Keep the wheels turning. A steel wheel with shell elements has been on my list for a long time. In the past, I always had only aluminum rims with solid elements in the simulation (see wheelstrength.de). In this post I want to focus on the FEM calculation in PrePoMax.
![half steel wheel geometry FEM mesh displacements and stress in PrePoMax](https://fatigue.pro/wp-content/uploads/2023/03/5_half_geo_to_stress-1024x366.png)
I made my own steel design and that is inspired by the wheel of the Sono Sion (sonomotors.com media-gallery). I used an existing printable 3D model from thingiverse.com and derived from that a surface geometry in FreeCAD. And I also punched “fatigue.pro” into the disc with FreeCAD.
![steel wheel geometry in FreeCAD](https://fatigue.pro/wp-content/uploads/2023/03/sion_wheel_v6_FreeCAD-1024x838.png)
I prepared a shell mesh and defined a steel material for disc and rim. The disc mesh group is connected with tie contact to the rim.
![steel wheel with FEM mesh in PrePoMax](https://fatigue.pro/wp-content/uploads/2023/03/sion_wheel_v6_rim_front_mesh_full.png)
I defined a vertical load at the shoulder of the rim over a section of 36 degrees. And fixed the wheel at the five bolt holes in the middle.
![steel wheel load step definition in PrePoMax](https://fatigue.pro/wp-content/uploads/2023/03/sion_wheel_v6_geo_load_step.png)
Now we can submit the calculation with “Run” in Analysis. On my computer it takes lesser than 3 minutes to calculate all six load steps in the CalculiX solver.
Now we can check the results. First of all, always check the deformations.
![steel wheel displacements FEM](https://fatigue.pro/wp-content/uploads/2023/03/sion_wheel_v6_rim_front_disp.png)
Next we can take a look on the stress. Make sure that you are looking at the expanded form of the shell elements (see keyword OUTPUT=3D). Otherwise you will not find the bending stress (compare stress inside and outside in next figure).
![Steel wheel with FEM stress in inside and outside](https://fatigue.pro/wp-content/uploads/2023/03/sion_wheel_v6_stress_in_and_out-1024x468.png)
You can use the “Exploded View” and “Section View” option for a closer look into the contact area between disc and rim.
![steel wheel half with FEM stress animated](https://fatigue.pro/wp-content/uploads/2023/03/wheel_half_stress_outside_animated.png)
If you need more possibilities to plot the results or if you like to use ParaView then the CalculiX result file (*.frd) can be converted into the ParaView VTK format (*.vtu). In the PrePoMax Forum you can find the useful tip “Converting results to ParaView format“.
![steel wheel von Mises stress animated GIF](https://fatigue.pro/wp-content/uploads/2023/03/wheel_v6_PV_ins30d_smallf_animated.gif)
If I am honest, I did not expect such good results and so many possibilities when I use only free available opensource software.
I could also imagine a fatigue calculation in Fatlab or even an additional load case cornering.
Give PrePoMax a try and if you like you can load this example from the steel wheel pmx file (9 MB).