I have two hollow cylinders standing on top of each other axially. The faces in contact with each other have a very shallow, very wide chamfer. The bottom cylinder is sitting on the ground, and I apply a 2000# force to the top cylinder (axially downwards). I want to see if/how much the chamfers between the cylinders deform. I think this should be really straight-forward, but when I try to run the analysis I get an error stating that "The solver has numerical difficulties. Model may not have adequate fixtures".

My only physical constraint is the floor that the bottom cylinder is sitting on. I've tried to model this with:

- a roller/slider fixture on the bottom face
- a fixed geometry fixture on the bottom face
- an advanced/flat face on the bottom face with the normal translation set to 0
- an advanced/reference geometry on the bottom face with an axis to define the direction and the translation set to 0
- by creating a coincident reference plane on the bottom face and setting it as a virtual wall.

I get the same error for all but the fixed geometry. For that I get incorrect results - deformation in a circular motion, mainly to the positive-x direction. I also have the global contact set to no penetration instead of bonded, because that's how the parts really are. But I've also done it bonded, and gotten the same error.

I'm sure this is just a stupid error on my part. If anyone has any suggestions, I'd really appreciate the help. Thanks so much.

There are a few things you need to do to make this work. First, it sounds like you have a point/line contact between two parts. You cannot reasonably do this in FEA. If you must make a sharp edge contact another body, add a small flat edge to cut off the sharp point.

If the two cylinders are identical (the area of interest anyway) then only model one cylinder against a solid wall (for a linear analysis this will do the same thing.

Assuming the identical cylinders you can now take a single model, cut a flat spot on the chamfer, use a spring constraint on the cylinder wall (value can be quite large like 100-1000lb/in2) then make a sliding contact on the flat face and force load on the top/bottom of cylinder. This will give you the most accurate result acievable with a linear static analysis.

Edit: I created this part doing what i think you are trying to do although to get the results you are looking for I reversed the load and contact. This makes no difference for the study since a linear analysis will follow the rules of statics to the "t".