Nonlinear Static - Modeling cylindrical joints with separation contact

[Anonymous]

Hello,

I’m working on a simplified model of a cylindrical joint.
Pin and holes were modelled without interference in CAD.
The two ends of the pin are fixed.
The counterpart is rotated at the end by a moment.

I tired different contact settings but achieved no satisfying results.

The attached pictures show a setup with symmetric separating contacts.

When looking at the result you can see, that there are sharp stress peaks.
Thus, I don’t think I could use these stresses for dimensioning of the geometry.
Furthermore, the contact status and pressure shows no continuous progression.

Does this occur because the geometries interfere after meshing (like mentioned here: https://knowledge.autodesk.com/support/nastran/learn-explore/caas/sfdcarticles/sfdcarticles/How-to-p...)?
When Nastran modifies the position of the interfering slave nodes position, does this result in stresses?
How could I solve this problem to get accurate stresses in the contacting areas?
Is there a better way to model a cylindrical joint?
Is it advisable to disable the position modification, by setting NCONTACTGEOMITER to 0?

Thanks for your help!

Greetings

Sven

[John_Holtz]

Hi @Anonymous 

Sorry for the delay. Just looked back through the list and saw that no one had replied yet.

What do you mean by "could use these stresses for dimensioning of the geometry"? Are you trying to determine if you should design the parts for 0.003 mm clearance or a 0.1 mm clearance? Or are you trying to determine the amount of interference that you want? If you are trying to do either of these, then you need a very, very fine mesh on the two surfaces. Maybe try making the mesh 5 times smaller on the contact surfaces. (Alternatively, you can do a hand calculation of the Hertz contact stress size and base the element size on that.)

Also, it may help to use more steps in the analysis. Try 50 steps.

Final thing. Have you ever looked at a Nastran (.nas) file? It is not easy. Please provide a pack and go of the Inventor file in the future when you want to include the model.