Eigenvalue Buckling

[m_ridzon]

Folks, I just have a high level question about the ANSYS Mechanical Eigenvalue Buckling solver. It has always been my understanding that the Eigenvalue Buckling solver is a low-fidelity first-pass glimpse of a structure's buckling characteristics. In other words, use of the solver should not be relied upon for final design. Rather, an engineer should run a nonlinear analysis (high-fidelity) with buckling loads to find the bifurcation point for final design considerations. Is that how other folks have viewed the Eigenvalue Buckling solver?

 

[SWComposites]

It highly depends on the type of structure, the loading, the buckling mode, etc. There is no universal answer. Lots of structures have been successfully designed and analyzed using linear eigenvalue buckling methods, with appropriate factors of safety.

Strongly suggest getting and reading Timoshenko, Theory of Elastic Stability.

What is your specific structure that you are analyzing?

 

[m_ridzon]

What is your specific structure that you are analyzing?

I'm currently working on an overhead, underhung crane. But my buckling question was more high level and not specific to a particular structure.

The ANSYS Help Documentation says the following. These statements have always made me pause when I consider using the Eigenvalue Buckling solver for final design decisions.

An Eigenvalue Buckling analysis predicts the theoretical buckling strength of an ideal elastic structure. This method corresponds to the textbook approach to an elastic buckling analysis: for instance, an eigenvalue buckling analysis of a column matches the classical Euler solution. However, imperfections and nonlinearities prevent most real-world structures from achieving their theoretical elastic buckling strength. Therefore, an Eigenvalue Buckling analysis often yields quick but non-conservative results.

A more accurate approach to predicting instability is to perform a nonlinear buckling analysis. This involves a static structural analysis with large deflection effects turned on. A gradually increasing load is applied in this analysis to seek the load level at which your structure becomes unstable.

 

[SWComposites]

Yes, that is a valid warning, but very lacking in details. Some structures, like a cylinder under axial compression (think of standing on a pop can) are very sensitive to imperfections. There are other structural types that are not sensitive to imperfections.
You need to read more than FEA code documentation. You need to understand the fundamentals of engineering mechanics and structural stability.
Nonlinear FE buckling analysis is not a fool proof panacea.