Contact: Test Model

Aftab

Hi Everyone,
I’m working on developing a typical contact model (very small model) for a bolted-type connection. In some unique situations, this approach might be necessary to determine the ultimate capacity of the connection. This is a test model designed to simplify the elements, as performing a single bolted connection analysis is uncommon.
Could you please verify whether the level of contact displacements is acceptable? It seems there’s a 1mm indentation of one surface into the other. Additionally, the model fails to converge if I set the normal stiffness per unit area to more than 900 GPa/m. Typically, the bolt would fail under this level of stress; however, I’ve set the bolt material to behave elastically in this case.

Your suggestions and feedback are greatly appreciated.

Sergio

In my opinion the level of penetration in the plate to plate contact area is too high with your model set up. I have changed the contact between bolt head and plate to a basic TIE, and increase a lot the contact stiffness (up to 16000 Gpa/mm) and get much less penetration. Also have removed the contact bc between bolt shaft and hole, there is no contact there, and the step increment changed to a fixed 0.05 seg (20 increments for the whole simulation).

Aftab

Thanks Sergio, for looking into this. This is much better. I may need contact between the bolt body and the hole to transfer the shear in real connection. However, it may be a good idea to use a tie between the bolt head and the plate. Much appreciated.

Sergio

If you think that there will be contact between de bolt body and hole, then you need to apply contact with separation at the two bolt and nut heads and plate to allow the slippage, otherwise the TIE will prevent the internal contact. Also add the bolt preload.

But that kind of lateral movement of the bolt only happen at very high loads and only if the bolted union was not well designed.

Aftab

Thanks Sergio, i don't think that there is huge difference between the two solutions, somehow the contact between bolt head and the plate do not well converge. How would apply a bolt pre-load?

Sergio

There is a specific boundary condition in Mecway/CalculiX called Pre-Tension Section

Aftab

Much appreciated Sergio.