If you have attempted to work in Inventor Nastran with an Inventor model that was created using content centre I-beams and the like, you might have thought, great I can convert those components to midsurfaces and then generate the analysis, run the simulation everything will be perfect.

While this is the general practise of creating bodies that very long body vs thickness, when working in FEA with Nastran you will come up with some problems.  The first is the issue where Nastran will break your model.  The surfaces that get created in Nastran do not hold their connection to the Inventor model for very long.  It might be after you run one simulation, it might be after the tenth simulation.  You can never tell but what I can guarantee is that it ill break.  So what can we do about this.

RECREATE the model.

I cannot put enough emphasis on the fact that a CAD model is NOT an FEA model.  If you are going to be using a model with numerous thin bodies, then create the model from scratch with surfaces in Inventor.  This will save you an enormous amount of time when trying to adjust the model to get better results once an analysis/simulation has been completed and you see see there is room for improvement.  It will also save you from having a nervous break down when you open your Nastran environment and all the surfaces have moved away from the CAD model position which means that you have to then delete the Nastran surfaces that have been created and start over again.  Also there is no guarantee that you will complete the recreating of surfaces as the model might break at any time.

This is a known issue/problem with Nastran.  If you would like to learn more, this is a thread from Autodesk Knowledge Network.

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