Reply To: Issue with material expanding when in torsion

[peteroznewman]

Hello Charlie,

The expansion of the diameter when the part rotates is a natural consequence of the small angle assumption all FEA programs make to do a linear analysis.  I found a good explanation on Autodesk Nastran support and that is exactly what is happening in your model.

I assume that the control arm actually rotates by a significant angle and the deformation display scale factor is set to 1.0 (True Scale).  The other way to get a visual expansion effect with a small angle of real rotation is to set the deformation display scale factor to a huge number. Then the expansion is just a graphics artifact and is not real.

The corrective action is to remove the small angle assumption. Under the Analysis Settings set Large Deflection to On. That will change the linear analysis into a nonlinear analysis and the solve time will increase, which is why the default setting is to leave Large Deflection set to Off, since the small angle assumption is valid for many models and those don’t need to spend any extra time doing unnecessary computation.