The Cracked Carbon Thread

[Oli]

Here is the DBR in question (hiding behind the Bosomworth road bike).

[Joel]

[hijack]

Can anyone offer any thoughts as to why no manufacturer (that I'm aware of, anyway) makes a 13" carbon bike? Just lack of demand?

[/hijack]

Nothing to see here

I'm going to go with low demand and high cost. ie not many people need frames that small and there is generally quite a high cost per mold which is different for every frame size

not the demand for carbon kid bikes

[ape]

I bought a 'cracked' Trek OCLV MTB frame (only $500!) and used it for a whole National Series and a world cup - no worries. Then in 1996 I got my hands on a carbon DBR which developed a couple of small cracks after three years - have carried on using it, mostly for touring and commuting and I'm still trying to finish it off (and even leant it to Oli and Jonty to try and demo it - no luck). At the moment I have a cracked carbon seatpost on my Schwinn - it cracked about 5 years ago and got a bit worse 2 years ago - over-tightening the clamp above the internal seat-post sleeve. Doh! But it still won't fully break (would have replaced it but a 27.0 with set-back is hard to come by).

Conclusion - carbon fails like any other material, but it also has the potential to hang on very well after moderate abuse (like any other material).

Probably helps that I'm only 70kg and have been lucky enough to score high-end carbon (at dirtbag rates).

nice conclusion.., except I'd take it a step further. Carbon has two wonderful characteristics here.., firstly it can fail, and still remain quite intact, and secondly, cracks don't propagate through carbon nearly as well as they do through metals. Because your parts are made from various layers of fibres in different directions, a crack will only travel until it hits a fibre running across its direction... usually a fraction of a mm. As long as you don't exceed the strength of what's remaining, the part won't get any weaker.

[ape]

[hijack]

Can anyone offer any thoughts as to why no manufacturer (that I'm aware of, anyway) makes a 13" carbon bike? Just lack of demand?

[/hijack]

Nothing to see here

well., I work for a manufacturer of carbon things.., (pretty much anything that people want, and have the $$ to pay for).., if you're seriously keen and have a lot (and I mean a lot) of money I could put you in touch with the boss...

you'd probably be looking at ~$2k for moulds, about the same or a bit more on computer modelling, about 1k for the first frame, which may still ride like a dog... (possibly repeated a couple of times until you're happy with how much flex you're after).., (you could skip the modelling, but it'd give a good starting point and reduce the number of dud frames made before getting one you actually like).., subsequent frames would probably be around 1k each... (once all your other small friends decide they want one)..., Naturally these prices are very approximate as I have nothing to do with the financial side of the business apart from occasionally hearing how much projects are worth..., they could be half that cost, or twice it.., but just to give you an idea of what's out there if you're really keen.

This would be using autoclave cured prepreg... one of the highest quality methods of production currently available.., (there are several different ways to produce carbon fibre products all giving vastly different structural properties)

[Simonk]

nice conclusion.., except I'd take it a step further. Carbon has two wonderful characteristics here.., firstly it can fail, and still remain quite intact, and secondly, cracks don't propagate through carbon nearly as well as they do through metals. Because your parts are made from various layers of fibres in different directions, a crack will only travel until it hits a fibre running across its direction... usually a fraction of a mm. As long as you don't exceed the strength of what's remaining, the part won't get any weaker.

True indeed, although when talking 'moderate abuse' I was thinking of small cracks in carbon versus dents in metal. Usually, a crack in steel involves serious abuse (or a decade of moderate abuse with Aluminium, perhaps). Again, results may differ with heavy riders/hucking action. But I agree, once metal starts to crack you need to head to your nearest metal workshop immediately!

[Malcy]

Smashed at the 2010 Karapoti on the rock garden.

Didn't notice til the next day though...

[onyabike]

there maybe some merit in a carbon layered pinata