Skin Panels Buckling 1

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Hello all.
Well, I am looking for some advice about how can I obtain the loss of rigidity in a curved panel when there is a hole in the middle of it (from buckling point of view). I've made two run in PATRAN/NASTRAN considering an intact panel model and another one with one hole. Is it the eigenvalues relation (SOL105) the loss of rigidity? The thing is that I don't know how to include the post-buckling effect in the models. Probably, the post-buckling effects smooth the hole presence.

Beside, how can I calculate microstrains in the hole's borders?
Thank you all. Best wishes.

 

[plasgears]

The post buckling model should have the buckled section deleted, and the stiffeners should have the contribution of attached effective skin thickness as described by Bruhn.

 

[SWComposites]

To predict post-buckling with a FEM you need to run a non-linear large displacment model with an initial displacement imperfection generated from the eigenvector from the buckling solution. Consult your FEM users manual or other posts in the Finite Element modeling forum on how to do this. The "loss of rigidity" is a funtion of the amount of post-buckling load. Strains can be obtained from the FE results for the elements at the edge of the hole; just be sure the elements are small enough to give an accurate prediction given the stress/strain gradient at the free edge.