How can I fill a piece with 3D polyhedrons like cubes or hexahedrons (I mean like honeycombs)?
Cubes would be easy. Just cut a cube from the center of the part and then use a series of patterns to create a 3D grid of the cube cuts. If you wanted to keep a solid wall on the outside of the part then first copy the body, perform a shell on one of the bodies, then do the 3D grid of cube cuts to the other body, then merge the two bodies. An alternative to patterning a cube cut would be to model a solid cube body, then pattern the body across the part, then do a Combine>Subtract to remove the cubes from the main body.
For other polygons you can use the same method, although you will need to pattern in more directions. I don't know of a more straightforward way.
You might consider doing a search on "polyhedrons polyhedra Rhino3D"
or this.. RhinoPolyhedra | Rhino
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