steerer tube fatigue and fatality

Discuss light weight issues concerning road bikes & parts.
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mrgray
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by mrgray

hi
found this article today in sydney paper.

http://www.smh.com.au/business/consumer ... ss41s.html

refers to weight weenie parts and the ability of these to hold up to use over time. raises the idea that expiry dates might be put on specific parts. part in question was aluminium. do we have fatigue issues with carbon? or is aluminium particulary prone to this?
Bobo S&S Steel Bike - 7.5 kg
Oltre XR2- 6.6 kg
Look 585 - 6.8 kg

by Weenie


beanbiken
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by beanbiken

yes an interesting read and a tragedy as well.... Don't know what the answer to this one is
Ahhh, coffee & carbon

RussellS
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by RussellS

"The coroner determined the crack... and deemed it an "inclusion flaw" from the manufacturing process."

I took this from the article. Inclusion flaw from the manufacturing process would indicate the part was built with an inherent flaw. So the fork could have broken in the first mile or the 10,000th mile, as happened here more or less. But after 10-20-30 thousand miles of use, it would be awfully hard to argue the part was built with a flaw built in when manufactured. The fork broke. Almost everything will break sometime, somehow. I'm sure we could find a broken anvil if we looked hard enough. Unfortunately in this case the guy died.

pdlpsher1
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by pdlpsher1

RussellS wrote:"The coroner determined the crack... and deemed it an "inclusion flaw" from the manufacturing process."

I took this from the article. Inclusion flaw from the manufacturing process would indicate the part was built with an inherent flaw. So the fork could have broken in the first mile or the 10,000th mile, as happened here more or less. But after 10-20-30 thousand miles of use, it would be awfully hard to argue the part was built with a flaw built in when manufactured. The fork broke. Almost everything will break sometime, somehow. I'm sure we could find a broken anvil if we looked hard enough. Unfortunately in this case the guy died.


+1. Metal fatigue probably played a small part but the main reason the part failed is the manufacturing defect. To me adding an expiration date to parts doesn't make sense. Bike parts aren't stressed enough to cause metal fatigue. I'm pretty sure most fatigue related bike part failures (like a cracked frame) are probably caused by manufacturing defect that escaped inspection.

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mpulsiv
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by mpulsiv

Who drew the conclusion that the root cause was the fatigue of fork and/or steerer tube? Did manufacturer invest time and money to study this particular case? I have a good reason to believe that it was human error (mechanic in this case) that didn't use a torque wrench. Next thing you know, steerer tube cracked.

I don't throw my leg over until I fully inspect my bike after it's back from LBS.


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AJS914
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by AJS914

This is a sad tragedy but we all take these risks every time we ride our bikes. Any sort of freak accident or component failure could cause you to go down. 9,999 times out of 10,000 you walk away or have injuries that will heal. And then every now and then, one of us dies....

I'm surprised that it's the coroner's job to be a bike expert and metallurgist.

RussellS
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by RussellS

pdlpsher1 wrote:but the main reason the part failed is the manufacturing defect.


The guy owned the bike for 10 years and I assume he rode it quite a few miles each year. Is that a manufacturing defect? After that much use how can you claim the defect was manufactured into the part? I assume, maybe incorrectly, that a defect manufactured into the bike would cause it to break in the first few miles of use. Not 30,000(?) miles and 10 years later. If your definition of manufacturing defect is correct, then a car that breaks down after 20 years and 250,000 miles of use is defective when it was manufactured. And the manufacturer should be held liable. Nothing can ever wear out or break again.

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Rick
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by Rick

RussellS wrote:"Inclusion flaw from the manufacturing process would indicate the part was built with an inherent flaw.

That is not quite right. There is a certain statistically distributed number of "inclusion flaws" that are standard and expected in any bulk material. They are "inclusion flaws" but not necessarily "flawed material". Sort of like having a knot in a piece of wood. We all know they are there, and they are considered in the safe working loads for the material.
For really critical parts, they can be ultrasonically, or X-ray inspected to reduce ((eliminate) inclusion flaws. But I don't think any bike manufacturer goes to that expense. The objective evidence would be that, since it lasted for many years of riding, it was "fit for the purpose".

pdlpsher1
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by pdlpsher1

RussellS wrote:
pdlpsher1 wrote:but the main reason the part failed is the manufacturing defect.


The guy owned the bike for 10 years and I assume he rode it quite a few miles each year. Is that a manufacturing defect? After that much use how can you claim the defect was manufactured into the part? I assume, maybe incorrectly, that a defect manufactured into the bike would cause it to break in the first few miles of use. Not 30,000(?) miles and 10 years later. If your definition of manufacturing defect is correct, then a car that breaks down after 20 years and 250,000 miles of use is defective when it was manufactured. And the manufacturer should be held liable. Nothing can ever wear out or break again.


Do you expect your frame to last at least ten years? If so why shouldn't the fork last at least ten years?

mattr
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by mattr

pdlpsher1 wrote:Bike parts aren't stressed enough to cause metal fatigue.
Erm, yes they are.

AJS914
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by AJS914

pdlpsher1 wrote:Do you expect your frame to last at least ten years? If so why shouldn't the fork last at least ten years?


We don't know if there was damage caused by installation or damage from a crash during those 10 years. Maybe the stem was over torqued?

We all hope a frame will last 10 years but it may not. That is the nature of mechanical equipment. One could ride an overbuilt 35 pound steel bike that is assured to last 10 years but then it wouldn't be a joy to ride.

Valbrona
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by Valbrona

Fatigue life of aluminium doesn't compare well to other materials. In the case of budget forks that are bonded together, perhaps better to use a steel steerer tube rather than an aluminium one. And a butted one at that.

pdlpsher1
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by pdlpsher1

mattr wrote:
pdlpsher1 wrote:Bike parts aren't stressed enough to cause metal fatigue.
Erm, yes they are.


So which part on your bike do you plan to throw out due to metal fatigue?

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cyclespeed
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by cyclespeed

I remember when I was into MTB a good 10+ years ago and many handlebars were alu, the 'unwritten rule' that did the rounds was to change the bar every 5 years (even for carbon too).

The handlebar is one of the most stressed components on the bike, especially in MTB and undergoes repeated flexing. No aluminium part can withstand that forever, although exactly what the lifespan is is very hard to tell - depends on many things like, how your ride, how thick is the alu, etc. etc.

mattr
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by mattr

pdlpsher1 wrote:So which part on your bike do you plan to throw out due to metal fatigue?
Personally speaking i've thrown out an aluminium frame, a pair of cranks, a stem and 4 or 5 sets of bars. Everything else i've either sold or binned due to incompatibility issues before it failed. Or crashed it.

Even most steel "race weight" frames are so lightly built that they are over the materials endurance limit in normal use, and will (eventually) fail.

by Weenie


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