genejockey 

I don't know about that, but I did see on Top Gear some time back (of The Grand Tour), where Richard Hammond's CF-bodied Ferrari suffered considerable... erosion from being driven at high speed on unswept tarmac covered in loose stones.

Bob Ross

...until you collide with a micrometeor travelling at any speed in any other direction.

GhostRider62

I miss that show. Thanks to the woke morons, it is gone.

I've only had one serious failure, it was aluminum. I was hurt. Bad. Very bad. I've ridden carbon frames since December of 1985. I can only say it does not scare me.

tomato coupe

What does getting hit by a meteor have to do with the longevity of carbon fiber?

genejockey 

Ask the dinosaurs.

Bob Ross

Apparently this thread has just become a statistic in the Two Decades Of Progress In Math And Reading thread.

tomato coupe

???

bampilot06

Not accurate.

Part 91 aircraft used for hire require a 100 hour inspection. Example: cessna 172 used for flight instruction. I can assure you that the mechanic is not checking for micro cracks on every square inch of the airframe.

Airlines go by cycles. Every part has to be inspected at a certain amount of cycles, and each part has a different cycle requirement, and it varies for each airframe.

Branko D

Well, from what I read, CF bits will become progressively more flexible before they are at risk of, essentially, fatigue failure.

Which is good news, it won't just "fail riding along".
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Trakhak

Where did you read that? Haven't come across that sort of claim for many years, and never about carbon fiber. Perhaps it's an updating of the bike racer folk wisdom that steel frames become softer with accumulated mileage. (They don't.)

Shadco 

What should I replace my 18 year old cf fork with?

.

datlas 

If it's undamaged, keep it. If you think it's damaged, get a new CF fork.

PeteHski

I suppose theoretically CF parts could become more flexible as the resin ages, but in practice I don't believe there is much evidence to suggest that they actually do. So I really wouldn't worry about this particular aspect of CF.
IME of using CF in motorsport, any failure is far more likely to be due to impact damage, inappropriate loading or some kind of design/production issue.

Branko D

​​​​​
https://www.academia.edu/30520244/Fa..._Bicycle_Forks

https://www.ncbi.nlm.nih.gov/pmc/art...9/#!po=24.5763

And so on and on.




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Koyote

From the abstract of the first paper you cited: "This paper presents the results of fatigue and impact testing on bicycle forks that are known to have quality-related manufacturing defects."

So, they started with cf forks that were defective, and measured their responses to stress cycles. Does not seem relevant.

The second paper is not about bike forks specifically and includes much terminology that is unfamiliar to me -- so I don't know whether it's relevant.

himespau 

More importantly, have the baby bolts showed up yet? Are they still missing?

Branko D

Well, some forks in the first paper lasted for a lot of cycles and some didn't, depending on the kind of manufacturing defect (which, you know, are present on most forks, it's just a question of how many and how significant, and they hugely impact fatigue life), which all exhibited a gradual loss of stiffness before fatigue failure, as you would expect.

The other is just about generic fatigue modelling of composites. The earliest reference on residual stiffness dates from 1975. It is not exactly news. You can read a heap of the stuff if you like.



Before metal lovers latch on, I've just recently read a paper about fatigue modelling and testing on a steel bicycle frame and it of course died to fatigue, and depending on pedalling forces and their angle, in significantly less cycles than a quality made CF fork would.

If you ride lots and lots of miles for many years, one day you will have to replace your bike. I wouldn't have thought that this would be so controversial.

datlas 

Stollen

Sadly, the original Baby Bike Bolts thread is locked so you have to look for it.

genejockey 

Solution: multiple bikes, so each one accumulates wear more slowly. And my wife thinks I'm crazy to have 10 bikes.

Symox

You may be shocked at how strong the thing is. I did this to a fork after an accident. Banging with a sledgehammer left only a scratch. Trying to compress the legs in a vice (got scary after reducing span by 1/2 with no cracking sounds - released and was fine). Cut with a hacksaw and even with a 1/3 cross section cut I couldn’t beak it apart by bending on my knee. I believe carbon forks are ridiculously strong (at least those that pass testing requirements). I have no worries about a carbon fork disintegrating or weakening over time from normal use. With normal use it should last a lifetime or three

Branko D

N+1 is always the right answer

Koyote

In the middle of the pandemic, as we were driving home one day, I was telling my wife about the bike supply chain problems. As we pulled into the garage, I waved a hand at my five bikes, and said, "I'm pretty smart to have stocked up, aren't I?" Her agreement was a bit less than wholehearted.

himespau 

Man, it's been a while since I've had some good stollen.

Bacciagalupe

I don't see these as comparable. Helmets aren't load-bearing items; are intentionally designed to be replaced; and aren't made with carbon fiber Helmets are consumables, forks are durables.

If a bike manufacturer told you that you had to replace their frame every 5 years, do you think those frames would sell well...?

datlas 

I was trying to find a rational reason why a company would say replace the fork every 5 years and ongoing sales is the only reason I can think of.

The helmet analogy is not perfect, and belongs in a different thread, but clearly a helmet that has been cared for and not crashed does not need to be replaced either.