Imperfection Analysis

[burningliquid]

Dear All,

I am currently designing a monolithic spherical vessel under uniform compressive pressure and would like to investigate how deviations from the “ideal” spherical shell shape (e.g. non-uniform thickness) will affect its critical buckling load.
Any suggestions on approach this problem would be greatly appreciated.

Kind regards
burningliquid

 

[gwolf2]

Do it using FE, almost any will do. Use solid HEX8 elements and nonlinear stress/strain material curves. Apply a really big pressure load around 3x estimated failure, set the analysis to automatic load incrementation. Run.

The analysis will cut back with successively smaller load increments very near the buckling load until it eventually halts for a number of reasons. Your critical buckling load is within a few percent of the %load that it got to.

gwolf

 

[bassmanjax]

I would use shell elements - much easier to tweak the wall thickness if required.

Then, run an eigenvalue (linear) analysis to get the buckling loads and mode shapes. You can then examine the mode shapes, and use these in an imperfection analysis.

There is a really good example in the ABAQUS docs;
"1.2.6 Buckling of an imperfection-sensitive cylindrical shell".

Regards

Martin Stokes CEng MIMechE