The FEA study is based on the tubing being 45mmOD with a wall thickness of 2.6mm and produced from cold drawn steel. To keep the post short I have decided to take out all the maths and boring parts and leave you with the pictures as results
The first test based on the stress of the material and for simplicity of this initial study I decided that I would base the test on 60mph to 0mph instantly with a mass of 60Kg this will be throughout for the images loaded here unless otherwise stated and I end up with a full report which I don't want to do currently.
The image you see here is with the above figures but the image depicts a scale of 225 times the actual displacement so to show the CAD user where the faults lay (easier to see)
As you can see from the above picture the load is across the harness bar facing in the direction of pull and is also fixed at the base shown in green.
If I turn off the scale you will see the actual deformation / displacement
Also I believe it is good to see where the maximum displacement is so this scale 1:1 shows where the movement of the cage is greatest, which for something as simple as the cage shouldn't be hard to work out.
The Displacement shown in red is 7.45mm under maximum load
As a simple conclusion to my workings and CAD data I am sure that should the worst happen and I end up in a high speed crash the cage will support me, just a question of the rest of the car...
Assume a peak acceleration of 50g (more than that and you are going to have a bunch of other problems) gives you a force of 30kN, you'll probably take about half that through the shoulder harness.
ReplyDeleteBut that is not the primary loadcase - try a federal roll over test as a starter, look up fmvss 216. FIA also use this, plus a vertical load on the main hoop of 7 * GVW+150kg.
T45 tube will yield around 620MPa and you'll need an explicit FEA solver to accurately model the failure mechanism.