Ansys anti sliding preload bolt

[gianlucaforza86]

Dear all,
i need your help about a simulation on Ansys mechanical. I attached an overview about the simulated case. In this case I have 2 clamps. Linked to this clamps there's a point mass of 140 kg (not visible on the picture). I should tighten the bolts to increase the friction beetween the round pipe and the clamps. Additionally I shoudl calculate the minumum preload to avoid clamp rotation.
In my simulation there are 4 frictional contacts beetween the clamps and the round pipe, and a fixed supports on the pipe faces. The problem is that the system is not fully constrained (ansys error).
How could I proceed?
How could I calculate the min, bolt preload to avoid clamp sliding?

I thank you in advance for the support.
Gianluca.

 

[MegaStructures]

Check your contact conditions between the pipe and clamp and bolt/clamp. I don’t use ANSYS, but NASTRAN doesn’t allow friction to be used as a constraint, meaning if friction is the only thing stopping rigid body motion it will throw an error.

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”

 

[gianlucaforza86]

Thanks for the reply but in the reality the friction could be a constraint, so it should be possible.

 

[human909]

How could I calculate the min, bolt preload to avoid clamp sliding?

Why does this need to be an FEA problem? This seems to be a pretty basic statics problem. From what I can see FEA just complicates things, in what could be otherwise a first year engineering exam problem. Don't get me wrong, I love using tools like FEA to make my life easier. This does not seem to be one of those cases.

Lets see if I can still pass first year engineering:

[Bolt tension] * [2(number of bolts)] * [2(normal force acting in opposing directions)] * [conservative coefficate of friction] / [safety factor]

This is my code agnostic response, your locality may present something different but I'd be happy with this for most applications.

 

[gianlucaforza86]

yes, you have right. I will proceed with manual calculations. Thanks for the advice!!

 

[MegaStructures]

"In-reality" and what the FEA solver allows are two different things. Again, I don't use ANSYS so I can't tell you for sure.

It seems like you might be new to FEA. I agree that manual calculations are better here, but for learning I would complete the manual calculations and then revisit the FEA to try to match up answers. If you get a completely different answer in the FEA model you're doing something wrong.

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”