Are carbon fibre and aluminium strong enought to make frames and forks from ?

[snailracer]

Here's a link to an amusingly archaic article about CF from way back in 1968, entitled "The New Steel" :

http://www.flightglo...20-%202417.html

 

[Rohloff_Brompton_Rider]

<bang bang bang> <<<that's my head thumping repeatedly against the keyboard.

lmao....i really am....

 

[Muddy Ground]

Ha ha! I had this same conversation at a cycle show recently. Guy I was talking to had a carbon seatpost but alloy handlebars as they were safer. I trust carbon handlebars but wouldn't have an 'unsafe' carbon seatpost. No sense in either viewpoint. I've a set of carbon forks that I've had for 15 years and they are still absolutely fine.

If you buy from a reputable supplier, then stuff is geneally pretty good no matter what it is made of. Personally I'd not trust the carbon frames on eBay mind....

MG

 

[Wobblers]

Steel is being superseded in planes, but the state-of-the-art 787 Dreamliner still has about 10 tons of steel, compared to 35 tons of CF.
The fuselages of many modern light aircraft are still made of steel frames supporting aluminium panels - steel is still cost-effective if you need to weld parts together.
Some cold-war Soviet warplanes were made almost entirely of steel so they could be mass-produced (and could still fly at mach 3) and are still flying.


CF doesn't suffer from fatigue failures as far as is known. Other, long-term failure modes may exist, nobody really knows for sure.


My point wasn't that CF is somehow intrinsically crap, it's that engineers aren't that good at designing/manufacturing with it, and the service & maintenance aspect barely exists for bicycles - how many bike shops have ultrasonic scanners and endoscopes?

Boeing (787 stringers), Airbus (rudder, tail) and Trek (fork steerers) have all had high-profile failures of CF components. CF failure isn't even new - Rolls-Royce tried and failed with CF compressor blades in their jet engines in the 1960's, which was so disasterous the company went broke.

Those companies are the best manufacturers in their respective fields - if they can screw up their CF designs, that suggests to me that CF still isn't quite ready for the mainstream.


In addition to the CF, the Dreamliner contains about 30 tons of fibreglass (CF's less-pretty composite sister) - a proven, tough material that fails in a non-catastrophic manner.

You'll find that all that steel is in the engines, which have to withstand very high temperatures - something that Al can't do. Ti can, but it's expensive, and the nickel superalloys you find in the turbine stages do better, as they have outstanding creep resistance (they don't deform under load when hot).

You do realise the "glass" bit in fibreglass is in fact, err, glass? And glass reinforced plastic most certainly fails in a brittle fashion. It certainly is not "tough" in the fashion that engineering metals are.

Carbon fibre has been used in aviation for over twenty years now. The main obstacle in its uptake has been expense, retooling and the need to acquire the necessary skills to fabricate large carbon fibre structures. There is one crash that I can think of involving the failure of a carbon part - the failure of the tail section of an Airbus in the November 2001 New York crash. That was a result of inappropriate pilot repsonse to wake turbulence which overloaded the rudder. It broke when subjected to 2.7 times its maximum design load. Aviation experience demonstrates quite clearly that carbon fibre is perfectly safe with the correct design and fabrication.

The failure in the OP was at the point where the steerer tube is subjected to the maximum bending forces from the load applied to the handlebars. It was probably fatigue failure. Ironically the steerer would most likely not have failed had it been carbon fibre, as CF is much more resilent against fatigue than aluminium.

 

[fossyant]

Here we go again.

 

[snailracer]

You'll find that all that steel is in the engines, which have to withstand very high temperatures - something that Al can't do. Ti can, but it's expensive, and the nickel superalloys you find in the turbine stages do better, as they have outstanding creep resistance (they don't deform under load when hot)...

My point was that steel is still used in modern planes, even the brand-new Dreamliner has 10 tons of it.
RR tried using CF in jet engine compressor blades, which don't get hot like turbine blades do, but they weren't up to the job.

...You do realise the "glass" bit in fibreglass is in fact, err, glass? And glass reinforced plastic most certainly fails in a brittle fashion. It certainly is not "tough" in the fashion that engineering metals are...

