8 noded Hexahedron vs. 20 noded Hexahedron

- June 11, 2019 at 2:55 pm
  
  Johnson
  Subscriber
  
  Hi all,
  
  I created a bolted flange connection in Ansys. The calculations were done using one segment of the circular flange down below.
  
  In my first loadstep I apply the preload. Analysing my results I recognized:
  
  - a bolt of 8 noded Hex receives more than the applied pretension (+ more than 10%), refinement helps a bit...
  
  - a bolt of 20 noded Hex receives the correct amount of the applied pretension
  
  Is the 8 noded Hex that susceptible for locking effects, or what is the reason?
  
  Can I add certain key options to get better results?
  
  Thank you!
- June 11, 2019 at 6:21 pm
  
  peteroznewman
  Subscriber
  
  Any simulation should include a Mesh Refinement Study to know that the results are converging to an exact result.
  
  When you change from Hex8 to Hex20, that is like to remeshing with Hex8 elements that are half the size. If you did that, you might find the results are very similar to the Hex20 elements at the original size.
- June 11, 2019 at 8:45 pm
  
  Johnson
  Subscriber
  
  I can follow your thought!
  
  But I actually meshed the model with 20mm Hex8 and 40mm Hex20 and the pretension in the Hex8 is still too high, while the Hex20 is quite exact. Ansys is choosing Keyopt (2) for the Hex8 Solid185, which is the "Simplified enhanced strain formulation". Should I maybe switch to "Full integration with B method"?
  
  Can I insert a command to change to full integration for the bolt?
  
  Thank you
  
  Johnson