Originally Posted by
Branko D
CF fatigues (like anything does which is light enough that you'd put it on a bicycle), the mechanism is different than for metals.
It will eventually become progressively less stiff, after which it will eventually fail. How long is that eventually depends on how it is made (it is the defects in manufacturing which greatly accelerate the process), how heavy you are, how often you bomb full speed into potholes and speed bumps and so on, but anecdotally, it's about as long as you'd expect a nice metal frame to last before it dies out of fatigue.
Here's some reading;
https://www.academia.edu/30520244/Fa..._Bicycle_Forks
I did not read the references. If carbon fibre lasts on fighter jets, F1 cars, and commercial aircraft over my lifespan, in effect it does not fatigue. The resin? That is a more nuanced discussion. But I have a 30 year old fork hanging in the garage in the sun and it is still holding up.
A bigger issue is probably the extreme light and brittle layups being used where even the bike rack clamp on your car will damage the toptube permanently.