Force distributions in 3D granular assemblies: Effects of packing order   and inter-particle friction
  We present a systematic investigation of the distribution of normal forces at the boundaries of static packings of spheres. A new method for the efficient construction of large hexagonal-close-packed crystals is introduced and used to study the effect of spatial ordering on the distribution of forces. Under uniaxial compression we find that the form for the probability distribution of normal forces between particles does not depend strongly on crystallinity or inter-particle friction. In all cases the distribution decays exponentially at large forces and shows a plateau or possibly a small peak near the average force but does not tend to zero at small forces. 
Daniel L. Blair, Nathan W. Mueggenburg, Adam H. Marshall, Heinrich M.   Jaeger, Sidney R. Nagel