Cracks in Carbon

Headhuunter

So as I hurried to a club run a couple of weeks ago I came off the bike. My fault really, I was trying to cut round a load of queuing cars to get to the front of a traffic lit junction so that I could get away before them and avoid having to wait whilst they fannied about in the road turning right and left etc etc.

Anyway, as I skirted round the cars, another car turned into my path and came along the other way, I was slightly across the white line and he was driving very close to it so we both braked and stopped but as I was clipped in, I keeled over, unfortunately onto the drive train side of the bike. The rear derailleur was a bit scratched but seems to work fine still but I noticed v thin hairline cracks in the carbon above the derailleur.

I have ridden the bike since, in fact yesterday I did a fast 65 mile ride with the club, stopping to check the cracks every now and then. I also checked thoroughly once I got home, but it doesn't seen to have changed or get any worse.

So my question is, should I now be scrapping the entire frame for safety's sake, or has anyone else ridden a carbon bike with slight cracks? I really don't want to just chuck the bike away after less than 2 years, and the cracks are tiny....

Fogliettaz

Tap the tubes and see if there is any difference between the stays.

carbonfiend

I recently chipped my S Works top tube carshed racing and shifters hit the tube. I repaired it myself. There are two carbon companies one called Carbonology and the other carbon Mods they sell repair kits which includes Epoxy resin and carbon weave. I spoke to the guy at carbon mods (they specialise in carbon fibre for all industries) and he talked me through what to do it was a piece of piss, just mix the resin drop or wrap the fibre round let it dry trim with stanley knife then sand down. Almost all carbon is repairable apart form catastrophic failure and yeah I know two people that race CF frameswith cracks both off road as well and I have seen repairs of frames with big cracks

Headhuunter

Fogliettaz wrote:

Tap the tubes and see if there is any difference between the stays.

I actually tried pulling on the tubes to see if there was any flex and to see if the cracks moved, but it was completely rigid and the cracks stayed the same. They are very small cracks, less than the width of a human hair.

itchieritchie

Interesting topic, and one that also applies to me.

I have a Focus Izalco Expert 2007, carbon frame and forks. I took the forks off to fit them to a steel Genesis Flyer singlespeed, my hack bike.

I was "flying" down Old Street and it was starting to drizzle. That half light that you get around 5pm in November, following closely behind a car. I spun round to see what the car next to me was up to, and in the split second my head was turned, the car in front loomed large in front of me. With only a front brake I had no chance and took out his entire light clusters.

The bike flipped in the air one way, I tumbled the other way and came down hard. The forks suffered a hairline crack, similar to the one you described Headhuunter, but I've ridden the bike almost daily since, with no apparent ill effects, even with the potholes we get around London.

Maybe I ought to be sensible like carbon fiend and get them checked out and/or repaired, but there is no discerniblly extra flex from the forks, and they feel just as solid as ever.

Don't chuck a good bike away, unless you've had it checked out and an expert says you should...!!

Just my tuppence worth, hope that helps. Cheers for the tips carbonfiend, may well check those companies out.

Good luck.

Headhuunter

carbonfiend wrote:

I recently chipped my S Works top tube carshed racing and shifters hit the tube. I repaired it myself. There are two carbon companies one called Carbonology and the other carbon Mods they sell repair kits which includes Epoxy resin and carbon weave. I spoke to the guy at carbon mods (they specialise in carbon fibre for all industries) and he talked me through what to do it was a piece of wee-wee, just mix the resin drop or wrap the fibre round let it dry trim with stanley knife then sand down. Almost all carbon is repairable apart form catastrophic failure and yeah I know two people that race CF frameswith cracks both off road as well and I have seen repairs of frames with big cracks

That's very interesting, thanks. I'll look into it

Escargot

I'm sure there will be a fracture mechanics specialist on here somewhere that will give you a more detailed opinion but personally I'd have thought it very much depends on how deep the crack is.

I work with 0.3mm thick carbon sheets and at that thickness it is almost impossible to tell if the sheet has failed (eg if a spanner is dropped onto a sheet by accident) without using specialist equipment.

A hairline crack will tell you next to nothing about the severity of the crack. I apologise for the 'doom and gloom' response but I don't think it's possible to say with any certainty if it's easily repairable or not.

