Yet another reason to avoid carbon frames

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tim-b
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Re: Yet another reason to avoid carbon frames

Postby tim-b » 11 Sep 2020, 2:23pm

Hi
bgnukem wrote:
tim-b wrote:Hi

Do I detect a bit of materials scientist mischief, Brucey? How is a saddles and seat posts manual relevant to a frame thread?


A seatpost is a tube under stress, rather like a frame tube.

The point is that the article linked to was specific to Ritchey saddles and seat posts. Ritchey's advice is specific to their matrix and manufacturing technique and it's disingenuous to link advice specific to RITCHEY (their capitalisation not mine) to every CF frame out there.
Brucey will know that the matrix used affects the material's properties and that there are umpteen choices of matrix , which is why Lamborghini can produce CF con rods that will be safe in oil, under extreme temperature and pressure
Regards
tim-b
~~~~¯\(ツ)/¯~~~~

tim-b
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Re: Yet another reason to avoid carbon frames

Postby tim-b » 11 Sep 2020, 2:34pm

Hi
Interesting they say 'don't leave in the sun'. I'm thinking of the thousands of carbon hired road bikes in places like Majorca and Lanzarote sitting outside cafes/hotels in the blazing sun! I suppose the hire fleets don't run their bikes for very long though.

The CF is cured under far higher temperatures than you'll find outside a Spanish cafe.
You can lead a cyclist to CF, but you can't make them ride it, so I'll leave you to it
Regards
tim-b
~~~~¯\(ツ)/¯~~~~

Brucey
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Re: Yet another reason to avoid carbon frames

Postby Brucey » 11 Sep 2020, 2:50pm

heating in the sun is always very lopsided; CF absorbs sunlight pretty well, and the heat doesn't always conduct quickly to other parts of the same structure. The result is that a CF part can see quite high internal stresses as a result of uneven thermal expansion. These stresses include through-thickness stresses which otherwise wouldn't occur and it may promote delamination in some cases. In addition some resins are susceptible to UV damage too.

Realistically only a small fraction of CF parts might suffer appreciable damage this way, but if those parts then go on to break in service, the manufacturers have a responsibility to make it clear that this might happen.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

Jamesh
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Re: Yet another reason to avoid carbon frames

Postby Jamesh » 11 Sep 2020, 2:54pm

Probably not a good idea to have a near naked black frame then.....

As is the fashion....

Cheers James

Ontherivet77
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Re: Yet another reason to avoid carbon frames

Postby Ontherivet77 » 12 Sep 2020, 9:24am

Brucey wrote:
Ontherivet77 wrote:Here's a relevant article from cycling weekly:

https://www.cyclingweekly.com/news/late ... ife-277989

The head of engineering from Focus bikes seems pretty confident of the performance their carbon offerings, which is reassuring....


apologies if this seems b-obvious but would he be likely to say anything else....?

Of course not.

cheers


Okay fair enough he's not likely to be impartial, but how do you respond to his comments regards mitigating some of the problems that have been raised in this thread, ie UV damage and corrosion from salt etc.

pwa
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Re: Yet another reason to avoid carbon frames

Postby pwa » 12 Sep 2020, 9:31am

It should be possible to provide adequate UV protection for carbon bike components. After all, many modern aircraft have carbon elements, and they fly for hours on end high up where the air is thin and UV exposure is much higher.

Mike Sales
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Re: Yet another reason to avoid carbon frames

Postby Mike Sales » 12 Sep 2020, 9:35am

pwa wrote:It should be possible to provide adequate UV protection for carbon bike components. After all, many modern aircraft have carbon elements, and they fly for hours on end high up where the air is thin and UV exposure is much higher.


When using epoxy/glass or ply in a boat I always add a final coat or more of UV resistant varnish, if the finsh is not paint anyway.

thelawnet
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Re: Yet another reason to avoid carbon frames

Postby thelawnet » 18 Sep 2020, 8:51pm

This was on a titanium frame.

for2.jpg


Apparently the fork failed cycling along a smooth road with no potholes, and has been found to have catastrophic voids. User has suffered broken neck, paralysis, among other things, and is still in a coma.

Frame builder makes their own Ti, and forks god knows where they come from, but somewhere in China/Taiwan presumably.

peetee
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Re: Yet another reason to avoid carbon frames

Postby peetee » 18 Sep 2020, 10:13pm

thelawnet wrote:This was on a titanium frame.


For clarity, can you confirm what material the fork is constructed from?
Current status report:
Back on two wheels in deepest Pastyland and loving every minute. Mission: to enjoy big, bad hills again.

hjd10
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Re: Yet another reason to avoid carbon frames

Postby hjd10 » 18 Sep 2020, 11:22pm

peetee wrote:
thelawnet wrote:This was on a titanium frame.


