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Cycle Fatigue, Metal Fatigue

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Cycle Fatigue, Metal Fatigue

Old 11-22-16, 05:04 PM
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hotbike
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Cycle Fatigue, Metal Fatigue

Should there be a 'safe' life for bicycle parts? Coroner raises questions after death of cyclist Richard Stanton

Quote:
"....But a hidden flaw in his $4000 bike, undetectable by mechanics, would mean the Canberra father would never make it to his 50th birthday.

Mr Stanton was killed after the alloy steering tube in his bicycle "unexpectedly and catastrophically failed" in January 2015,..."

Cycle Fatigue, Metal Fatigue...

I have noticed a lot more recalls lately, for handlebars...
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Old 11-22-16, 05:14 PM
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George Hincappie took a tumble into the drainage ditch along one of those Cobbeled sections of Paris - Roubaix..
His Aluminum fork steerer Broke. the engineers worked on a More forgiving, compliant rear ..

and Pros Get a fresh Bike several times a season. Next trick is the tapered Steering tube with a 1.5" lower bearing..

Aluminum Steerers have been Known to do that , steel it's so much less Unlikely.

Airplanes have Flight Hours once they hit that max, they park them in the desert..

Going for super Light has a shorter lifespan ..



...
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Old 11-22-16, 05:17 PM
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I can only say that I am glad that its Austrailia rather than the U.S.
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Old 11-22-16, 05:33 PM
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I don't have a good answer for this but as someone who has broken four frames and one crankset in the past 4 years/33,000 miles this is something I think about quite a bit.

What I'm left wondering is the risk for this any greater than random chance?

Anyway, sad story.
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Old 11-22-16, 05:40 PM
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I guess this would be the definition of "stupid light".
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Old 11-22-16, 06:01 PM
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Originally Posted by fietsbob View Post
George Hincappie took a tumble into the drainage ditch along one of those Cobbeled sections of Paris - Roubaix..
His Aluminum fork steerer Broke. the engineers worked on a More forgiving, compliant rear ..

and Pros Get a fresh Bike several times a season. Next trick is the tapered Steering tube with a 1.5" lower bearing..

Aluminum Steerers have been Known to do that , steel it's so much less Unlikely.
I've only had a steel steerer snap (and still have some minor scars 40 years later). The aluminum steerer on my current bike has many times the mileage and time of that steel one.

The story and recommendation of the coroner seems a little odd. After concluding that the failure was due to a defect in the original manufacturing process he wants the industry to set time limits on use? Seems to me that products built with initial defects could fail at any time.
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Old 11-22-16, 06:18 PM
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By definition, all materials contain defects at some level. Fatigue is the occlusion of those defects under cyclic (repeating) stress into a crack that will grow under normal (design) cyclic stress.
That crack, which will grow at the normal stress, is defined as a critical flaw size.
Steel has the property of endurance limit, in that, at or below the endurance stress, microscopic damage will not accumulate into a critical flaw (it could at stress higher than the endurance limit). This is because of the crystal system in magnetic steels - they have limited slip systems (body-centered-cubic crystal system).
The aluminum alloy crystal system (face-centered-cubic) has many more slip systems, allowing defects to slide in the metal grains and grow together to form a critical flaw. It may take hundreds of millions of stress cycles to form the critical flaw, but as long as the cyclic loading continues, it will eventually happen.
And it could take longer than your lifetime usage of the part.

The cyclic loading can as simple as your weight on the bars cyclically changing under road vibration - just an example.
Of course rotating stress like pedaling a crank is a cyclic stress.

The moral is you should occasionally replace your aluminum bars. Unfortunately, there is no hard and fast rule about how often that should be.
But if you ride in your core muscles and don't lean heavily on your bars, it's certainly less frequently than if you do. It's also smart to inspect your bars for cracks at any machined lines or loaded edges (such as the corner of stem contact or diameter change in the bar). If you find a crack, replace the bar immediately.

btw, if you search handlebar fatigue, you'll find many articles to read, both practical and academic.

