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PAULKORENKIEWIC1-Visitor
1-Visitor
April 28, 2011
Question

fastener results...

  • April 28, 2011
  • 3 replies
  • 2276 views
I've run an analysis basically consisting of two blocks with internal
pressure, attached to each other with the advanced fastener
functionality with preload. I ran a quick check with 0.000000000001 mpa
pressure to verify and adjust the fastener preload to the desired
magnitude. Then ran the full analysis with the actual pressure (48.3
mpa). Results are odd... or at least I think they look odd. This is a
cross section at the fastener:


I don't understand why I am seeing the block "intersect".... It does
appear that the fastener function defined contact is there, you can see
the stress "ring" in the lower block, but shouldn't that also be there
in the upper block? And shouldn't the contact mean the parts don't
"intersect", or is that just a optical delusion based on the "deformed"
view scaling percentage?

Thanks...

Paul Korenkiewicz
FEV, Inc.
4554 Glenmeade
Auburn Hills, MI., 48326


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3 replies

C
ChrisKaswer16-Pearl
16-Pearl
April 28, 2011
Paul,

It is almost a given that it is an artifact of the deformed scaling
factor. The thing to check is magnitude deflection to make sure the
mating surfaces deform together, very easily seen as having the same
color bands on each mating part. Magnitude deflection should be every
analyst's first result to check to make sure the simulation was set-up
to provide expected results. This will indicate the surfaces are moving
together. Also turn off deformed display, or set it to provide a 1X
scale factor. In addition, you can check contact pressure to make sure
contact has occurred between the clamped surfaces.

Hope this helps,

Chris

Christopher Kaswer, M.Sc.
Principal Engineer
Jacobs Vehicle Systems
22 East Dudley Town Rd
Bloomfield, CT 06002-1002
USA
Chris.Kaswer@JakeBrake.com <">mailto:Chris.Kaswer@JakeBrake.com>
R
randyspeed1-Visitor
1-Visitor
April 28, 2011
Paul,

Before looking elsewhere for solutions to a potentially non-problem,
change the deformed scale to "1". That is the only way that contact
results will look "real".

I like the way you are verifying the preload with minimal pressure
first. We have used the canned fastener functionality quite a bit, and
it is extremely useful. That is - when you need to model fasteners -
which is nortmally not the case.

Randy Speed
www.speedconsulting.com


Quoting "Korenkiewicz, Paul" <->:

> I've run an analysis basically consisting of two blocks with internal
> pressure, attached to each other with the advanced fastener
> functionality with preload. I ran a quick check with 0.000000000001 mpa
> pressure to verify and adjust the fastener preload to the desired
> magnitude. Then ran the full analysis with the actual pressure (48.3
> mpa). Results are odd... or at least I think they look odd. This is a
> cross section at the fastener:
>
>
> I don't understand why I am seeing the block "intersect".... It does
> appear that the fastener function defined contact is there, you can see
> the stress "ring" in the lower block, but shouldn't that also be there
> in the upper block? And shouldn't the contact mean the parts don't
> "intersect", or is that just a optical delusion based on the "deformed"
> view scaling percentage?
>
> Thanks...
>
> Paul Korenkiewicz
> FEV, Inc.
> 4554 Glenmeade
> Auburn Hills, MI., 48326
>
>
I
iapanovitch1-Visitor
1-Visitor
May 9, 2011
Paul,

I agree with Chris Kaswer and Randy Speed that the odd picture is most likely due to the scaling factor, however, still wanted to add my 2 cents.

The matter is that the Fastener feature does not automatically create Contact Interface between the parts, rather, it uses a so called Separation Spring (linear, and very stiff) to enforce the non-penetration condition between the parts, and it does it only over 2 small annular areas (called Separation Areas), concentric to the fastener hole. And it creates Free Interface on the rest of the contacting area.

The point is:
a) The Separation Spring is a very approximate way to enforce non-penetration (but it's a lot cheaper than Contact in terms of runtime), thereforeyou may seesome interpenetration even on those annular "separation" areas
b) and Free Interface fully allows interpenetration beyoned the separation areas

I know it all may sound complicated and confusing, it's just thata moredetailed explanation how the Fastener feature works would takes quite a few pages and pictures. I would probably recommend contacting PTC directly, I know they have a kind of a whitepaper on the subject.

Lastly, you can deactivate this very approximate"Separation Spring" thing by manually creating Contact Interface between the parts, then the interpenetration troubles, if any,should go away.

Hope this helps a bit.

Yuri Apanovitch

(I don't intend to make this all even more confusing, but be aware that most if not all commercially available contact solvers actually allow a tiny bit of interpenetration too).



--- On Thu, 4/28/11, Korenkiewicz, Paul <-> wrote:

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