What I should do if the critical buckling load doesn't make any sense?

[KyleSong]

Dear friends here:

Thanks for your reply to my previous questions, and I learnt really a lot from this forum, thanks everyone who helped me, May all the things goes well on you!

Now, I found a serious problem when I using buckling in linear perturbation. I know the critical load equals to the load I set in load module multiplied by the corresponding eigenvalue, so I set the load as 1 to avoid further calculation, but after I get the result, I feel surprised at two tings.

Firstly, the eigenvalue is much more bigger than the critical value calculated from Euler critical load formula, I need this value to estimate the load added to the following steps, but now I was totally stuck here...

Secondly, I tried to changed the load value in load module from 1 to 0.1, and hope to see the difference that the eigenvalue for the case has load as 0.1 should be ten times of the case has 1 as load, but to my surprise, the results are just the same! that doesn't make any sense...

Could anyone help me with this issue, I feel really frustrating about this.

Best Regards,
Kyle

 

[Mustaine3]

Try to set the load as close to the expected buckling load as possible.
The buckling load can be off if your structure is imperfection sensitive. Then you have to add the imperfections and do a nonlinear buckling analysis.

 

[KyleSong]

Dear Mustaine3:

Thanks for your kind reply!

Yes, it is a good idea to set the load as close to the estimated value as possible, but since we know the critical load equals to the load I set in load module multiplied by the corresponding eigenvalue, if set it as 1, the critical load could be more straightforward, and this should have happen that whatever I set the load, the value from the load multiplied by its corresponding eigenvalue should be the same. But for my model, it is not, whatever load I set in load module, the eigenvalue never changed, that makes me so frustrated. I need your help Mustaine3!

Best Regards and Sincerely,
Kyle

 

[Mustaine3]

Run a nonlinear step before and set the preload close below the buckling load. Then do the linear buckle step. Maybe your problem is nonlinear before the buckling happens.

 

[TGS4]

Are you doing load control or displacement control?