Originally Posted by
humboldt'sroads
Ok - so I checked it out under better light...I mean, the cut is 1/2 inch long at most, and looks like it went through paint, but I don't see anything that's obviously a fiber, but the cut really is too small to tell. I can tell that if any fiber got cut, it wouldn't be more than a millimeter or two and one layer thick, and that's a big if, from what I can tell. At this point, I can't afford a new frame, even an aluminum one, so I think I'm gonna ride this and see if it makes any noise and see if the clear coat cracks any.
Further opinions?
Ride it.
Okay a short tutorial on composites. We have been building metal airplanes for 85 yrs and composite ones for 25.There are several types of non destructive inspections you can do for metal (dye penetrant, X-ray, eddy current, etc) but very few for composite structures. Ultrasound is about the only game in town. Also our capability to model composites' behavior under various loads is still in it's infancy. Especially a complex shape.
As a result for aircraft applications (and I suspect bike frames) composite structures are grossly overdesigned. (spacecraft are a different story then most aircraft structures because they will except lower margins to shave a few pounds) If the resin fiber matrix can carry load X, we typically design to twice that due to the uncertainities involved.
How these things typically fail are void propagations between layers, ; i.e. delamination, followed by failures of the layers themselves . Think phone book. No one can tear a whole phone book in half but a toddler can destroy one a few layers at a time once it is "delaminated". Failure across intact fiber layup, i.e. cracking simply never happens unless the loads are horrendous.
So if you want to have a warm fuzzy then get a quarter and do a "tap test". This is what we do with really really expensive composite aircraft structures before we untrasound them. You can actually map the edges of a void pretty well with a quarter. Once we know there is a void we will mark the edges after an ultrasound and check it periodiaclly with a tap test to make sure it isn't growing. Tap the edge of the coin along the frame and it should have a nice crisp click noise in response. If it clunks instead of clicks then that means there is a void underneath. Since the BB and tubing are hollow they will have a drum like response to a degree but a real void sounds sorta dead. Assuming you have had no voids propagated yet, tap the suspect area and listen. Do this occaisionally and as long as it keeps clicking then you are fine. Even if it starts clunking you can probably ride it a very long time before it falls apart.
Yes composite frames fail. Poorly designed, poorly built frames of all kinds fail. But if a composite structure doesn't fail in it's infancy they usually live forever unlike aluminum or steel.
Remember Orville and Wilbur started off building bikes...