Carbon - is it really so fragile?

bahzob

The discussion below is the latest of a number that seem to say beware of carbon because its likely to shatter at any moment and needs to be treated with kid gloves at all times.

http://www.bikeradar.com/forums/viewtopic.php?t=12547270

My suspicion is that many of these warning arise from the introduction of the material into bike manufacture, when naturally it can be expected to have problems.

But carbon has been around a while and is now commonly used in applications a lot more safety critical than bikes. Is there any real reason to believe the scare stories about carbon if you are buying components manufactured today?

(For myself I have found that my 2006 vintage carbon seat post, frame and bars have taken everything I can throw at them: including 10,000 miles in all weathers, falls and tours with luggage hanging from said seat post, without any problems. The only bits that have failed have been those made out of good old fashioned metal)

Kléber

You'll find plenty of carbon MTB frames which are tougher than alu, you can do a cross-country ride across rocky slopes without worry. Of course, a bad crash can do damage to any frame but carbon isn't glass, it doesn't shatter on impact.

Pagem

Carbon fiber
Carbon fiber, a composite material, is an increasingly popular non-metallic material commonly used for bicycle frames.[2][3][4][5] Although expensive, it is light-weight, corrosion-resistant and strong, and can be formed into almost any shape desired. The result is a frame that can be fine-tuned for specific strength where it is needed (to withstand pedaling forces), while allowing flexibility in other frame sections (for comfort). Custom carbon fiber bicycle frames may even be designed with individual tubes that are strong in one direction (such as laterally), while compliant in another direction (such as vertically). The ability to design an individual composite tube with properties that vary by orientation cannot be accomplished with any metal frame construction commonly in production.

Some carbon fiber frames use cylindrical tubes that are joined with adhesives and lugs, in a method somewhat analogous to a lugged steel frame. Another type of carbon fiber frames are manufactured in a single piece, called monocoque construction. While these composite materials provide light weight as well as high strength, they have much lower impact resistance and consequently are prone to damage if crashed or mishandled. It has also been suggested that these materials are vulnerable to fatigue failure, a process which occurs with use over a long period of time.[/

Many racing bicycles built for individual time trial races and triathlons employ composite construction because the frame can be shaped with an aerodynamic profile not possible with cylindrical tubes, or would be excessively heavy in other materials. While this type of frame may in fact be heavier than others, its aerodynamic efficiency may help the cyclist to attain a higher speed and consequently outweigh other considerations in such events.

Other materials besides carbon fiber, such as metalic boron, can be added to the matrix to enhance stiffness further.[6]

wikipedia

frankblackcat

Well, with all that info from Wikipedia it's convinced me of the truth, never any doubting that as a definitive referance on anything.

Pagem

wikipedia is fairly accurate, succinct and more importantly sourced.

might i suggest you contribute a little more positively instead of taking the easier option to moan like a bitch?

Monty Dog

Some of the wiki statements are unqualified - such as 'much lower impact resistance' - in comparison to what? 'It has also been suggested..." - by whom? . I've been involved in the design and manufactures of composites since 1989, particularly carbon, as well as having had a carbon-framed bike since 1995, so have a reasonable amount of experience. IME, carbon is far more robust than some of the thin-wall aluminium alloys used in bike frames, and I've never seen anything like the number of fatigue failures in carbon that I've seen with aluminium alloys. Yes, if you crash a carbon frame, it can be fatal - but it'll proably be the same for aluminium, titanium and some steel frames too.

wildmoustache

well said montydog.

there is some great stuff on wikipedia but some rubbish also.

a rational response to the concerns is to look at how many carbon frames and components are out there are what the failure rate is, and what the causes of failure are. Unfortunately data on the latter two are pretty hard to come by. It does seem that carbon fibre, when it does fail, fails with little or no warning and this understandably frightens people a bit, myself included.

But I'm persuaded that it's ok to use carbon fibre by the fact that there are hundreds of thousands of cf bike components out there and i hear (by word of mouth, forums etc.) of relatively few failures. CF bike components, the evidence suggests, have a very good safety record.

John.T

Pagem. As anyone can post on wikipedia it can only be trusted if the article is referenced to the original and you check that to ensure it is quoted correctly. While your post is basically correct it is very non specific as Monty has said. I think Frank was being a little bit flipant and may have his tongue firmly in his cheek. There is no need to get on your high horse about it.

p.3.rider

The problem with carbon fibre is that there is a massive range a quality. Cheap stuff can be more suspect to breakage and other problems (in my experiance as a mechanic and rider) so stick to high quality, well tested stuff like stork, schmolke, syntace, ax lightness and the suchlike.

bahzob

Dont really want this to be a debate about Wikie. Would prefer to keep this fact based. So if anyone can post a similar article concerning carbons impact resistance or otherwise from another source to corroborate those in Wikie then please do.

