquid and gaseous state so that they act as they were a 
'fourth' state of matter. Furthermore, they can exhibit collective 
phenomena and their phase diagrams are often phenomenologically rich and 
non-easily predictable. The knowledge of the friction law of sheared 
granular materials is thus important for speculative and also practical 
reasons, like packing or transport problems. We did extensive Molecular 
Dynamics simulations of mono- and bi-disperse granular mixtures under 
different types of shear and found that friction law has some universal 
features which depend only on the properties of granular constituents, 
while other dynamical features depend on the way the shear is done.