Inspecting Carbon Fibre Bike frames

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2 Mar 2009

This was reproduced from a work forum and is an interesting read
NDT Capability when inspecting Carbon Fiber Bike frames.

Carbon Fiber bike frames are very difficult test and for that reason alone, most reputable manufactures will actually just replace the fame under warranty as long as the original owner has not abused the frame.

Checking if a frame is cracked is not that simple, if the crack is thru the full thickness of the carbon fiber there is a good chance that it will appear on a radiograph. However, if the crack does not go thru the full thickness of the carbon, it may still be cracked, however this may not appear on an x-ray.

Additionally Carbon Fiber is highly susceptible to a phenomena called Barely Visible Impact Damage (BVID). The Carbon Fiber looks fine on the surface, however the structural integrity of the fibers below the surface is less than satisfactory. The amount of damage below the surface varies depending on the type and amount of force of the impact. NDT is able to detect this damage using ultrasonic’s, if they have a suitable standard to compare the frame against. If not detected or repaired this can lead to catastrophic failure. Could get really ugly on a downhill run.

For those of you that do ride carbon frames my suggestion is to handle them with great care. If you have had some sort of impact damage or it appears there is a crack on the surface get it checked. Check you warranty booklet and be familiar with what you can and can’t claim.

On another note, Carbon Fiber is also Hydroscopic (absorbs water), therefore if you get a chip in your paint/gel coat get it fixed ASAP, as this also can have detrimental affects to the strength of your frame. Water absorption can cause a corrosion cell to form on those bikes that are glued together to aluminum lugs, or have aluminum lugs as strengthening members under the carbon fiber. I’ve had 3 TREK OLCV 5500 frames replaced for this reason alone.

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