You sure about that? Fibreglass is really tough, it's not brittle like glass.
It's used in whitewater canoes, hammer handles, car bumpers, etc.
I once tried to snap a fibreglass fishing rod by bending it into a knot, then chomping it with the cutters on my pliers. When that failed, I put it across a kerbstone and stomped on it, then scraped it up and down the corner of a brick house - that didn't work either, it just sprung back to it's original straight shape . OTOH, my CF fishing rods crack across any sharp or blunt edges I accidentally put them across. If you don't consider fibreglass "tough", what do you make of CF?

...Carbon fibre has been used in aviation for over twenty years now...

Since the 1960's. But they'd rather you overlook the first 25 years.
A lot of CF "experience" has been gained with military aircraft, however I question how transferrable that knowledge is when it comes to civilian aircraft, which operate at a tempo 100X more intense, and spend 100X less time being inspected and overhauled.

...There is one crash that I can think of involving the failure of a carbon part - the failure of the tail section of an Airbus in the November 2001 New York crash. That was a result of inappropriate pilot repsonse to wake turbulence which overloaded the rudder. It broke when subjected to 2.7 times its maximum design load. Aviation experience demonstrates quite clearly that carbon fibre is perfectly safe with the correct design and fabrication...

But that's my point, the manufacturers still get CF design wrong with amazing frequency. Maybe their design tools and methodologies still aren't good enough when it comes to CF.
RR, Boeing, Airbus, Trek bikes, etc. are leaders in their respective markets with no shortage of engineering resources, and can still design CF parts wrong.

...The failure in the OP was at the point where the steerer tube is subjected to the maximum bending forces from the load applied to the handlebars. It was probably fatigue failure. Ironically the steerer would most likely not have failed had it been carbon fibre, as CF is much more resilent against fatigue than aluminium...

CF steerers crack, Al steerers fatigue and then snap, or just come unglued. Get a steel one .

 

[Oddsos]

Hi snailracer. I think the problem here could be discontect between engineering talk and the real world. Strong and tough are used in very specific contexts in engineering. Things can be very strong but have poor toughness. This is can be the case with carbon fibre or glass fibre reinforced composites. The material appears real world tough because it is very hard to break, however engineering toughness actually refers to how much energy is absorbed in the process of breaking. If the component breaks by snapping instead of bending it is probably not tough.

Most engineering metals are quite ductile. Once they reach the point that their strength is exceeded they continue to bend, absorbing more energy though plastic deformation. This is what engineers mean by toughness. Even very thin metal compenents that are not very strong (think aluminium cooking foil) can actually be tough!

 

[snailracer]

http://www-materials...s/NS6Chart.html

The above chart illustrates "engineering" toughness and strength.
Real-world toughness is, as Oddsos correctly pointed out, quite different, especially when it comes to bicycles.
For starters, frames made of different materials use different sizes and thickness of tubing, so simply comparing raw materials is misleading.
Also, the strength of brittle materials (CF, high-strength metals) are very much dependent on the presence or absence of flaws within them.
AFAICT, bike components are typically designed with the component load in mind i.e. strength - toughness appears to be an afterthought. I would therefore venture that real-world toughness of a material can be meaningfully measured by the ratio of toughness/strength.

If you zoom in on the "composites" region in the above diagram and consider that the axes are logarithmic, the diagram shows that fibreglass is much "tougher" than CF. The discrepancy in the ratio of toughness/strength is even greater. Bottom line - fibreglass is "real world" (AND "engineering") tougher than CF - but we all knew that anyway, riiiight?

For those interested, here's the zoomed region for metals:

 

[fossyant]

Boring ! ^

Obviously paranoid about the use of anything on a bike.

 

[mickle]

I fail to see what drawings of amoebas have to do with bicycles.