Alternatively has anyone actually experienced a catastrophic failure from a recently manufactured (say last 3 years) carbon component in circumstances which they could have expected another material to withstand please post here.

aracer

Just to give a counter example; on another forum recently somebody commented on how he'd never trust a cf frame off-road, since his alu frame gets dents in the downtube from rocks thrown up by the front wheel, and a cf frame would be written off by those. My reply was that I actually have a cf mountain bike, and regularly get rock strikes on the downtube (from lumps big enough that I've got bruised toes when they've bouunced off sideways) and not only has it not failed, but unlike his alu frame there is no sign of damage apart from to the cosmetic topcoat.

Not sure I'd like to try bouncing rocks off a lightweight cf road frame (it would damage the topcoat laquer), but I see no reason to expect one to fail in a crash which didn't also cause terminal failure in a lightweight alu road frame.

wildmoustache

there's a bit of an anti-carbon lobby on this forum ... small but occaisonally quite noisy. I can understand that. It's generally pretty expensive and doesn't absolutely revolutionise a bike's performance in the way marketing departments claim. IMO it offers the best combination of characteristics for a road bike, but others think differently.

the "carbon breaks easily" argument is frequently used by the anti-carbon lobby, but the amount of carbon being ridden out there without problems doesn't really fit their theory.

allaction

Its a little bit like the end of a romance; some people look back and remember the good times, some the bad. If all the people who have written off carbon bikes blame it solely on the frame they are the bad times. Then again if the people who wrote off said carbon frame accepted that the exact same thing could have happened if the frame was made out of anything but carbon then they are the good times.

Monty Dog

Yes, lets all get sentimental in the days when your chain stays would suddenly depart from your bottom bracket due to internal corrosion, or fork steerers seperating from the crown - these weren't that uncommon with steel frames.

Kléber

My 1000g MTB frame (and its carbon bars, carbon fork steerer, and carbon bar ends can cope with rocky descents, crashes, drop offs and giant rocks pinging it all the time. No problem. A thin tubed alloy frame would have been written off a long time ago.

Remember, distinguish between good and bad. Some frames are cutting edge, others are duff and it shows. Carbon for the sake of it is no use but where the layering can be done to achieve structural benefits, it is very good. Similarly, it can be reinforced in fragile areas, meaning protection and weight only where you want it. You can't get this with metal frames.

But every material has its own advantages and disadvantages. Each to his own...

giant_man

bahzob wrote:

The discussion below is the latest of a number that seem to say beware of carbon because its likely to shatter at any moment and needs to be treated with kid gloves at all times.

http://www.bikeradar.com/forums/viewtopic.php?t=12547270

My suspicion is that many of these warning arise from the introduction of the material into bike manufacture, when naturally it can be expected to have problems.

But carbon has been around a while and is now commonly used in applications a lot more safety critical than bikes. Is there any real reason to believe the scare stories about carbon if you are buying components manufactured today?

(For myself I have found that my 2006 vintage carbon seat post, frame and bars have taken everything I can throw at them: including 10,000 miles in all weathers, falls and tours with luggage hanging from said seat post, without any problems. The only bits that have failed have been those made out of good old fashioned metal)

'Likely to shatter at any moment'? What utter rubbish!

SteveR_100Milers

I'm not sure that compsite resin/fibre materials suffer from fatigue failure. This type of failure is a feature of metallic materials (that have a crystalline structure, which CF does not) and is a result of continuous stressing (such as vibration) at a sub yield stress (the point a which plastic deformation occurs). I cant recall the precise mechanism as its been quite a few years since i diud anything metallurgical, but IIRC its associated with the gradual build up of dislocations around a stress raiser (such as a particle of impurity). Since an amorphous material like CF is not crystalline, there is no movement of any dislocations within its strcuture, therefore no gradual build up and development of microcracks.

alan_sherman

Carbon failure modes include:

cracks propagating along the join between the re-inforcing fibres and resin,

de-lamination of layers of carbon fibre

or the hard way is when a crack goes across the fibres.


The funniest thing about carbon fibre is that people will happily ride around on carbon fibre forks, yet they get scared by frames, bars, stems and seat posts. The thing on a bike I REALLY don't want to fail is a fork!

cougie

I'm perfectly happy riding a CF frame, forks and seatpost, but I cant see the point of the stem and bars. If my bike falls over then I doubt my carbon bits will hit the deck - but anytime a bike falls over - the bars are gonna take the brunt.
They're not that much lighter and they are many times more expensive. All my alloy bars tell me to replace after a couple of years - if you do that with carbon too - then it gets very expensive.

redddraggon

SteveR_100Milers wrote:

I'm not sure that compsite resin/fibre materials suffer from fatigue failure.

http://scholar.google.com/scholar?q=car ... a=N&tab=ws

Plenty of papers out there on CF fatigue

I'm sure CF can fail by fatigue, CF is effectively a polymer matrix with stiff fibres, and polymers do suffer from fatigue. There are just different mechanisms for failure.

dennisn

My impression is that carbon fiber is much more brittle than the metals used these days.
It will not bend or flex like metal.
Whether or not this is any kind of factor in bike frames appears to be a moot point.
Plenty of good carbon, aluminum, titanium, and steel bikes out there. For my money
they all do pretty much the same thing. The fact that you see many, many, many,
different brands and types out there says to me that no one brand or material really
stands head and shoulders above the rest.

Dennis Noward