Erik Kostson
Ansys Employee

FIrst I would recommend to include an imperfection (noy only via the prestress), so say a half sway (sinus along beam).
What I would recommend is that you run first without prestress and only for 1 mm - just to see that it solves.
(also change the orthotropic - you only need EX, PRXY for isotropic)

If that runs then convergence comes from buckling.

So you would like to use perhaps stabilization (see stabilization command), and/or transient with quasi static option (tintp,quas).

ALso one can start taking away the plasticity to see what effect it has - if it is away and it is still not converging then it is due to the buckling.

Finally I would recommend doing this mechncial not in apdl as it is much easier to troubleshoot.