Pre-stress on screw

[S3N9]

Hi all,

Regarding the way of establish pre-stress as follow:

Let the screw component (e.g. head or thread) penetrate into the connected steel sheets for a certain pre-calculated depth,
during the first load step, penetrated component will be pushed back due to the contact elements introduced earlier,
thus creating a compressive force between 2 connected sheets.

Is it practical, or in my concern, is it possible for most FE software? I am using LUSAS.

Thank you all in advance.

 

[flash3780]

What you described, adjusting the contact penetration, is indeed one way to model bolts. Depending on what you're trying to get from your model, there are less complex methods which can produce acceptable results. Here is a document from ANSYS which describes various methods of modeling bolts:

http://ainastran.org/staticassets/A...elibrary/confpaper/2002-Int-ANSYS-Conf-38.PDF

The options will vary between software packages, depending on how much control they allow the user to have (I'm haven't used LUSAS, but it seems pretty capable). Often, hand calculations are sufficient for most bolted joints. For thinner flanges, things like flange waffling and the like may need to be simulated, but a simpler method may be sufficient. Personally, I think that using tension only elements with a specified initial strain seems clever.

 

[S3N9]

Thank you very much, flash3780.

Would you mind explain the flange waffling? I think it would be useful for me, as my test subject also included thin-walled steel sheet.

 

[flash3780]

Flange waffling (not sure if there's a more appropriate technical term for it) can occur if your bolts are spaced too far apart from one another. If you're living within design codes, it's not an issue. However, if you are designing a joint with a a lot of space between the bolts, a thin flange, or that is otherwise oddly shaped, you may be concerned with whether the flange will deform enough for the joint to separate and leak between the bolts.

 

[S3N9]

Thank you for your help