Learning Forum

[Charlie Rutherford]

Hello,

This is my first time doing FEA in general and my first time using ansys workbench. Im currently trying to determine the effective spring constant of the anti roll bar system for an FS car. However, when i apply a force to the control arm and thus creating torsion on the torsion bar it is exapnding by large amounts and i believe it is to do with my incorrect setup of the software. 

Ive added images showing the issue. I was wondering if it is me setting the software up wrong and if so where or if this is just a design issue which needs to be sorted. Ive tried uploading the files but couldnt find anywhere to upload them however ill upload an image of the all the settings i used.

Thanks in advance for any help :)

 

[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.