Last edited by bulldog1935; 11-22-16 at 06:31 PM.
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Old 11-22-16, 06:44 PM
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Article says he had a previous minor "prang" on the bike.
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Old 11-22-16, 06:55 PM
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a certain way to accelerate the process
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Old 11-28-16, 08:36 PM
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Originally Posted by fietsbob View Post
George Hincappie took a tumble into the drainage ditch along one of those Cobbeled sections of Paris - Roubaix..
His Aluminum fork steerer Broke. the engineers worked on a More forgiving, compliant rear ..

and Pros Get a fresh Bike several times a season. Next trick is the tapered Steering tube with a 1.5" lower bearing..

Aluminum Steerers have been Known to do that , steel it's so much less Unlikely.

Airplanes have Flight Hours once they hit that max, they park them in the desert..

Going for super Light has a shorter lifespan ..
There are lots of things that can make the steer tubes stronger. Larger diameters. Thicker materials. Tapers, butted - thick at the bottom, thin in the middle, etc.

There is so much emphasis on lighter the better.

Plane manufacturers are required to test their airframes with an accelerated testing system (which helps determine the fatigue lifespan).

Perhaps bike manufacturers should have similar testing. Wiggle and jiggle the frames 24 hrs a day. Drop them against steel posts. Simulate crashing into parked cars... Heat, Cold, & UV Exposure, etc. Learn from the mistakes, and not only make lighter bikes, but also stronger bikes.
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Old 11-28-16, 09:23 PM
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Originally Posted by CliffordK View Post
There are lots of things that can make the steer tubes stronger. Larger diameters. Thicker materials. Tapers, butted - thick at the bottom, thin in the middle, etc.

There is so much emphasis on lighter the better.

Plane manufacturers are required to test their airframes with an accelerated testing system (which helps determine the fatigue lifespan).

Perhaps bike manufacturers should have similar testing. Wiggle and jiggle the frames 24 hrs a day. Drop them against steel posts. Simulate crashing into parked cars... Heat, Cold, & UV Exposure, etc. Learn from the mistakes, and not only make lighter bikes, but also stronger bikes.
This would kill the boutique makers. I vote no.
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Old 11-28-16, 10:32 PM
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As Yogi might have said "it's Deja Vu all over again".

There was a thread about this a few days ago. I posted to it, and was trying to find it and link or ask the mods to merge it. Looking at the dates, I'm wondering if it's this one, and it's been truncated pretty severely.

Anyone else remember, or am I suffering reverse senility and remembering things that never were?
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Old 11-28-16, 10:42 PM
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Originally Posted by FBinNY View Post
As Yogi might have said "it's Deja Vu all over again".

There was a thread about this a few days ago. I posted to it, and was trying to find it and link or ask the mods to merge it. Looking at the dates, I'm wondering if it's this one, and it's been truncated pretty severely.

Anyone else remember, or am I suffering reverse senility and remembering things that never were?
Yep, I remember it, too: https://www.bikeforums.net/classic-vi...r-article.html
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Old 11-28-16, 11:02 PM
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Yep, started the same day. It was he date that had me wondering.

I never thought to look for this in C&V. Thanks.

BTW - if bike makers start talking about useful service life, then there may not be C&V anymore.
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Old 11-29-16, 12:26 AM
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Originally Posted by howsteepisit View Post
This would kill the boutique makers. I vote no.
There are only a couple of boutique builders working in CF and Aluminum, although perhaps a few more that are adding commercially available CF forks to their custom frames.

The UCI is supposed to be certifying frames, wheels, and forks.
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Old 11-29-16, 12:37 AM
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Originally Posted by FBinNY View Post
Yep, started the same day. It was he date that had me wondering.

I never thought to look for this in C&V. Thanks.

BTW - if bike makers start talking about useful service life, then there may not be C&V anymore.
I am very happy with my recently built up C-40. However, the service life of CF fames and components, and purchasing used components is frequently a hot topic on this board.

A rider can recover from many failures. For example a broken spoke generally doesn't cause a crash. Perhaps even a broken crank or bottom bracket. But a sudden break of a fork is a downright scary proposition. And, at least the steer tube is completely hidden except during a complete rebuild. Perhaps one should at least consider the service life of the fork, and replace after a decade or so depending on the materials and construction.
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Old 11-29-16, 12:56 AM
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Fun read on steerer tube failure. Not a design issue, a routine shipping issue.

