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please help for postbuckling analysis in ANSYS

I am trying to perform postbuckling analysis of plates in ANSYS. But something confuses my mind. After linear buckling analysis I use scaled firtst buckling mode shape to generate initial imperfections. Then I initiate nonlinear geometric analysis by NLGEOM command. Collapse load or final converged iteration changes according to NSUBST option. I am trying to give higher Substep to obtain more sensitive and reliable results like 10000. But NSUBST with 100 sometimes reaches higher loads than using 10000. Which one is a correct approach?

Could anyone help me?

Thanks alot....................

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Jayadeep U. B.'s picture

Hi,

I am not an expert, but I will just add two points, which appears relevant to me.

1. A more accurate analysis should predict lower buckling loads, and hence I don't see anything confusing in your observations.  However, the exact load, which you are going to consider as the buckling load, may need some serious considerations, as the non-linear analysis is going to give you a continuous curve.

2. If you need to perform post-buckling analysis, I believe that you will have to perform a displacement controlled analysis.  I don't think, even arc-length controls are going to give you convergence beyond the buckling load in a load controlled analysis.  Isn't it possible to get the buckling load from reaction solutions in case of displacement control?

Hope the above points are useful. Regards,

Jayadeep U.B.

First thanks for your interest

I investigated displacement controlled analysis for postbuckling after your suggests. Some research papers and ANSYS help menu mention about that. But they are not clear and I could not conceive how to adopt my APDL code. So could you give a basic APDL code for displacement controlled postbuckling analysis.

Best regards.

Talha Ekmekyapar

Jayadeep U. B.'s picture

Dear Talha,

I am not working extensively in ANSYS nowadays, and I do not have any APDL codes.  To be frank, I have never done a postbuckling analysis, and hence I am not even competent to write one... The above comment was just based on my conceptual understanding of the problem.

Regards,

Jayadeep 

I did post-buckling for beams and plates. But for  cylindrical shells there is a problem.  The first buckled mode after the nonlinear solution completed is different from

the linear buckling mode. In nonlinear modes there is no crests and trough ( m and n loops). How to tackle this problem. Can anybody  resolve this using ansys APDL.??

 Jagadish

 

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