Hi Armin,

The eigenvalue analysis is based on the elastic assumption for the material. If the cylinder is thin-walled and fails due to elastic buckling, then the eigenvalue should be the value you are looking for. If the developing stresses are in the plastic zone and the cylinder fails by plastic deformation, then your prediction is not accurate. You should also account for the effects of geometrical imperfections and residual stresses (if present in your problem), which are highly affecting your results. The simplest thing to do is to run FEA with elastic-plastic material properties.In terms of equation, check the Rankine's buckling formula.

Regards,

George

Thank you George