how to pretension a bolt?

[maker9876]

Does anyone have any recommendations about how best to pretension a bolt in static analysis?

For example suppose that object A is bolted to object B with bolt c and nut d....

Normally one would want to apply "separation + sliding" contacts between all smooth surfaces and "bonded" between threaded surfaces.

Then what next? How to set up the pretension?

(When I understand how to do this in general, would like to apply it to a tapered rod inserted into tapered hole in a block, held in place by a tensioned bolt inserted axially. Hmmm....)

[Anonymous]

For the analysis, maybe branch your file to a new copy for safety (in case you somehow lose history), then in that copy unite or combine the bolt to the material it is is bolted to, thus creating effectively a solid that includes the bolt. Then analyse the combined solid... not perfect, but closer perhaps...

[maker9876]

Normally with this kind of thing each item is a Component. The components are assembled using either Joints or "As built joints". Then Contacts are defined between the touching (or potentially touching) faces of the components. For example "bonded" or "separation + sliding". Then loads are applied as Forces, Pressures, Moments or other.... The question is really how to combine these various elements to simulate a pre-tensioned bolt. Maybe somebody has done it and knows?

[brianrepp · Accepted solution]

@maker9876 - I think what you're looking for is what we're calling "connectors" and will likely be available later this year.  In the interim, you could also sign up for Project Arro, a simulation preview here.

[maker9876]

Thanks. Sounds quite exiting. Have applied to Project Arro.

[Anonymous]

Hi @maker9876, I had this same question, and was basically told that you can't. However, I think I've found a roundabout way to do it, although in my case I wasn't worried about including a nut in my analysis. Anyway hear me out.

If you know the material properties of the bolt, and how much pre-stress it's meant to have, then you can calculate how much the bolt would stretch from said pre-stress. Then you can apply this stretch as a prescribed displacement to the bolt, from the constraint menu. You can verify it by solving it before applying loads. The results will show you the pre-stress in the bolt. Once you're happy with that, go ahead and add your loads, and solve!

It's a little bit of mucking around to work out the displacement initially, but once you've got that sorted, it's pretty solid. The hardest bit for me is finding proper detailed data on the bolt material. If you've got any good resources that you can point me towards, it'd be really appreciated!