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 Post subject: Metal fatigue
PostPosted: Sat Jun 16, 2012 12:15 am 
rBoTM Winner
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Joined: Mon Aug 08, 2011 5:58 pm
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Location: Scotland
I have ridden my old training bike (a Peugeot Europa) continuously since about 1990, and the other day I had a strange drooping sensation on my right hand side and blow me if half of my drop handlebar didn't come off in my hands! It got me thinking, how long does this old componentry and frames last? The new 3T bars I got said to replace them after 15000km. I've done about triple that on my old bars - along with the frame. What's the consensus - should I put it out to pasture or continue living in the good old days confident that i'll never build up enough stress fatigue cycles in a brazed steel frame to have to worry about it in my lifetime...?


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PostPosted: Sat Jun 16, 2012 6:55 am 
rBoTM Winner
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Hi, it is plainly down to useage, and storage, metal does fatigue, and under certain conditions, some metals quicker than others. Each metal will have its chemical trigger ( long term stress doesn't help the cause either ) that will start its downward spiral, its just a matter of protection and avoidance. I'm restoring a 1934 bike that has been barn stored in the south of france, and painted over sometime in its history ( another layer of protection ), and its looking like, the bike and most of its components are going to be completely trust worthy for riding. Just some thoughts. Terry


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PostPosted: Sat Jun 16, 2012 11:24 am 
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Joined: Thu Feb 24, 2011 9:54 am
Posts: 2
Location: Australia
im guessing the bars were aluminium? aluminium has 0 fatigue limit/threshold.

which means every time you ride your bike any part made of alu' that flex's even slightly, is working towards the point at which it will fail due to fatigue.

steel/steel alloys are different. there is a point to which steel and flex/bend and be completely un effected.

so.. discounting corrosion, a steel frame, if ridden within its limits, can last (in relative terms) for ever :)


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 Post subject: Metal fatigue
PostPosted: Sat Jun 16, 2012 11:45 am 
Retro Guru

Joined: Wed Nov 24, 2010 4:38 pm
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Location: The Lovely Lincolnshire Wolds and by the sea in Sussex
531 pro wrote:
I have ridden my old training bike (a Peugeot Europa) continuously since about 1990, and the other day I had a strange drooping sensation on my right hand side and blow me if half of my drop handlebar didn't come off in my hands! It got me thinking, how long does this old componentry and frames last? The new 3T bars I got said to replace them after 15000km. I've done about triple that on my old bars - along with the frame. What's the consensus - should I put it out to pasture or continue living in the good old days confident that i'll never build up enough stress fatigue cycles in a brazed steel frame to have to worry about it in my lifetime...?


Be interesting to know what make of bars snapped on you. Had they been crashed previously and bent back to their original shape, did they have a ferrule?

I am still riding many bikes with old dural bars (GB, ITM, Cinelli)...some owned from new, I am not a light rider and have never had or suspected a problem - my thoughts would be this is unusual, hence my question about the contributing factors (before we get too technical about fatigue etc).

Roadking.


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 Post subject:
PostPosted: Sat Jun 16, 2012 1:06 pm 
rBoTM Winner
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Joined: Tue Mar 27, 2012 9:28 pm
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Location: Mansfield Woodhouse, Nott's.
Many years ago i was sat at some traffic lights and when the lights changed i pedalled off and got out of the saddle
only for my two month old brand new Cinelli stem snap completely off at the expander bolt and i went over my bike
and the broken stem section which was in the headset which stabbed me in my stomach and put me in hospital for a day.

The shop were i got my stem from examined the broken stem and there was a big air pocket were it sheared and snapped off
I was given another stem and a few more goodies for my injuries and the stem went back to the manufacturers.

We heard nothing from Cinelli :roll:


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 Post subject: thanks for the thoughts
PostPosted: Sun Jun 17, 2012 11:00 pm 
rBoTM Winner
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Location: Scotland
Thanks for the thoughts - doesn't sound too common does it: I worked in a cycle shop in my youth (for 9 years man and boy!) and never saw it, so I was a bit surprised and worried. 10 miles previously I'd hit 40mph down a steep hill (yikes). The bars weren't anything fancy, just aluminium with a steel insert for the clamp area. They'd never been bent or re-shaped but they have clattered down the road a couple of times with me underneath them! Thanks again.


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 Post subject:
PostPosted: Sun Jun 17, 2012 11:05 pm 
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Joined: Fri Oct 14, 2011 8:41 pm
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Location: Cumbria
Fatigue and stress corrosion...........it's what limits old planes on how many G they can pull and saw off Liberty ships, the Comet and the Handley Page Victor.....

Bike stuff is very overengineered as there isn't much penalty if it weighs a few more ounces. You were unlucky :(


Shaun


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 Post subject:
PostPosted: Sun Jun 17, 2012 11:28 pm 
retrobike rider
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Joined: Tue Sep 30, 2008 6:25 pm
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Location: Near Wendover Bucks
A slight defect within, or even a small surface scratch can act as a stress raiser that can focus the forces on a seemingly insignificant weakness.

All materials when stressed have an elastic limit beyond which their structure will be permanently damaged though not broken. Repeated stresses and accumulated damage can cause failure. So the maximum loading on a component should be calculated so as not to exceed the particular materials elastic limit.

Last year I broke a steel bottom bracket axle that had been on my bike for 23 years. There had been a small stress raiser on the axle. This caused a small crack to form that took all those years to work its way across the axle.


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PostPosted: Mon Jun 18, 2012 12:19 pm 
Dirt Disciple

Joined: Sat Jun 18, 2011 7:19 pm
Posts: 92
Location: Scottish Borders
531 pro wrote:
10 miles previously I'd hit 40mph down a steep hill (yikes).


Yikes indeed! This is precicely what happened to my riding buddy a couple of months ago. Near the end of an 80 mile ride, very close to home, his bar snapped close to the stem, very soon after a hairy fast downhill. T'would have been a disaster if it'd snapped then.


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 Post subject:
PostPosted: Tue Jun 19, 2012 9:55 am 
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Joined: Fri Mar 12, 2010 11:24 am
Posts: 354
Location: London
I read a comment in the comic from Sean Yates once, that he regularly bent his handlebars when trying hard. He wasnt boasting , just stating that he had to change them on a regular basis because they drooped.


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