Force Distribution and Comminution in Ball Mills
  The motion of granular material in a ball mill is investigated using molecular dynamics simulations in two dimensions. In agreement with experimental observations by Rothkegel [1] we find that local stresses - and hence the comminution efficiency - are maximal close to the bottom of the container. This effect will be explained using analysis of statistics of force chains in the material. 
Volkhard Buchholtz and Thorsten Poeschel