 

[feelfattergoinguphill]

funnily enough i was down at my lbs today where i got my giant tcx1 from. i was enquiring about the possibility of getting a set of alloy forks. i just don't seem to be able to settle down when riding with the carbon forks it came with, my reasons to be unsettled is that my scott genius ltd full carbon fibre mtb (£5000's worth) snapped in half due to a manufacturing fault (fracturing my eye socket and wrist and i was knocked unconscious for a short while). the frame was replaced by scott and the bike rebuilt by lbs, but i ebayed it.

the bloke at the lbs (craig at rideon in rossendale) is very knowledgeable and is involved in quite a few research and developments (bike related). rideon are giant dealers and craig goes to all the meetings a dealer has the opportunity to goto. he's been to a few where giant rep's talk about quality and prices and some others where they demonstrate the manufacturing process and quality control.

apparently not all cf is the same, i.e giant get the actual fibre's from the same place as boeing and f1 teams. in other words they get the best available, then they weave it in house and produce the components in house and keep a tight grip on quality. apparently giant have the ethos of it has to be 'fit for purpose' (which causes passionate arguments at dealer meetings, dealers want cheaper bikes to compete) and not built to compete with 'boutique' brands on lightness (eg, pinarello, colnago etc etc) the boutique companies buy in the already woven cf matting and 'swatch build' their frames with the ultimate goal being lightness and stiffness (fair enough, horses for courses).

giant actually build and have their bikes tested to some crash test standards (craig said EN summat or other) and are heavily involved with improving the standards of all bicycle frames and forks. craig says he really believes the company (giant) operate a show all policy and gets monthly emails regarding failures and recalls. he reckons in all the time he's been a dealer he's not heard (not even on the grapevine) about any problems with giant cf frames or forks.

now i'm not naive enough to believe everything i'm told by a dealer (obviously he may have an agenda) but craig seems to be a straight up guy and wouldn't sell cf mtb bikes until he started being a giant dealership.

what do you guys think? has he been straight with me (or giant straight with him).

i'm particularly happy with how he told me giant make their cf forks; a swaged end on an alloy steerer tube and then inserted into the machine that bonds the tube to cf & resin, i.e., not cold glued into a crown like a lot of companies used/do.

ribble bikes was one of the companies that was mentioned in the cheap chinese carbon category.

The rep was being a rep lol..... Giant use the exact same carbon fibre as you would find in a boardman or a ribble, Toray t700/t800 which is nothing special in the bike industry.From what I can gather by insiders out in the east(used too import carbon bike frames/bits)Giants reliability comes in its skill in the lay up(orientation of the fibres etc/resin properties etc)as standard FEA dosent work for carbon in the same way as metals.
Also ALL road bikes sold in the EU have to be tested to EN 14781 standard,its not just giant but all.(EN 14766 for mtb's)

Ribble's do buy from OEM for their latest frames the company is called Xspace and is one of the very best OEM's in bike industry who work directly with Toray, so same source for the carbon as giant(although xpa buy the pre-preg from toray as oppossed to giant who do their own)

 

[Scilly Suffolk]

Wood is the only material that gives you plenty of warning before collapsing. Bamboo? Not too sure yet.

Talking to an "old timer" (who stopped to admire my "steeler"), I was surprised to learn that, in the quest for lighter weight, they used to make wheels from bamboo.

He got his caught in tram tracks and it bent out of shape; in frustration he kicked it and it popped back into shape!

 

[mr Mag00]

these material threads are becoming like helmet threads

 

[Zoiders]

Next we know the OP will be warning against flying - all those dangerous weak Al and carbon fibre planes ought to be replaced with steel ones

Who are these mind-bogglingly ignorant people who go on about the 'strength' of a material as if it only comes in one - dangerous - form? I suggest they all move to wood bikes and avoid all technological materials as occasionally some component makes it past the QA test and fails in use. Humans being fallible, it's always going to happen

Unlike bikes the air frames of aircraft have a very well planned out service life in actual hours.

There have been warnings issued about the dangers of some countries that purchased airliners and never had them replaced or serviced properly by the manufacturer, leading to failure of the air frame and loss of life - so yes there are plenty of dangerous lumps of aluminium in the sky in various parts of the world.

The problem with ally and CF is not is lack of suitability it's the variability of the end use.

 

[snailracer]

these material threads are becoming like helmet threads

I'm tempted to start a thread about carbon fibre helmets with built-in headphones .