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Linear and non-linear buckling

ramdas chennamsetti's picture

Hi all,

When we do a non-linear buckling analysis, initially we introduce some imperfections (mode shapes of mode 1, 2 etc) from eigen buckling analysis. Then we multiply the load with eigenvalue of the first mode. This load is applied on the structure having imperfections. Now put on non-linear geometric option and run the analysis. At bifurcation point we get non-linear buckling load. Non-linear buckling load comes close to eigen buckling value.

Decription of my problem is as follows. 

I have a big structure say 10 m length, 3 m width and 0.02 m (=20 mm ) thick. It is subjected to a complicated loading and constriants. When I do a linear buckling analysis, local buckling is taking place (mode shape is confined to an area of 1m X 0.2 m). Buckling factor is 1.3. I used the corresponding mode shape to introduce imperfection, mutiplied load by 1.3 and then arryied out non-linear buckling analysis. The load factor computed is 2.3. The whole structure (globally) is undergoing deformation.

My questions/statements are as follows.

1. When a local buckling takes place in a structure, the load factor obtained in non-linear buckling analysis is not in the close to the load factor obtained in linear buckling analysis. Correct or not?

2. If the above statement is not correct, what could be the probable mistake that I am commiting in carrying out non-linear buckling analysis?

3. What checks shall I carry out?

I request to give a thought on these issues.

Thanks in advance and regards.

- Ramadas


ramdas chennamsetti's picture

Hi all,

I have fixed this problem. Thank you all!!!


- Ramadas

I need help on imperfection buckling analysis please help me



I read your various blogs and comments  andgot an idea that you have a good grip on Ansys. Sir I am a BE aerospace student,and I am doing my final semester project on FSI,flutter analysis of wing,I have read S.S Rao's Mechanical Vibration book,so I have developed understanding of vibration,natural frequencies etc but sir I dont know how to start the project on ansys,wheteher to use ansys and cfx or ansys and fluent,what benifits will I get in each case. Can you please help me by just providing a starting point. 



Muhammad Amir

I am performing a nonlinear buckling analysis on two shells.symmetric contact is established between two shells. Hydro static pressure is being applied on the outer shell.The issue is the gap between two shells is 4mm but even after applying pressure even upto 200MPA .I cant see the contact between them and the max deflection goes upto 5 mm but i cant see the contact?



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