Hello everyone!

I'm trying to solve a beam bending problem with large deformations and preloaded state.

Model problem:

A beam, 1 meter long, of circular cross section is terminated at both ends, the load is applied at the middle of the beam.

The first step is to apply the load and unload the deformed state (inistate)

The second step is to change the geometry (upgeom) and load the deformed state.

The solutions in the first and second step should be identical.

Result:

The solutions in the first and second steps diverge significantly for small loads.

As the loads increase, the solutions begin to converge.

What's scary is the error (last picture) in the results on the second step - as if the file with the results of step 1 is being read incorrectly.

However, when nlgeom and upgeom are disabled, the solutions converge.

At the same time, when zero displacements along the X-axis (in the load direction) are disabled, the solutions converge in any case.

Can you tell me what the problem is?

And how can this problem be solved?

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Macro downloaded in the attachment.