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cosmoswork buckling analysis result does not match hand calculation

cosmoswork buckling analysis result does not match hand calculation

cosmoswork buckling analysis result does not match hand calculation

(OP)
I am trying to do a simple buckling analysis of a delrin pressure case using cosmoswork.

Case dimension:
OD: 8"
wall thickness: .4"
End cap thickness: .4"
Length: 2.625"

Material properties:

E: 2.83E+9 Pa
Yield stress: 8.9e+6 Pa
Poisson ratio: .3

Test load: 14.7 Psi

According to Roarks's Formulas the end cap should fail approx around 10m.

But the program give a load factor of 54 and the center of the end cap bulge outward rather than inward.

I am wondering wether I setup the analysis correctly?  Any help or advice would be greatly appreciated.

Thanks

RE: cosmoswork buckling analysis result does not match hand calculation

Hi Donaldlo,

I did a very quick run and go the same answer 54.  Sounds good, right?  

No. The problem is that you appear to be using the CW "linearized buckling analysis" that uses a linear analysis engine that does not account for the membrane stress created due to deflection.  I believe this membrane stress is significant in this analysis so you should not be using this method.

Regards,

ERT
http://www.akeng.com

RE: cosmoswork buckling analysis result does not match hand calculation

I would doubt if Roark's formula involved any non-linear effects but probably assumes much more than an FE analysis and is probably more 'incorrect'. Can you give the case number used in Roark?

corus

RE: cosmoswork buckling analysis result does not match hand calculation

(OP)
Thanks for your response ERT and Corus.  In terms of Roark's formula I used case 1c for the cylinder and case 10a for the end cap.

Thank again.

Donald

RE: cosmoswork buckling analysis result does not match hand calculation

Donald,

We must have different versions of Roark as our case numbers do not line up.

I think that you should focus on the end cap. Can you find a case that has edge compression and lateral pressure? I cannot.

Sounds like a physical test maybe a better approach.

Regards,

ERT

RE: cosmoswork buckling analysis result does not match hand calculation

I'm not sure which cases you're referring to either. In my version of Roark VI ed. I'd use case 20 of table 35 for the elastic stability of a thin tube with closed ends (if that's what best describes your pressrue case)

corus

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