i'm modeling a plate in abaqus under cyclic loading and i faced with "negative eigen value" error that occurs because of buckling of plate in opposite side.
Dear Mehdi,
What is the step you are using? The negative eigenvalue in context of buckling basically means the structure may buckle if the load direction is reversed. However, in analysis this usually shows up as a warning and is not a cause of termination of analysis. Other conditions that can generate this symptom and can cause simulation failure are usually related to poorly defined boundary conditions or sometimes material inputs.
Dear friend
first of all excuse me for delay, yes i'm modeling a plate under cyclic loading and in compression part of loading this error presents . i'm using general static as my step of analysis . if u have an idea for modeling buckling please let me know, tnx
With the new information, I think the negative eigenvalues in your analysis means the model becomes unstable. Specially that you say it occurs in the compression part of the cycle. To solve this you have to change the step.
To study buckling, the step needs to be linear perturbation, *buckle. Static or other steps can precede it,to apply pre-loads/displacements (the parameters that are not directly causing the structure to buckle). Afterwards, another step for the actual buckling analysis (presuming a linear or eigenvalue buckling analysis is intended) should follow with *buckle. If you do not want to consider pre-loads etc. and the only load you have is the one that is causing buckling, then just use a *buckle analysis. From there you get the critical force for the modes of buckling.
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