Linear Buckling with Prestress

[darrenlovesmusic]

Hi,

How can I perform a linear buckling eigenvalue solution with a prestressed model? (Nastran In_CAD 2018) The pre-stress is 14 psi (external) with a second load of 10 psi. 

Thank you. 

@John_Holtz Is there documentation for STATSUB case control for the 2018 version? 

[g.ceruti · Accepted solution]

Hi @darrenlovesmusic ,

I think you have to perform two buckling analysis, because Nastran Incad manages only one loadcase at time.

However,  linear buckling analysis provides eigenvalues which are load multiplyer, so if:

• conatraints do not change form Step1 to Step 2
• pressure loads are applied on the same surfaces in both Steps

the eigenvalues of Step 1 results 1.4 times (14/10 psi) those of Step 2 analysis 

[darrenlovesmusic]

@g.ceruti , is it possible to superimpose an known eigenvalue displacement from a linear buckling analysis onto a nonlinear buckling analysis? 

[g.ceruti]

I think there is a method to export the displacement result into a text file, than you have to edit the nastran input file to use it as new node position (but then you have to perform the analysis outside the Inventor Nastran ambient)
Try to read this:

https://forums.autodesk.com/t5/inventor-nastran-forum/nonlinear-buckling-imperfection-from-linear-bu...

I'm not sure, (so you have to verify, or maybe someone can confirm or not) a nonlinear buckling analysis performs a linear buckling analysis using the model updated stiffness resulting from the nonlinear static subcase, and not the initial indeformed model stiffness as a simple linear buckling analysis does.

[darrenlovesmusic]

@g.ceruti  Yes, I read the question, but I guess its very complicated. Meanwhile, Inventor will take only one subcase for buckling, which is a true bottleneck. I hope this might be something to consider for future releases.