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When to be concerned with dings/scrapes on Carbon Fiber?(4 posts)

When to be concerned with dings/scrapes on Carbon Fiber?OwenMeany
Nov 20, 2003 5:39 AM
Well, as a result of my crash yesterday, I am going to need a new quick-release. But I did scrape the CF chain stay.

I do not think it is a problem as it seems not to have gone through the clear coating. But it does lead me to ask: When DO YOU become concerned about dings and/or scratches in carbon fiber? I really do not want to have a failure at 45 miles and hour...

Thanks, jb
I remember a story about someone who broke a carbon chain stayandy02
Nov 20, 2003 7:02 AM
It may be just a cycling tall stay but some say a racer fell riding up a mountain by haveing his handle bar caught by a huge ear on a bald guy wearing a dorag and a eye patch taking antidepresssnts. the carbon stay broke but the rider was still able to jumped back to his feet, on his bike and won the race. The big ear I belive but the wining the race seem fishy.
Cool. Sounds familure. nmOwenMeany
Nov 20, 2003 7:56 AM
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For what its worthboyd2
Nov 20, 2003 7:54 AM
JB,

I would look for these things:
1. Buckling (denting) of the carbon tube.
2. Obvious frayed or broken fibers.
3. Delamination of the carbon fiber layers. This can most easily be detected by taping the area with a coin. Listen closley to the ring. Delaminated areas will sound like a dead spot. Broken fibers will also cause a dead sound in the damaged area. This will be your best way of detecting damage.

Absolutely the best way to find damage will be to use an ultrasonic detector. However it is not likely that even frame manufactures have access to one of these machines. Short of ultrasonics NASA has determined that cointap is the best method of evaluating damage in composite structure.

Also I would use a common 5-minute epoxy to cover any deep scratches in the clearcoat. This will environmentally seal the composite and take the place of the clearcoat.

Disclaimer: These are some of the techniques that we use to inspect composite structures in my shop (filamaent wound aerospace structure). Bike makers may have come up with other methods of evaluating damage. I was thinking about something like a bench load test to measure deflection under load, but it would take data from lots of frames and a good fixture so it is not really possible for the end user to do. So all that said the manufactures rep for your frame may be able to help you better then this board can.

JB