**Shaken**** sand, stress and test particles **

**J. Villain** ,
Theory group, ESRF, 6 Rue Jules Horowitz, 38000
Grenoble; **jvillain@esrf.fr**

**Abstract :**

*The definition of a stress tensor in shaken granular materials is difficult
because the local properties
change much in space and
time. It is shown that in a stationary
regime a definition of a
standard form can be given at
least in the case of a simple geometry (parallelepiped container, infinite
along two dimensions, no symmetry breaking). In that case the stress is shown to be uniform.
The quantities P+ and P- introduced
by Evesque are found to be
relevant to describe the force acting on a heavy test particle.*

**Pacs # : 5.40 ; 45.70
; 62.20 ; 83.70.Fn**

*poudres** & **grains***20** (2), 29-36 (Juillet 2012)