Pre-tension 1

[Kottier]

I'm modelling a bolted flange and have to pre-load the bolts.
In the past I used temperature dependent properties in order to obtain an specific pre-tension force.
But I've read something in the help about specific pretension elements. Are they easy to use or would it be wise to stick with the temperature?
Has somebody any expierence or advice.

Thanks

 

[Drej]

Whatever's easiest for you. I've used both the temp shrinkage method and the PRETS179 elements. Once you've got it setup, I think the PRETS179 method is more convenient, and it saves you a few iterations in achieving your pre-load force (with the shrinkage method, of course, you have to carry out a few iterations - for big models this can be difficult). There is a really useful example in the help file on using pretension elements - see Basic Guide> Chapter 2. Loading> 2.9. Defining Pretension in a Joint Fastener.


-- drej --

 

[Kottier]

Thanks Drej,

I hoped it would save me a few iterations, so that's great.
Only one question remains for me, what causes the need for iterations.
Why does the bolt-force change when the temp method is used, is it because the deformed shape of the bolt changes the shrinkage. Or are their other influences.

 

[Drej]

Yes, as you say you need to iterate with the shrinkage method because of the (usually) unique geometry of each bolt/other components as well as load paths, mechanical properties, etc. etc.. Because these properties are usually different for each analysis, you need to repeat the procedure to achieve the correct preload.

Cheers,

-- drej --