Torsion problem on a flat sheet

[Jonny Flowers]

I have a flat sheet that I am applying a torsion to at 2 ends. However the issue I seem to be having is that the rotational displacement seems to only go a couple of degrees and stop. I have my base fixed using ENCASTRE and the top is related to a reference point that I can apply a rational displacement of 1 rad or 10 rad and it still turns the same amount. Any ideas?

 

[Mustaine3]

- Is the analysis nonlinear with NLGEOM?
- Deformation scale factor set to 1 in postprocessing?