The effect of contact torques on porosity of cohesive powders
  The porosity of uniaxially compacted cohesive powders depends on the applied stress (including gravity). The case, where these stresses are weak, is considered. The compaction results in a porosity which is a function of sliding, rolling and torsion friction. By contact dynamics simulations it is shown that the influences of contact torques (static rolling and torsion friction) on the porosity are significant and approximately additive. The relevance for nano-powder pressure sintering is discussed. 
Guido Bartels, Tamas Unger, Dirk Kadau, Dietrich E. Wolf and Janos   Kertesz