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Eigenvalue and material strength

Eigenvalue and material strength

(OP)
I do a eigenvalue buckling analysis of planar plate modelled with shell elements, I do two runs, one is a static run in which i apply force to my structure by a impactor & save the stress stiffness matrix and exit the, then re-enter with linear buckling analysis. The second run is an eigenvalue buckling run, in which I use the geometry deformed state(last state) from the first run & apply a very small perpendicular force. And i get eigenvalues and modes, eigenvalues are factors by which the applied load would be multiplied to get the eigenvalue buckling load.

My question is i did eigenvalue buckling analysis for 3 cases of steel qste 380, 420, and 460 grade steels, as information only plastic strains and yield point vary in these 3 different steels.
Buckling eigenvalue for steel 380 > 420 > 460 is it possible ? I expected steel 460 is stronger than 380 and required more eigenvalue buckling load to get the first deformation mode, but unfortunately its reversed steel 380 has higher eigenvalue than rest, i am clueless its possible ? please share your views.


RE: Eigenvalue and material strength

2
Linear buckling is only a function of stiffness, not strength.

RE: Eigenvalue and material strength

Well, buckling is only a function of total stiffness, and since the modulus is the same it comes down to geometry, I.
So if the 380 develops less eccentricity (deformation) then it will have less tendency to buckle.
Often with higher strength grades the deformation is more localized and those local areas end up easier to buckle.
The total deformation may be greater in the 380, but it may be spread out more so there is not a local issue.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

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