Buckling Of Stiffened Composit Panel

I've done very little Finite Element Analysis work, and not all you said is clear but aside from straight out misuse of the software, wrong sequence or whatever, a couple of basic points come to mind.

1. Is the mesh you are using sufficiently fine across the high strength part of the composite and under the point of load application in particular?

2. Without knowing anything about your set up or software, have you made sure that there is a connection (shear connection in particular) between the composite layers.

Of course if the balance of the components in the composite beam/column has to be appropriate. If it is too deep/wide with too large a I value the high strength laminate will buckle away independently, rather than the whole assembly buckle as a unit.

If you post a drawing of the unloaded structure and of the deformation at slight overload it is likely to judge if the reality is imaged well in your program.

I once calculated buckling of beams with nonumiform thickness and as a result all these gave totally wrong results if pure buckling (like Euler) was assumed.

The problem solvers (in 4 of themajor math programs) hopped from the basic buckling mode to higher ones at unknown loads without any indication.

RHABE

I think that Nastran may be correct, especially if the compressive strength of the composite core is low. Highly localized buckling is a common failure mode for composite panels.