Mild Steel for wishbone pipes?

[Bharadwaz]

Good afternoon.

I have a question about the type of steel used in wishbone pipe. While the rule book states that the primary structure of the car must be made of steel tubing having a minimum of 0.1% carbon, this part just refers to the tubing used to make the chassis. There is nothing mentioned in the Suspension section either about the properties of steel used to make the wishbone. Does the rule mentioned earlier imply that the steel used to make the wishbones also have 0.1% carbon or is it okay to use steel having less than 0.1% carbon?

Thanks in advance.

[Big Bird]

Hi Bharadwaz,

I cannot give you definitive answers on rules - but there is a system in place through the SAE to officially answer such queries. The following response is more to help you to read rules.
- if a rule states that "component X" must be made of a certain grade of material, then you simply must make that component from the required grade of material. Any rule that is explicitly stated must be followed.
- if there is nothing mentioned about the material requirements for "component Y", then you should be able to manufacture it from whatever material you choose. You don't go following rules that don't exist.
- if there are no rules about the material requirements for "component Y", then the last thing you should be doing is inventing your own rules. You don't go applying the rules for component X to component Y just because you cant find any other rules for Y.
If the rulemakers want you to make your wishbones out of a certain material, then it is their responsibility to explicitly state it. Why would anyone assume that a statement about the chassis' primary structure would apply to an unrelated component in another sub-system? Should we assume that any other components that do not have specified material requirements therefore need to be made of chassis grade steel too? I couldn't find any rules about the specific composition of rubber in the tyres - should I assume we thus need steel tyres? There are no specific rules about what we should eat for lunch - therefore should I assume we must bring along steel sandwiches?

Sorry, not trying to be a smart **se, but sometimes looking for absurd conclusions can help us understand the flaws in our logic.

Now, two questions for you:
1. Before asking this question, did you look for answers? In less time than it would have taken you to write the question, I jumped on google and found any number of FSAE cars that had wishbones of materials other than steel.
2. Is there a rule that states that cars must have wishbones? Might that be another assumption you are making as well?
I look forward to your response.
Cheers,
Geoff
p.s. PLEASE don’t call me sir when you respond – my name will do just fine. Thanks!

[Claude Rouelle]

Tubes, not pipes.

[Michael Royce]

Bharadwaz,
There are no rules covering the materials or design of your suspension wishbones. In fact, there is nothing in the FSAE or FS Rules that requires a team's car to have wishbones!! If you do design a suspension system that uses wishbones, and most teams do, the materials and the design are completely up to the team.

[Pat Clarke]

Bharadwaz,

I think Claude has zeroed in on an issue you have!

'Pipe' is used to transfer fluids or gasses and is usually described by its inside diameter.
'Tube'is used for structural purposes and is usually described by its outside diameter and wall thickness.
As your proposed steel spaceframe chassis is a 'structure' it should be constructed from 'tube'!
Your wishbones, if you intend to use steel, should also be 'tube'.

I don't think you can buy steel tube with a carbon content less than .1%, even humble 1018 steel has .14% minimum carbon content.

'black steel' water pipe may be less, but is totally unsuitable for chassis construction.

Incidentally, this issue has been covered several times on the Supra groups on Facebook.

Pat

[Charles Kaneb]

One characteristic of mild steel is that if you go past the yield strength, it can deflect a long way before cracking or breaking. Normalized 1020 has an elongation at break of 35% - and an elongation at yield of less than 1%. Its ultimate tensile strength is also well above the yield strength, allowing it to yield rather than fracturing when overloaded.

This can save you if you hit a pothole or underestimate the peak load on a wishbone while braking on a banked corner. It can also drive you up the wall when nothing looks wrong, nothing feels wrong, and all of the alignment parameters are somehow nowhere near what you set them to earlier. 2% extension of a 10" (250mm) long A-arm is 0.200" (5mm). That's small enough to not be obvious when you put a tape measure to it, especially if one of the ends is a little inaccessible, and you're measuring between two estimated bolt centerlines! Of course you'll find it, when you measure one that didn't get overloaded and compare, or you get back to the shop and check it off the car, or measure from well-defined clevis edge to well-defined spherical joint holder edge...

You can get alloy steel tube anywhere there are railways, as it is used for field repairs on cars and locomotives. Use it.