PreLoad/ PreTension Bolted connections

Hi there, i just got registered because i couldn't find any topics about how to setup and run FEA with pre-stressed bolt connections.

Is there anybody who already made some experiences with that?

I mean doing this with Nastran is pretty easy but i guess this won't be the same with CodeAster, right?

I can imagine to handle that with a temperature load but i am happy about every single tip on this.

Cheers.

Daniel

Hi,
in this regards Code-Aster is like a free DIY parts shop.
You get all the parts for free, but you must bring your own tools (python) and plan (creativity + engineering knowledge).

How to best model the pre-stess depends on your application. Do you want to model the full bolts in 3D, then you basically have the choice between
a) initial inter penetration and interference fit with contact
b) temperature load (linear analysis possible but additional thermal setup)
c) fictitious clearance (similar to a) but better control)
d) cut + move the bolt shaft (linear analysis possible)

If you want to use some kind of beam/MPC representation of your bolts, there might be many more possibilities.
I would guess that you can reverse engineer the Nastran approach with Code_Aster possibilities quite well.

Do you know how exactly the bolt-prestress is modeled in Nastran?

Best,
Richard

Hi Richard,

thanks for swift response. When the bolted joint is tightened, the loaded portion of the bolt elongates and the bolted medium compresses. However, as the joint is tightened, the actual length of the bolt under load decreases. Therefore, the undeformed length of the bolt defined by the model geometry is larger than the actual length of the bolt under load.

This you have to determine first plates stiffness. There is a procedure in NX-Nastran which works that way:

1. Software first reduces the stiffness of the beam elements that represent the bolts to make their stiffness insignificant. The software applies the Preload force that is specified to the ends of the bolts. The software then performs a linear statics analysis to obtain the relative displacements (U2 and U1) for each pair of nodes and calculates the bolt strains.

2. The software solves the model a second time with calculated strain applied and (optional) service loads.

Thought there might be a similar procedure with CodeAster too. What do you mean by "If you want to use some kind of beam/MPC representation of your bolts, there might be many more possibilities." I think using beams and MPC is an option.
Cheers.

Daniel