Fork failures

Discuss light weight issues concerning road bikes & parts.
blue151
Posts: 38
Joined: Fri Jun 11, 2010 2:39 am

by blue151

Hi,

I was just wondering whether any has experienced (or known anyone that has) a fork failure that was not due to a crash (including being broken directly in a crash or soon after a crash).

if people have, I would be interested in the age of the fork (approx) as well the material of the fork & steerer and any suspicions on why it may have failed?

The reason I ask is, on my winter bike (8 year old roughly), I have a aluminium steerer that is bonded to carbon fork which I am progressively getting little more worried about fatigue. I have read that aluminium can fatigue leading to failure. I suppose the same can be said about any material.

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Juanmoretime
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by Juanmoretime

Not your exact situation but I had an Alpha Q GS 30 in a raw finish that after 7 years from chips on all the roads I ride I found a hole in the carbon under the crown when I removed my tire to clean and inspect it. Replacing a fork is much less painful than major dental work.
RESIDENT GRUMPY OLD MAN.

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fa63
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Location: Atlanta, GA, US

by fa63

A well engineered fork's fatigue life should be well beyond what a normal cyclist would ride. I wouldn't worry about it.

spud
Posts: 642
Joined: Sat Feb 07, 2009 5:52 am

by spud

carbon doesn't fatigue, though it may delaminate slowly. Aluminum in a steerer is subject to fatigue failure. Personally, I wouldn't risk riding an old aluminum steerer. You can find a cheap replacement fork.

maquisard
Posts: 1861
Joined: Thu May 01, 2008 8:51 pm
Location: France

by maquisard

If a fork fails it is more than likely due to a void in the lay-up during it's construction. The only way to know if this has happened for sure is to do an ultrasound examination of the part. This is the norm in the aviation industry but far too expensive for even the most premium bike parts. Bike designers therefore over build key components like fork steerers and crowns. Special attention is given to the optimising the lay-up process such that voids don't occur.

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fa63
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by fa63

spud wrote:carbon doesn't fatigue, though it may delaminate slowly. Aluminum in a steerer is subject to fatigue failure.


Sure, but I doubt anyone rides a bike long enough to the point of inducing fatigue failure in their aluminum steerer.

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Asteroid
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Joined: Tue Jul 26, 2016 8:43 pm
Location: Los Angeles, California

by Asteroid

A rider went down hard on our large group ride a few weeks back, when his Trek fork snapped at the junction of the steerer and crown.
He got busted up badly, including some of the previously-mentioned dental work. Ugly carnage.
He rode one of Trek's newer models and was not a heavy rider.
The spill happened less than twenty meters in front of me, at about 30km/hr.
Many attended to him (and another downed cyclist), so I did not hang around long.
Let me ask around to see if more details are available.
Oldbie

youngs_modulus
Posts: 512
Joined: Wed Sep 20, 2006 1:03 am
Location: Madison, WI USA

by youngs_modulus

spud wrote:carbon doesn't fatigue


Yes, it does. It's just that fatigue in carbon composites is poorly understood compared to fatigue in metals.

https://link.springer.com/article/10.10 ... 8.77270.1e

spud wrote:though it may delaminate slowly.


See? ;) Yeah, delamination is one failure mode associated with fatigue in carbon composites, especially when there are strong interlaminar shear stresses.

Interestingly, just like aluminum, carbon composites may have no fatigue limit. (The article I linked to above mentions a fatigue limit, but again, fatigue in composites is poorly understood). In orther words, there is no stress so small that it does not add to the part's accumulated fatigue. Steel and titanium both have fatigue limits, so if the stress is small enough, fatigue life is infinite. But a steel or Ti fork with infinite fatigue life would be so heavy that no one on this board would ride it. As fa63 pointed out, a reasonably well-designed part (such as an aluminum steerer) isn't going to fail in fatigue from normal use, no matter what it's made out of.

Asteroid, your anecdote is interesting, but what are you trying to say by telling it? The fact that your friend crashed (horribly!) due to a broken steerer/crown junction, while profoundly unfortunate, doesn't say anything about fatigue in either aluminum or carbon forks. It *could* have been a fatigue failure, or it could have been a manufacturing flaw. He could have overstressed the fork in a previous crash or near-crash (low-cycle fatigue), thus making the fork vulnerable to fatigue from smaller stresses (high-cycle fatigue). All forks are vulnerable to both fatigue failures and manufacturing flaws.

