ABAQUS model of polycrystal plasticity

Hi everyone 

I am learning the polycrystalline crystal plasticity and testing material in ABAQUS and UMAT. Now I am trying to build a RVE by using the truncated octahedrons as the grain shape or Voronoi tessellations.

For truncated octahedrons, I built a truncated octahedrons and assembled them into the grain aggregate in the .inp file, and assign orientations in the UMAT based on the part's name. However, I found it hard to define their interaction between grains. What is their interaction properties and how to define the contact pair in an automatic way?

For Voronoi tessellations, if I have the vertices coordinate for each voronoi polygon, I have no idea how can I assign orientations to each grains. And how to mesh each grains, it should be done by importing the geometry to ABAQUS and mesh the geometry in ABAQUS, or mesh using other software and then import into ABAQUS?

Lu