For clarity, can you confirm what material the fork is constructed from?

Carbon, there was a post from a cycling forum on facebook explaining the sad events of the rider who rode on those forks. :-(

hjd10
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Re: Yet another reason to avoid carbon frames

Postby hjd10 » 18 Sep 2020, 11:52pm

Brucey wrote:heating in the sun is always very lopsided; CF absorbs sunlight pretty well, and the heat doesn't always conduct quickly to other parts of the same structure. The result is that a CF part can see quite high internal stresses as a result of uneven thermal expansion. These stresses include through-thickness stresses which otherwise wouldn't occur and it may promote delamination in some cases. In addition some resins are susceptible to UV damage too.

Realistically only a small fraction of CF parts might suffer appreciable damage this way, but if those parts then go on to break in service, the manufacturers have a responsibility to make it clear that this might happen.

cheers

Some plastic aeroplanes are affected by sunlight to such an extent that there is a colour palette that you can select for upper surfaces (excludes dark colours like black for example). Each CF design will be different and the technology is moving on. I'm not keen on CF bike frames as it is really difficult to know that damage has occurred or not as the result of what could be considered very minor impact damage. Someone only has to drop a spanner on to an airframe and your into carbon checks to ensure no damage is present underneath in the structure. As most people know this might only require a coin tap test but there are obviously other methods to check.

hjd10
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Re: Yet another reason to avoid carbon frames

Postby hjd10 » 19 Sep 2020, 12:02am

Error

< EDIT : Graham : The DELETE button is the one with the "X" symbol. You can delete your post unless someone posts a reply - which then blocks a delete. >

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RickH
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Re: Yet another reason to avoid carbon frames

Postby RickH » 19 Sep 2020, 3:32pm

thelawnet wrote:This was on a titanium frame.

for2.jpg

Apparently the fork failed cycling along a smooth road with no potholes, and has been found to have catastrophic voids. User has suffered broken neck, paralysis, among other things, and is still in a coma.

Frame builder makes their own Ti, and forks god knows where they come from, but somewhere in China/Taiwan presumably.

They may have been "just riding along a smooth road" when it failed but we have no information on whether the bike had been in an impact in the recent past.

I think one of the big differences with carbon fibre is that it doesn't bend much. People love to show snapped CF frames (there are whole websites devoted to it). The trouble is that many impacts that break a CF frame would have wrecked a steel one. You run into a solid object on the CF frame & it snaps, a similar impact on a steel frame would see the front wheel overlapping the frame or seriously bent frame tubes. Been there, done that with a steel frame (nearly 40 years ago) but never tried it on a CF frame.

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Sweep
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Re: Yet another reason to avoid carbon frames

Postby Sweep » 19 Sep 2020, 3:39pm

RickH wrote:
thelawnet wrote:
I think one of the big differences with carbon fibre is that it doesn't bend much. People love to show snapped CF frames (there are whole websites devoted to it). The trouble is that many impacts that break a CF frame would have wrecked a steel one. You run into a solid object on the CF frame & it snaps, a similar impact on a steel frame would see the front wheel overlapping the frame or seriously bent frame tubes. Been there, done that with a steel frame (nearly 40 years ago) but never tried it on a CF frame.

Isn't bending better than snapping though?
Sweep

thelawnet
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Re: Yet another reason to avoid carbon frames

Postby thelawnet » 19 Sep 2020, 3:45pm

RickH wrote:
thelawnet wrote:This was on a titanium frame.

for2.jpg

Apparently the fork failed cycling along a smooth road with no potholes, and has been found to have catastrophic voids. User has suffered broken neck, paralysis, among other things, and is still in a coma.

Frame builder makes their own Ti, and forks god knows where they come from, but somewhere in China/Taiwan presumably.

They may have been "just riding along a smooth road" when it failed but we have no information on whether the bike had been in an impact in the recent past.

I think one of the big differences with carbon fibre is that it doesn't bend much. People love to show snapped CF frames (there are whole websites devoted to it). The trouble is that many impacts that break a CF frame would have wrecked a steel one. You run into a solid object on the CF frame & it snaps, a similar impact on a steel frame would see the front wheel overlapping the frame or seriously bent frame tubes. Been there, done that with a steel frame (nearly 40 years ago) but never tried it on a CF frame.


There was in fact more information, Viz. the fork had not been overtorqued, was quite new and had not had any impacts. The exact facts will presumably come out in court, but the information provided by the poster was that it had been x rayed and contained internal voids.