Accident damage.

Goodaye, I was involved in a crash racing last week and hit a rider fairly hard. I took my bike to a bike shop so they could check for any damage and they gave it back saying it was OK. On further inspection today I have found a crack about 4 mm long in a L shape in the paint on top of the right fork. My bike is a Look 585 team issue with the HSC 5SL Forks.
I have heard all sorts of stories about how carbon frames will normally crack right through and not start as a small crack, so hopefully it is the paint.

I thought I would post this on the forum to see what experiences everyone has had with damaged carbon frames. I have raced steel all my life so I am a bit concerned as to what step I should take next.
Also if I need to replace the forks where can I purchase them in the white team colours.

Thanks in advance for any replies.

Getting an L-shaped crack in CF would take some doing, so odds are that you're looking at a scratch in the paint instead. One thing you can do is to flex the fork and see if the suspected crack changes. You might need to get someone to help you out in order to be able to push/pull and look at the same time. No movement, no worry. If there is movement next step would be to carefully remove the paint at the damaged site to be able to look at the structure below. If you have a spot where paint adhesion is poor you might have a large flake that is shifting ever so slightly when the fork flexes.

I'm sorry to hear about your accident. I hope you're okay and that nobody got too seriously hurt.

As for your fork, I'd be very cautious. A crack in the paint could very well be an indication of damage underneath. Please, take your bike back to the shop and show them what you found. A crack in the paint after a hard crash is very suspicious.

Carbon fiber composites can have cracks, voids and other damage on internal layers that does not extend out to the final or cosmetic layer of the layup. This can make inspection very difficult and can result in sudden, catastrophic failure as the final layers of the composite give way. The only reliable methods of inspection that I know of are ultrasound and dye penetration testing. Even then, the composite used in a bicycle is so thin that you might miss something.

If it were me, unless the shop could give me some peace of mind (i.e., show that it was a case of obvious paint flaking, etc) I would buy a new fork. Sudden fork failure often causes a crash that has the rider landing on his face...

John Swanson
www.bikephysics.com

I agree, spending $200US on a new fork seems like cheap insurance to me. The risk, taking a header when you are going 40mph on a downhill, seems like the health bills would be a whole lot more money.

Tap a quarter (or similar object) over the crack, and then over a different area of carbon. Compare the sounds. If the carbon is compromised it will have a very heavy, dead sound to it. Best would be to have a bike shop take a look/listen. They will have more experience and know what to look for.

Thanks for the replies, the forks are definitely cracked so it pays to check the bike yourself. I still don't know how the bike shop missed it !, you would think the top of the forks would be the first place to look when you T-Bone a fellow rider at 45-50ks.
Anyway now I am after a set of Look HSC 5SL forks in white team colours. May need to take out a second mortgage to pay for them!

Thanks again.

Good you checked it carefully and have decided to get a new fork. I'm surprised the LBS would miss it. Normally LBS here tend to error on the side of caution when it comes to checking crashed parts, explaining that they don't want to take on any liability by pronouncing a part OK.

Curious if you tried the coin-tap test that toffoisme outlined? Before ultrasonic inspection equipment came along, tapping was used extensively on composite aircraft panels as the way to detect debonding. Don't know if it would work on small cracks in CF forks though. Would appreciate your input.

I doubt that the coin tapping thing would work. What you'd be listening for is the hollow sound of a void, which could work for large structures and large voids. In a bicycle, the laminates are only a millimeter thick and any cracks or delaminations are correspondingly small.

Even in large structures I've been told that the only reliable methods to check for damage in carbon are ultrasound and dye penetrant testing.

John Swanson
www.bikephysics.com

You should also replace your helmet if it hit the ground, even if no damage is visible

How long have you had your bike? you might be able to sneak away with getting them replaced by warranty.
Just remember you were riding along minding your own business when you went over a bump and your fork made a funny noise!

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