Simulating Bolts in Analysis 2

[6060842]

Hi everyone,

Can anyone give any guidance in simulating bolts within an FEA analysis?

I have seen some FEA reports of brackets bolted to stiff structures(ship/train walls),where instead of modelling the wall structure and bolts, they have simply included the bracket and assigned a fixed restraint on the inner surface of the hole in the bracket the bolt would pass through. I would have thought defining a split line around the hole, the diameter of the bolt/washer, would have been more appropriate.

Anyway I just wanted to gauge what othe people did

Many Thanks

Tom

 

[Stringmaker]

There are many ways which bolts can be represented as you already know. The spectrum is broad, anywhere from applying a simple constraint to a bolt hole or fully fixing it to modeling the bolt and the applicable preload. It's really dependent upon what the scope of your analysis is.

Most of the work I do deals with preloaded bearing stacks or bolted flanges so typically the bolts or retaining elements are modeled and preloaded. However, in many cases I will simply fix the ID of a bolt hole if I only am concerned about the impact on the structures stiffness being constrained by the bolt rather than stresses in that regions.

This topic really isn't that complex and really is dependent on what you want to get out of your analysis. Use your best judgement.

Good luck!

 

[rb1957]

typically i've seen the joint is modelled as though it were welded together, and follow-up with a hand calc redistributing these shears and moments onto the fasteners. you can model the fasteners if you've got tons of computing space and time or a particular concern.

 

[GregLocock]

Don't know about bolts but for spot welds the body guys use a macro that sets up a bunch of springs and other elements at each spotweld. Something like 30 of them.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[corus]

At one extreme you can just ignore the bolts and bolt holes completely and simply assume your structure is continuous, if you're more interested in regions away from that area. At the other extreme I have applied a compressive load within the washer diameter and allowed contact between the joining surfaces to be formed. This is a better way to tie the surfaces together rather than assume a spot weld type connection as the area that is effectively tied together will extend much further away from the bolt hole itself, depending on the preload within the bolt. Some software will also allow a beam type connector (the ends tied to the bolt hole inner diameter) for which you can define a preload to clamp the surfaces together through contact. It's basically the same idea as applying a pressure to the bearing surface of the washer, though I'd treat the results at the bolt hole itself with caution.

It all depends on how far you want to go, or need to go, in modelling the bolt.

corus

 

[EdDanzer]

Search this forum as this topic has been covers a few times.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[MrVessels]

6060842

The following might be a useful reference for you.

Method of Modeling Bolts in the Bolted Joint by Jerome Montgomery.

MrVessels

 

[6060842]

Mr Vessels,

Thank you very informative

Tom

 

[BATman2]

6060842,

I would stick with hand calculations for the fasteners and then testing if the joints/loading in question is complicated.

There are many factors to consider that you may or may not capture in your model, it will only be as good as your assumptions. Unless you know all the details (environment, loads variations, bolt quality, etc.) you will need to ensure a reasonable factor of safety is built in. At that point, the benefit of detailed FEA is probably lost for a "standard" joint /bolt.

Also see:

http://www.boltscience.com

Batman2