Simulate Early, Simulate Often... In Rhino
Simulating Pin Connections
I'm working on a lifting rig under very high loads. I'm trying to simulate the pin connections at the links for each part of the frame. As I understand it, SnS does not do linkages just yet so I'm trying to tackle this in a peice by peice fashion. I appear to be getting results that are well higher than what simple hand calculations would suggest. Anybody have any good advise about how to properly load holes to reduce artificial stressed caused by "puckering".
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Link.3dm, 3.2 MB
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Replies to This Discussion
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Permalink Reply by Bob Johansson on
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HI:
I love this question.
The pin load is represented by a sinusoidal
pressure distribution.
The loading force is distributed along the edge of the
hole in a shape represented by a sine series. In a sine
distribution for the normal load, carried over by an absolutely
rigid pin into a plate, was recommended for both isotropic
and anisotropic materials. It was shown that two
other distributions, significantly different from the sine distribution,
did not result in significant changes of the calculated
stress field for one configuration considered.
If the load distribution around the hole is expressed by
4psinh/p then the loading force F resulting
from this symmetrical distribution of load related to the
axis y is of magnitude 2pRt, where p is the bearing stress
according to the classical definition, R is the radius of the
hole and is the unit thickness of the plate.
Bet you didnt expect an answer.
bob
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Pin Loading.jpg, 11 KB
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Permalink Reply by Michael Freytag on
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Rob,
I assume you are restraining the contact patch of one bore and applying a load to the contact patch in the other. What happens in this scenario is that there is a non-physical stress concentration near the edge of the restrained patch. Mathematically, the restraint is infinitely stiff. In reality, there is deformation of both the bore and the pin giving a distribution more in line with what Bob posted.
The closest approximation I can suggest with what is currently available in Scan&Solve is to apply equal and opposite vector forces to the contact patches of each bore. Then, for numerical stability, restrain the model somewhere else. In the example below, I've "drilled" a small hole through the center of the part. I then restrained the straight seam edge in the hole:
You also will want to increase the resolution to improve the accuracy and smoothness of the results.
Does this help?
~Michael
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Permalink Reply by Rob Zavatsky on
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Yes this makes sense now. Would there be any noticeable benefit to further dividing the load patch and applying an approximate sinusoidal distribution? I guess this is also one for the wish list, that is, uneven load distribution capability.
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Rob,
Off hand, I don't know what effect that would have on the stress distribution. You could try it pretty easily, but be careful to balance the forces if you do the restraint as I proposed.
~Michael
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Hi:
If you wanted to email me the lug I could put a pin into itand run
it in ANSYS using both a fictionless and rough contact. We could then compare
the results. Send me a message if you wanted to give this a try.
Thx,\
Bob
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Bob,
Thanks, the model is posted to this forum in .3dm V5. Have at it.
-Rob
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I retreived that lug , What magnitude of load are you
putting on it?
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The lung needs to hold 224000 lb
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I design stuff like that for the oil industry all the time.
Being legally liable is a bit stressfull at times.
Bob
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That's why I've gone throught the hand calcs to verify the results.
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Rule of thumb:
The center ofthe hole should be located no closer
than two diameters from the edge of the plate.
Is that right?
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