Rockhopper

Thing with carbon though is that when it does eventually fail it won't give you any warning.

Gav2000

Could the crack be in the paint on top of the carbon rather than the carbon itself?

Gav.

RedJohn

itchieritchie wrote:

Don't chuck a good bike away, unless you've had it checked out and an expert says you should...!!

Preferably an expert, or two, with no interest in flogging you a new bike!

Headhuunter

Gav2000 wrote:

Could the crack be in the paint on top of the carbon rather than the carbon itself?

Gav.

There's no paint on carbon, but I suppose there must be a layer of varnish or something. Could be that I suppose, I just don't know. I'll have to try to find an independent carbon checking bod or something...

Escargot

itchieritchie wrote:

The bike flipped in the air one way, I tumbled the other way and came down hard. The forks suffered a hairline crack, similar to the one you described Headhuunter, but I've ridden the bike almost daily since, with no apparent ill effects, even with the potholes we get around London.

Maybe I ought to be sensible like carbon fiend and get them checked out and/or repaired, but there is no discerniblly extra flex from the forks, and they feel just as solid as ever.

Please bear in mind that your forks may not feel any different and by hand it is unlikely that you will be able to tell whether one fork is any more/less flexible than the other (it will be that subtle).

Also cracks take time to propagate and it is the fatigue i.e. constant cycling of stress, that may eventually cause failure. The closest analogy I can think of is cutting tiles as carbon is similarly a brittle material. You only need to make the smallest score line in a thick tile but when loaded will fail suddenly. Rockhopper is quite right by saying that it won't give you any warning.

However what you can see as a hairline crack could well be nothing and having thought about it, it could be the lacquer ?

Please for your own safety get the bike checked properly by an expert. Best of luck

HonestAl

here's what might be a daft idea. If the cracks are as shallow as you think, then it's possible they're just in the laquer layer. So how about carefully polishing the area with some fine wet and dry... if they're just in the paint they'll vanish pretty soon, then you can just repair the laquer , maybe even just T- cut it a bit... If they're still there, then they might be a bit more significant, then you can perhaps take some of the repair advice?

just a thought...

bikerZA

I would be very, very careful riding a bike with a potentially cracked frame. Definitely get your LBS, preferably one that deals in your bike brand, to check it out. I wouldn't ride it until you have the all-clear that it is just a crack in the lacquer or the like.

Tom Butcher

There is no way on earth I'd ride a pair of forks with hairline cracks that developed after a crash. They may be the laquer but why risk it for the cost of a pair of forks - I binned a pair for similar reasons after a stack in the Fred Whitton sportive some years back.

Small cracks above the derailleur maybe a bit different - depending on the position - still potentially dangerous though but maybe less so and with it being a more expensive a carbon repair kit to reinforce it might be the way to go.

bigkid

Like HonestAL says it is easy to check if the cracks are in the laquer, just carefully sand it away using 1000 wet and dry or higher.
You can confirm if there are any cracks in the un-laquered carbon using brake cleaner. Spray it on and watch as it evaporates, any cracks will 'hold' the brake cleaner and appear wet.
I would definitely check it thoroughly as you don't really want to be taking any chances. If you are lucky you only have a small area to re-laquer if not then do some research into repair options that suit you the best (DIY?)

bigkid

Certainly is, and might only be a problem for the laquer (easily checked) and not for the composite. Solvents are used regularly during the manufacture of the frame.

Monty Dog

I don't know many LBS that have sufficient expertise to be able to undertake NDT on a composite structure - the only effective techniques are ultrasound or x-ray - not the kind of stuff your LBS is equipped for - they usually send it back to the maker of distributor who aren't much cop either. You could do a DIY NDT - apply a spirit-based coloured marker pen over the affected area - red or blue are quite visible. Use the wet-and-dry to remove the local lacquer/paint from the area. Try and wipe away any coloured traces of the marker - if there is a crack, you will not be able to erradicate the coloured ink as it will have penetrated the crack. The pros use ultraviolet inks and lights.

bigkid

djbarren wrote:

are you sure, as far as i know solvent based products are not to be used on carbon fibre once it is a cured state. will check this out and report back

I can assure you the only thing you might of heard of is to be careful on painted/laquered composite parts. oh and definitely on un-cured! Trust me.