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Inventor FEA

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Message 1 of 4
Billduck
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Inventor FEA

During a simulation, the warning message is "One or more bodies which are thin being treated as solids". It is a 3 1/2 " pipe by 288 " long. The loading is 4 point loads along the length. The fixed points are not at the ends, but inboard from the ends. What does this message mean?

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Message 2 of 4
GSE_Dan_A
in reply to: Billduck


@Anonymous wrote:

During a simulation, the warning message is "One or more bodies which are thin being treated as solids". It is a 3 1/2 " pipe by 288 " long. The loading is 4 point loads along the length. The fixed points are not at the ends, but inboard from the ends. What does this message mean?


Below is a response from Hugh Henderson (ADesk employee who specializes in the FEA world) to a question I asked regarding Thin Bodies within FEA...

 

 

  This is a warning message that is basically saying that the surface area to volume ratio is relatively high for these bodies, and they might be better solved using shell elements.

  If those components are the same ones we looked at earlier this week (square hollow tubing) it may be interesting to use a shell idealization rather than solid elements.  But unless they are very, very long I think solid elements are fine for the analysis.

  However, if you get this message for say very long I-beam geometry, there could be fillets that would cause gaps (missing faces) in the midsurface due to non-uniform wall thickness if the I-beam.  Connectors (bonded contacts to 'bridge' gaps or missing face) are needed to connect the disjoint shell bodies in the midsurface.  In these types of geometry it would be preferable to use solid elements, since the idealized thin model could be too different from reality.  There is also Frame Analysis as a different option, so that beam elements can be used for the long structural memebers.

  In summary,shell elements are best suited for very thin-walled bodies, such as large sheet metal parts or pressure vessel tanks, etc.  One of the main reasons is that (for instance thin plates) you need several layers thick of solid elements in order to not make the meshed model 'too stiff' in bending, and the large number of solid elements needed could make the problem size huge.  With shell elements, this 'too stiff because of not enough layers of elments' is not an issue.  But be aware that with a shell element formulation, we assume a linear stress distribution through the thickness using our DKT shell elements.

Hope this helps! -Hugh

GSE Consultants Inc.
Windsor, ON. Canada
Message 3 of 4
Billduck
in reply to: Billduck

I am not familiar with shell elements. Is that a technique within Inventor FEA? Or are you saying to create the pipe as a solid that has been shelled to hollow it out?

Message 4 of 4
innovatenate
in reply to: Billduck

I've attached a Handout from Autodesk University 2012 about using shells in Inventor Stress Analysis. I believe this may answer your question. Let me know if you still have questions after reviewing the handout. 

 

Thanks,

 

 

 




Nathan Chandler
Principal Specialist

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