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Bent carbon frame?



 
 
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  #11  
Old July 9th 18, 10:46 AM posted to uk.rec.cycling
jnugent
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Posts: 10,223
Default Bent carbon frame?

On 09/07/2018 07:08, Ian Smith wrote:

On Sun, 08 Jul 2018 14:29:15 +0100, Peter Parry wrote:
On Sat, 7 Jul 2018 12:38:15 -0700 (PDT), wrote:

Cue a new rear mech and a spoke BUT a LBS insisted that the carbon
frame is also bent and they won't put it in a jig to straighten it.
How can a Carbon stay bend?


Stress any material beyond its elastic limit (yield strength) and it
will deform and stay deformed. You can't bend it straight again..


Really.

What do you think the yield stress of, say, a china plate is?
Do you think you can bend that so it stays bent?


He didn't say "bent". He said "deformed". A stressed china plate will
certainly be that.

And any material bent plastically stays bent forever. Hmm.


Maybe.

PS: You can learn something every day. "Plastically" was a new one on
me, but there are 636,000 instances of it on UK Google. Thanks for that.
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  #16  
Old July 9th 18, 05:37 PM posted to uk.rec.cycling
TMS320
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Posts: 2,285
Default Bent carbon frame?

On 09/07/18 15:42, JNugent wrote:

The much-maligned Wikipedia is very useful, isn't it?


Is this your second source of information (after this newsgroup) for
your in depth knowledge of modern cyclists?

  #17  
Old July 9th 18, 10:38 PM posted to uk.rec.cycling
Ian Smith
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Posts: 3,587
Default Bent carbon frame?

On Mon, 9 Jul 2018 02:51:24 -0700 (PDT), wrote:
On Monday, 9 July 2018 07:08:32 UTC+1, Ian Smith wrote:
On Sun, 08 Jul 2018 14:29:15 +0100, Peter Parry wrote:
On Sat, 7 Jul 2018 12:38:15 -0700 (PDT),
wrote:

Cue a new rear mech and a spoke BUT a LBS insisted that the carbon
frame is also bent and they won't put it in a jig to straighten it.
How can a Carbon stay bend?

Stress any material beyond its elastic limit (yield strength) and it
will deform and stay deformed. You can't bend it straight again..


Really.

What do you think the yield stress of, say, a china plate is?
Do you think you can bend that so it stays bent?


Doesn't every material have an "elastic limit"?


Most materials have a limit to elastic behaviour. They don't all
yield when they reach it - some are almost perfectly elastic until the
point where they shatter into thousands of pieces. A dinner plate
doesn't reach a iield strnegth, then deform and stay defomred -
doesn't "deform", it shatters.

Many materials that do yield don't have a yield 'point' - even
relatively common stuff like stainless steel doesn't have a defined
yield point - it doesn't exhibit a pure elastic behaviour except at
infinitesimal strains.

regards, Ian SMith
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  #18  
Old July 10th 18, 01:05 AM posted to uk.rec.cycling
jnugent
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Posts: 10,223
Default Bent carbon frame?

On 09/07/2018 17:37, TMS320 wrote:

On 09/07/18 15:42, JNugent wrote:

The much-maligned Wikipedia is very useful, isn't it?


Is this your second source of information (after this newsgroup) for
your in depth knowledge of modern cyclists?


It was not I who quoted that site.
  #19  
Old July 10th 18, 07:43 AM posted to uk.rec.cycling
TMS320
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Posts: 2,285
Default Bent carbon frame?

On 10/07/18 01:05, JNugent wrote:
On 09/07/2018 17:37, TMS320 wrote:
On 09/07/18 15:42, JNugent wrote:

The much-maligned Wikipedia is very useful, isn't it?


Is this your second source of information (after this newsgroup) for
your in depth knowledge of modern cyclists?


It was not I who quoted that site.


Nor did I. Has it got much to say about evil cyclists?
  #20  
Old July 10th 18, 09:18 AM posted to uk.rec.cycling
Bret Cahill
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Posts: 646
Default Bent carbon frame?

On Monday, July 9, 2018 at 2:34:46 AM UTC-7, wrote:
On Sunday, 8 July 2018 23:18:39 UTC+1, TMS320 wrote:
On 08/07/18 15:48, wrote:

STOP PRESS - It is the Al dropout that is bent and it can be unbent, thankfully.


Al is not good once elastic limit has been exceeded. Unlike steel. But I
guess that since it is an insert, rather than an integral piece of frame
it is not so critical.


The carbon bits of the frame end at the wheel dropouts which are aluminium. It is only the rear mech hanger bit which is bent so it can be gently eased back which is good news.

Here is a Carbon frame that has been in a real crash - as can be seen, they don't really bend as such.

https://pbs.twimg.com/media/Dhp1wzMWsAIcMUf.jpg


Shortly after 9/11 a sub contractor tried to repair a carbon wing or tail section like it was a surfboard ding. Apparently composite materials in modern commercial air craft is a little more complicated than that. The air liner crashed in NY City killing all on board. The NTSB & FAA were really good telling everyone it wasn't terrorism so don't worry about it.

If you do the same thing with a damaged carbon bike frame, be careful when you first try it out. Don't start off pegging curbs, pot holes, RR tracks, etc.


 




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