Detailed photos of the fracture area on both parts could hint at a fatigue failure if the break happened in metal. You typically see "shoreline" striations in the break, which shows crack growth, leading up to an irregular portion indicating brittle failure.

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stockae92
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Joined: Fri Sep 25, 2015 5:13 pm

by stockae92

The fork seems to be durable most of the time, even when not being using for its intended purpose to stop a moving car :)

Image

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Hellgate
Posts: 99
Joined: Mon Mar 27, 2017 8:49 pm

by Hellgate

My 14, 15 YO Reynolds Ouzo Pro is working fine. Just don't crash, drop anything on it, or run into anything head on.

Sent from my SAMSUNG-SM-G900A using Tapatalk

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Miller
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Location: Reading, UK

by Miller

blue151 wrote:Hi,
The reason I ask is, on my winter bike (8 year old roughly), I have a aluminium steerer that is bonded to carbon fork which I am progressively getting little more worried about fatigue. I have read that aluminium can fatigue leading to failure. I suppose the same can be said about any material.


Do you have any evidence of degradation in this fork? If not, and this worry is fed by too much internet, my advice would be to stop worrying about this. Unprovoked fork failure is really rare.

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Asteroid
Posts: 216
Joined: Tue Jul 26, 2016 8:43 pm
Location: Los Angeles, California

by Asteroid

Asteroid wrote:A rider went down hard on our large group ride a few weeks back, when his Trek fork snapped at the junction of the steerer and crown.
He got busted up badly, including some of the previously-mentioned dental work. Ugly carnage.
He rode one of Trek's newer models and was not a heavy rider.
The spill happened less than twenty meters in front of me, at about 30km/hr.
Many attended to him (and another downed cyclist), so I did not hang around long.
Let me ask around to see if more details are available.


Following up on my own post.
Yeah, his fork unexpectedly snapped as described.
Full carbon fiber Trek less than two years old. (Model unknown to me.)
Would not surprise those of us among the ride (discussing it) if he pursued a case.
So, yes, even on newer bikes, it can happen. It pays to frequently inspect closely one's equipment.
Oldbie

ntb1001
Posts: 79
Joined: Tue Sep 16, 2014 4:38 pm

by ntb1001

stockae92 wrote:The fork seems to be durable most of the time, even when not being using for its intended purpose to stop a moving car :)

Image
Wow!!!

What a picture!!

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youngs_modulus
Posts: 512
Joined: Wed Sep 20, 2006 1:03 am
Location: Madison, WI USA

by youngs_modulus

You say "full carbon fiber Trek," but it's unclear whether "full carbon fiber" means the frame or the frame and the fork.

I'd love to see a photo of the broken pieces. I'm a mechanical engineer with a lot of experience in composite structures, so I'm not just idly curious.

I have a friend who sustained an ugly brain injury when his Manitou II fork crown suddenly gave way. A design flaw created a stress concentration, which in turn initiated a crack and led to catastrophic failure. That fork, it turns out, had been recalled because of the flaw.

I seriously doubt that there's a design flaw in your friend's fork crown, but there could have been a problem with the manufacturing. In that case, the most likely culprit is a large void in the matrix (assuming the fork is entirely carbon). If so, a photo may show that void or possibly another flaw.

It's also possible that the guy put the bike on the roof of his car and then tapped the top of his garage with the bars (or something like that). I'm not trying to blame the guy you rode with, but all of these things (design flaw, manufacturing defect, user-inflicted damage prior to failure) are possibilities. Pictures would help, but they may also be entirely inconclusive.

To be honest, I think it's a bit early to talk about "pursuing a case" (suing?) without any evidence about the root cause of the failure. The guy might know in the back of his mind that he hit a curb pretty hard two months ago, or he may have clear evidence of a manufacturing defect. None of us here has enough information to say either way. Regardless of that little question, I hope your riding partner heals quickly and is back on a new bike soon.

uraqt
Posts: 816
Joined: Mon Apr 03, 2006 8:53 am

by uraqt

A while back Phil White of Cervelo said that they had fork failures because the way the bikes were handled during shipping. They had to redesign their shipping boxes and in house testing because it.

C

PS it was a video someplace... : )

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