Buckling Imperfection Factor
Buckling Imperfection Factor
(OP)
Hello!
I'm currently going through buckling analysis, for a hemispheric shell. So it a basically a portion of a sphere.
It is subjected to a pressure load on the external surface, therefore it can buckle.
From handbooks I could calculate the thickness, radius and angle using handcalcs.
But I have to include a knock down factor to account for imperfection.
And the problem begins!!
I don't clearly see the method to do that. I can run a FE model using linear buckling, which will give me a buckling load factor.
Then maybe run a non linear buckling analysis to measure the actual displacement to make sure there is no snap through.
This is the idea I have, it's a bit reproducing a test from where we usually derive the imperfection factor.
But I'm not sure to get it right with this strategy... so if someone knows a good (or better) way of deriving this factor (basically a KDF to be applied to the Young's modulus to account for stiffness reduction).
Thanks a lot for any help you can provide me!
Cheers
I'm currently going through buckling analysis, for a hemispheric shell. So it a basically a portion of a sphere.
It is subjected to a pressure load on the external surface, therefore it can buckle.
From handbooks I could calculate the thickness, radius and angle using handcalcs.
But I have to include a knock down factor to account for imperfection.
And the problem begins!!
I don't clearly see the method to do that. I can run a FE model using linear buckling, which will give me a buckling load factor.
Then maybe run a non linear buckling analysis to measure the actual displacement to make sure there is no snap through.
This is the idea I have, it's a bit reproducing a test from where we usually derive the imperfection factor.
But I'm not sure to get it right with this strategy... so if someone knows a good (or better) way of deriving this factor (basically a KDF to be applied to the Young's modulus to account for stiffness reduction).
Thanks a lot for any help you can provide me!
Cheers






RE: Buckling Imperfection Factor
RE: Buckling Imperfection Factor
What is done in the pressure vessel industry (based on what you have described, this industry might be more relevant) is that a mode SHAPE is derived from the eigenvalue buckling analysis. Then, using the manufacturing tolerances as a displacement scale factor, the "perfect" sphere is perturbed based on the mode shape from the eigenvalue analysis. Then, an elastic-plastic analysis (full true stress-true strain, non-linear geometry, etc) is performed.
RE: Buckling Imperfection Factor
RE: Buckling Imperfection Factor
Thanks for your quick feedback, and the information provided.
TGS4, the structure is a pressure vessel, so I believe it's worth following your strategy.
I'm not aware of the 0.55*Sy as a limit, what is it based on?
So based on the mode shape, How do you perform the non linear analyis?
To run the non linear analysis, my intention was to run a static non linear with a ramp function for the pressure case, rather than a constant load.
Is it the idea you started to develop?
Thanks a lot!!
RE: Buckling Imperfection Factor
RE: Buckling Imperfection Factor