Part critique please

[Dimman]

Originally Posted by EarlQHan

ZDan - Motorsports doesn't have structural engineers per se. It's tasked to the individual design engineers to carry out the process from cradle to grave. I agree with your logic wholeheartedly though.

Without breaking confidentiality, I can say the arm was developed to withstand the following loads:

10G instantaneous bump
1G braking + 2G cornering + 1G bump combined
2.5G cornering

Weight transfer effects were considered.

Are there more efficient designs? Yes. Are there more effective materials? Yes. But there were other aspects they had to consider.

Stance is a value brand that offers good quality at a good price. If I had to compare suspension brands to stores, with Megan Racing being the dollar store and Ohlins being Whole Foods, Stance is like Target. You get everything want and need without breaking the bank.

How much thought was put into fatigue? Flipping through one of my Carrol Smith books (I'm only a do-what-I'm-told machinist...), I get the impression that he would not be happy with the layout of the holes (for adjustment, or to use one part for multiple applications?) from a stress riser point of view. Especially given they are aluminum, right? I think Mr Smith wouldn't have the not-used holes, as well as having a 'boss' on the one that is used.

Also, why the sharp radius on the machined bend/kink? CNC could have cut a large radius 'banana' shape just as fast.

They also don't 'look' like they would handle twisting loads well, either.

Finally, you mentioned stiffness increases with aluminum based on shape before. If there is no major increase in height/width, and aluminum is ~1/3rd as stiff as steel, is there a chance that stiffness is actually less than original? I'm just thinking about hollow anti-roll bars being almost as stiff as solid because the central cross section material doesn't contribute as much.

@ZDan thoughts, too?

[ZDan]

Originally Posted by EarlQHan

ZDan - Motorsports doesn't have structural engineers per se. It's tasked to the individual design engineers to carry out the process from cradle to grave.

Then the design engineers *are* the structural engineers. Doesn't mean they aren't up to it, but for primary structure on a race or road vehicle, IMO you *must* have qualified structural engineers in on the design. Anything less is unethical, immoral.

These are parts that, if there is a failure, human injury is a possibility. I.e., FMEA severity ranking is 10.

Without breaking confidentiality, I can say the arm was developed to withstand the following loads:
10G instantaneous bump

Is that a dynamic/transient load, or just 10x static load?

1G braking + 2G cornering + 1G bump combined
2.5G cornering

These types of loads generated by tire grip are relatively benign relative to road hazard/impact type loads.

It's worth noting that, in racing, parts can be *heavier* vs. standard parts, to be able to withstand hard impacts and continue.

Weight transfer effects were considered.

I hope so!

Dimman correctly brings up fatigue. This is a huge concern as the parts are aluminum, which has no fatigue limit (i.e., cracks *will* eventually occur, even if the design is for very low stress levels).

Are there more efficient designs? Yes. Are there more effective materials? Yes. But there were other aspects they had to consider.
Stance is a value brand that offers good quality at a good price..

If I worked for them, as structural engineer, my approach would be to design for higher yield and ultimate strengths vs the OEM part under similar load cases to those above, and to ensure that stresses remain below yield at ~5x static load to prevent high-cycle fatigue.
And then conduct static and fatigue testing to validate parts before selling them.

[OICU812]

Lots of time has went by haven't read of any failures or issues with these?