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Subject: Re: [struct] Bolt Stress Concentrations
Author: John Ceko
Date: 2003-04-25 09:30:00

Geoff,

A few thoughts:

Your results aren't surprising. A fastener will generally fail in one of
three locations: fillet between the head and the shank, first engaged thread
and the thread runout at the shank. If you have a custom fastener, then you
can add other locations with changes in dia, etc.

I would argue that if your bolt preload was anywhere near the proof load,
that there will be small local areas of plasticity. That doesn't necessarily
mean the bolt will fail. As Marco has already mentioned, a properly designed
bolted joint should have small alternating loads on the bolt itself. When
you talk about failure, do you mean failure in fatigue or static loads? The
endurance limit for a fastener can be 10% of the ultimate strength, because
of all the stress concentrations.

As far as failure criteria, depending on your application, the spec VDI 2230
is pretty good for machine type applications. For fatigue, they basically
ignore mean stress effects (for a given range of preload), and provide
limits on the alternating load. For a more civil structural side, Eurocode3
or the AISC Manual of Steel Construction, Load and Resistance Factor Design
(LRFD) would be more appropriate. They look at bolted connections as
analagous to a weld, and they provide allowable stress ranges for different
details. I had a pretty frustrating web search on this topic, so hopefully
your luck will be better. Maybe some of our civil colleagues could describe
it better than I can.

A typical approach is to extract the loads from the FE model and then check
those against whatever codes/allowables you use.

Hope that helps.

John Ceko P. Eng.
HUSKY Injection Molding Systems
Index Advanced Engineering
560 Queen St. S.
Bolton, Ontario, Canada, L7E 5S5
Tel. (905) 951-5000 ext. 3347
Fax (905) 951-5365
Email: jceko@h...

-----Original Message-----
Sent: Friday, April 25, 2003 7:54 AM
To: 'xansys@yahoogroups.com'

Hello All,
Just going to keep this as short as possible. I'm currently doing a very
simple 2D axisymetric model of a standard bolt in tension. Problem is, for
what is a known loading condition which does not produce plasticity or
failure (from years of industry experience), the model is showing massive
stress concentrations around the 'under head' radius. This is, of course, to
be expected, but would classically indicate a potential failure. The Ansys
help people have assured me that the model is correct, and that this type of
anomaly should be expected and not taken literally, but this argument is
quite difficult to take to management! I was wondering if anyone else had
experienced this problem, and if there is an agreed way of determining
failure criteria in this case. By the way, I've only got Ansys 5.5.1, which
doesn't have the failure criteria portion to it.

Thanks for any help

Cheers
Geoff

Geoffrey Cooper
Analytical Engineer
Rolls Royce - Bedford
geoff.cooper@r...
Posts possibly associated with message #49585AuthorDateScore
49576[struct] Bolt Stress ConcentrationsCooper, Geoff geoff.cooper@2003/04/25 
49579Re: [struct] Bolt Stress ConcentrationsMarco Perucchi2003/04/25 
49581Re: [struct] Bolt Stress ConcentrationsMark Krueger2003/04/25 
49585Re: [struct] Bolt Stress ConcentrationsJohn Ceko2003/04/25 
49590Re: [struct] Bolt Stress ConcentrationsRonnie Thomas2003/04/25 
49591Re: [struct] Bolt Stress ConcentrationsChristopher Wright1969/12/31 
49592Re: [struct] Bolt Stress ConcentrationsIan Prentice2003/04/25 
49594Re: [struct] Bolt Stress ConcentrationsPhilippe Vidori2003/04/25