Thin Bodies in Inventor 2013 FEA

[GSE_Dan_A]

Hello all,

I was hoping to get some clarification as to what this warning pertains to (see below)...

I did some reading within AD wiki guide and understand the concept of the 'Find Thin Bodies' action, however; what I do need clarification on is the statement in this warning "One or more bodies which are thing being treated as solids". Does this mean that the bodies that were detected fall under the criteria for being a Midsurface or Offset and that the user has the opportunity to apply these commands in order to make the analysis more accurate?  So if I were to ignore this and continue with my analysis, the members will still be treated as a solid and not as a shell and/or surface (which is what the Midsurface/Offset command produces)?  The members I am using that have triggered this warning are HSS 2x2x0.125 x 12' long. 

Thanks in advance,

[henderh]

Hi Dan,

  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

[janellvincent]

Thanks Hugh,

I just received an error message "degenerate element" becuase I choose to ignore the thin body warnings. I think my model should be considered sheet metal on some portions. I am going to go back and try to fix it now knowing what the problem is. Below is a screen shot of a portion of my monorail model. Any suggestions?

 

[medetitmec_]

Greeting Everyone,

Before you simulate you must find thin bodies to do this , choose contact at here there is automatic button.After that you can immediately pass to the simulation.