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carbon crank scratched - concern?



 
 
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Old May 12th 20, 06:23 PM posted to rec.bicycles.tech
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Default carbon crank scratched - concern?

On Monday, May 11, 2020 at 11:08:36 PM UTC-7, 2wheelfan wrote:
On Sunday, May 10, 2020 at 7:34:19 PM UTC-4, wrote:
On Sunday, May 10, 2020 at 4:25:58 PM UTC-7, Sir Ridesalot wrote:
On Sunday, 10 May 2020 17:45:33 UTC-4, 2wheelfan wrote:
On Friday, April 24, 2020 at 4:41:10 PM UTC-4, Ted Heise wrote:
Hi all,

A couple of days ago I noticed a scratch on a carbon crank. Pics
are he

http://www.panix.com/~theise/IMG_7765.jpg

http://www.panix.com/~theise/IMG_7766.jpg

It's on my tandem, so I'm especially senstive to safety. The
scratch does not feel as if it has much depth to it. I think it
may have happened when I lost my balance getting off, and could
potentially have banged it with the Speedplay cleat on the bottom
of my shoe.

Should I be concerned about failure?

As an aside, I wasn't paying enough attention when I ordered this
bike. I specifically wanted titanlum for resistance to cosmetic
damage, but would have preferred *not* to have carbon components
(also for resistance to handling damage).

Thanks for any advice!

--
Ted Heise West Lafayette, IN, USA

I have worked in composites, including carbon fiber layups, and don't believe you have anything to worry about. Boeing's carbon fiber layups approached a proven maximum of 1 million lbs. PSI tensile strength.

Carbon fiber is truly a miracle. Carbon is a miracle. Diamonds are a miracle.

Drifting just a little, I remember hearing on PBS that H2O is the secret of life. Well, not exactly. C is the secret of life. What can hydrogen and oxygen do without carbon?

Do you think that bicycle manufacturers use the same materials as Boeing does?

Cheers


The material is the same. The procedures are FAR different.


There you go. I remember Boeing's layups were very sophisticated vacuum-bagged with heat, sometimes pre-preg, and stringent conditions. But even shadetree carbon layups often attain tremendous tensile strength that boggles the mind.

In the late 80's we had this aircraft builder running a stress test on WLAC White Lightning composite e-glas wings with wet tubular carbon fiber main spars. After he reached 10 "G" forces* by piling sandbags on the inverted wings he kept on going and one of the wings "blew" with an explosion that unloaded considerable energy and sounded like dynamite. That was an expensive little bit of destructive testing.

*Weight of the loaded 4-place aircraft x 10


Aerospace carbon fiber has two differences - the resins used and the intense compression putting more carbon fiber per square inch into the layup. There are in essence only two types of carbon fiber - woven cloth and wave-woven which is much denser but exactly the same carbon threads.

CF is easy to work with to get good results. The problems is that you can also easily get bad results because the method of building bike frames (or rims) in China leave room for voids which destroy the homogeneity of CF which is absolutely necessary to have strength of the layup.

I have bought many sets of wheels from China now and one wheel out of many delaminated along one wall of a wheel from voids.
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