Obviously, you have to take into consideration the entire design, not just the material.
If you are suggesting that aluminium can never be used because of fatigue, then perhaps you are unaware of it’s use in aircraft manufacturing, or perhaps more relevant to this discussion, in aftermarket drive shafts for performance cars.
A lot of our esk8 stuff is not easy to engineer on paper. I’d argue half of the battle is experience or just general know-how. There is so many forces, moments, vibrations, temperature effects that as @b264 said, your best bet is to just over-engineer the damn thing.
Sure it seems inelegant and brute force for the discipline that is design, but it gets the job done. The best way to see if stuff works around here is to test it, and test it hard.
I guess one approach we can take is to run the numbers, but have a huge safety factory of 3 or higher. Aircraft have a safety factor or 1.2-3.0 because saving weight has a huge economical advantage. For esk8, I am not convinced that reducing weight is as critical. Weight for esk8 only matters when you gotta pick up the damn thing, which happens less when it isn’t broken lol.
My point is esk8 parts have so many uncertainties in their service that its a poor idea to rely on numbers alone. People break everything around here no matter what your math tells you 
Kevin just dropped the mic
We were talking about different things.
Sorry, took me a while to get back to you. Was shuffeling my way through all these aluminum bicycle frames that failed due to fatigue.
Let it go…
hmm…
“Aircraft lifespan is established by the manufacturer,” explains the Federal Aviation Administration’s John Petrakis, “and is usually based on takeoff and landing cycles. The fuselage is most susceptible to fatigue, but the wings are too, especially on short hauls where an aircraft goes through pressurization cycles every day.” Aircraft used on longer flights experience fewer pressurization cycles, and can last more than 20 years. “There are 747s out there that are 25 or 30 years old,” says Petrakis."
source: https://aviation.stackexchange.com/questions/37826/what-is-the-fatigue-life-of-a-fuselage-based-on
You clearly don’t want to understand, or it’s just the huge ego.
Everything fails.
But you can still make it work for you (not you specifically, people who talk less and do more)
I’m out.
@professor_shartsis seek life elsewhere.
Exactly, we simply don’t have data of the loadings, and adding a few grams is nothing
If anyone have a few thousand dollars of high performance accelerometers laying around let us know 
And more, I say the 3 safety factor if you are using aluminum and just a static loading are way too low
Make it have a overall high safety under easily determined loading and go all out to minimize any stress concentrations, that’s where your parts will start to fail
I can’t go into specifics, but the Hypertrucks for example have way way more than 3
You do know that as the stress reduces linearly (fatigue strength), the no.of fatigue cycles before failure will increase exponentially right…? An endurance limit doesn’t mean much when it needs 10^10 cycles to fail…
Pretty much this. If you board lasts for 20 years, is fatigue really an issue? I’d bet other parts on the board will fail long before fatigue failure occurs.
While this could be fatigue failure, it seems like the origin came from a stress concentration on the left on the axle (potentially a void/ initial crack). This may just as well be an isolated case… You seem to have studied/read about fracture mechanics before, as such, I’m sure you know how a single stress concentration can lead to many different modes of failure.
Static loading doesn’t mean much. It’s simple math.
Shock loading is where this conversation should be. A hanger bending is always better solution than breaking. All parts have a usable life. The important question of any part is how does it fail and how much time is its usable service. With any mechanical or stress induced part, there is always a trade off between performance and durability. Math is precision. Keep in mind most functions are created from a world of approximates. Finding the failure point by stress testing the part is the only way to know what you have.
I found this calculator for torsion of solid and hollow shafts:
https://www.amesweb.info/Torsion/TorsionalStressCalculator.aspx
Could you just fucking not, for like, a day?
Stop complaining and charge your phone.
Nothing that comes from my keyboard is serious. You do realise this by now I hope.
Well sometimes but its pretty rare. 
Free hugs for everyone!
