# interpretation of buckling/necking

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Hello at all,

i made an analysis of a wireframe of a formula student car and created some loadcases for buckling.

In HyperView there are some negative and some positive magnitudes for F (for buckling mode 4).

I´m quite sure that this is the factor λ.

So i thought if λ>0  (positiv) there is no buckling and if λ<0 (negativ) then there is buckling.

Now i noticed, in every case where are the negative magnitudes, then a tension rod is buckling or deforming and when there is a positive magnitude then a pressure bar is buckling. I thought only rods/bars under pressure can buckle.

My problem is to interpret these cases.

Could it be that the buckling of a tension rod is a kind of neckling???

And when it is a kind of neckling, how to give an interpretation of the buckling?

Why are tension rods are deforming in my buckling analysis?

I hope you can help me.

Regards,

Rizzo

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Hello,

negative modes mean a change of sign of the loads. If your structure can buckle at this "negativ" loads, then you have of course this modes.

To prevent this (although they are real), put a value of 0.0 or 0.1 to V1 at the EIGRL card. (Optistruct / Nastan)

Best regards,

Mario

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Hi,

As Mario said with V1= blank in EIGRL card, at the value is negative and it signifies buckling tendency at load reversal.

With V1=0 in EIGRL card prevents calculating negative buckling

Thanks to all.

Now it works

Thank you!

Rizzo

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