Cervelo founder calls for industry-wide fork steerer test | VeloNews.com
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Old 11-29-16, 01:18 AM
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I bought a nashbar bike twice, same model, and both arrived with what I considered to be minor shipping damage.

There were chips in the paint of the fork and the bottom of the seat post had been rubbed bare, rubbing along...something.

It was weird. Both bikes, same damage, same spots. And it appeared as if the bike had been boxed with some care: glued and stapled box, all of the tubes wrapped with light foam, wheels boxed with protective tabs. But somehow just a bit of exposed metal on the fork and seat post were enough to get them dinged.

UPS btw is known for big time abuse of shipments. They just don't care.

I guess the moral of the story is: don't buy super light bikes.

Anyway, it seems like it's not an issue of gradual, minor accumulation fatigue failure but of of a break in an area which never gets inspected.
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Old 11-29-16, 04:54 AM
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Originally Posted by howsteepisit View Post
This would kill the boutique makers. I vote no.

Nah, that's easily managed.
Assign a test program proportional to the number of frames/parts made.
Shouldn't be too hard to come up with a reasonably fair definition of what's large-scale and small-scale production.
Or an intermediate stage or two.
As a customer you then get the choice.
If you buy the one-off, you do it solely on the trust in the manufacturer.
If you buy a limited edition, then maybe some 3rd party structural analysis.
If you buy a big seller, you get something that's been tested to destruction under lab conditions.
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Old 11-29-16, 07:58 AM
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The article cites: "...failure of the carbon fork on a fatigue fracture in the aluminium steering tube".
Although tests on Stanton's fork may have yet to be done (or revealed), it is obviously significant, in terms of documentation, whether his aluminum steerer cracked, or his aluminum steerer separated from its bond with the carbon crown.
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Old 11-29-16, 09:22 AM
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how do you control the users to retire a part after a fixed number of hours of use?
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Old 11-29-16, 12:29 PM
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Originally Posted by dabac View Post
Nah, that's easily managed.
Assign a test program proportional to the number of frames/parts made.
Shouldn't be too hard to come up with a reasonably fair definition of what's large-scale and small-scale production.
Or an intermediate stage or two.
As a customer you then get the choice.
If you buy the one-off, you do it solely on the trust in the manufacturer.
If you buy a limited edition, then maybe some 3rd party structural analysis.
If you buy a big seller, you get something that's been tested to destruction under lab conditions.
If you buy a bike from ME, it isn't even a Beta-Version yet , YOU will be testing it "to destruction", you will have to sign a non-disclosure agreement, I can always increase the thickness of the fiberglass at any given point on the frame. When it's "perfected" , Then we'll do a carbon fiber version...
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Old 11-29-16, 01:06 PM
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Originally Posted by fietsbob View Post
how do you control the users to retire a part after a fixed number of hours of use?
Never mind controlling them, how do you provide them with a tolerably user-friendly chance of retiring the part(s)?
Most of my bikes don't have bike computers. And I'm not big on diaries or logbooks.
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Old 11-29-16, 01:21 PM
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Originally Posted by 1989Pre View Post
The article cites: "...failure of the carbon fork on a fatigue fracture in the aluminium steering tube".
Although tests on Stanton's fork may have yet to be done (or revealed), it is obviously significant, in terms of documentation, whether his aluminum steerer cracked, or his aluminum steerer separated from its bond with the carbon crown.
I lost track of it, but there was a followup, referencing expert testimony at the inquest. Of course experts disagreed on whether the cause was a defect of some kind (one found one the other didn't), but it seems clear that the aluminum itself failed, not that it separated from the crown.

You might find a link to that on the other thread on this issue in C&V.

BTW and FWIW the British have mandated cycle life testing on various items, and some time back were looking at revising he standards for aluminum steerers, but I don't know what, if any, changes they considered or made.

Either way, I agree that some kind of minimum standards make sense, but they'll only help prevent early failures. As bikes age the variation in stresses and loads become too great to predict a life which is safe, except for an unacceptably short one. Moreover, there's almost zero odds that consumers would adhere to some kind of must retire standard.
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Old 11-29-16, 01:29 PM
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However, if I were a manufacturer, I might be temped to put a statement in a owners manual that after 5 years a fork should be retired and after that time it is use at the owners risk. Then, at least when a 10-year old bike has a fork failure, then at least there is a partial defense.
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