CliffordK

Aluminum, steel, and titanium will all develop stress and fatigue cracks.

I've seen frames and photos of frames with cracks. I presume they develop slowly over time so rapid failure would be rare as long as a rider pays attention to the bike, but perhaps they could worsen quickly enough that a person might have to walk the second half of a century ride.

CF MTBs are apparently quite resistant to fatigue.

I've seen photos of cracks developing in CF road bikes, although there is some debate on the depth of crack or whether they are primarily in the paint. Material interfaces such as crown/blade attachment points for forks would be a potential place for CF cracks to develop.

Scooper

Alias 530 asked an honest question asking about advantages of titanium an steel over carbon fiber in a thread titled "titanium vs. steel", and I offered my opinion based on the physical properties of the materials. Please explain these failures if not because of "applied deflection or strain":









The warnings about carbon fiber failure mode are prominent in most manufacturers' literature; for example, these are warnings by Trek to buyers of CF bikes:

benlees

If they made CF bikes that looked like a Colnago C40/C50 today without the Colnago name tax, then I would consider it. What I mean, of course, is a nice horizontal top tube without the massive tubes. Mainly, aesthetics. Otherwise, it's older steel or titanium, which can be had for a song used, that satisfy. Threaded bb is nice too! Titanium wins strictly on day to day: no rust, no "Not my colour!", can lean against a lamp pole without scratches, etc. If you are lazy, absentminded, and hard on equipment (like I am), then titanium is truly worthy.

D1andonlyDman

That's a poor semantic argument. The fork is part of the frame - the part that the front wheels and the stem attach to. The fact that aluminum is not well suited to make forks means that the part of the frame to which the front wheels attach, and which fundamentally impacts the comfort and handling of the bike, will generally be built with something else besides aluminum. It is only a result of the fact that aluminum is not well suited to make forks, that the fork has ever become a discrete component from the main diamond of the frame itself. Back in the day that steel was the dominant frame material, all frames came with forks that were made from the same stuff that the rest of the frame was made with.

Scooper

Survivability.

Metallurgy for Cyclists - Carbon Fiber Boasts Tremendous Potential | Scot Nicol

D1andonlyDman

Yes, the Y-Foil is a road bike that Trek originally developed for Lance to do time trials with in 1998. The fact that it was banned in 1999 by the ICF due to politics to protect small European bicycle manufacturers (At the time, it required a large capital budget to build a CF monocoque frame - whereas nowadays that task can be and usually is contracted out to one of several Chinese factories) does not in any way diminish my enjoyment of the bike as a recreational rider - arguably, it made a used Y-Foil more accessible to someone like me for a good price. Also, even today, 16 years after Trek ceased to make them, Y-Foils are competitively used in triathlons (which are not under the auspices of the ICF). And yes, the shape of the carbon monocoque frame of the Y-foil does a great job of damping out vibration of bumps, without degrading the lateral stiffness and energy transfer to the pedals, as the rear wheel is entirely de-coupled from the rider's seat

halfspeed

Any crash serious enough to asplode a carbon frame is going to do some serious damage to any frame of any other material, not to mention the rider.


Emphasis added for the significant point.

halfspeed

Not it isn't. It's the fork.

Back in the day, steel was the only material so there wasn't anything else that could be used for a fork. Even then, forks were often a different steel alloy than the frame.

rpenmanparker 

I imagine the reasons for those failures are very similar to the reasons for nearly identical looking failures in steel, aluminum, and titanium.

By the way, one other point. The tensile and flexural ductility of materials is determined for standard purposes at very slow speeds such as an increase in deflection of 0.5-2.0 mm/min. Under those conditions yes, you may get up to 15% elongation in steel before catastrophic failure, although the yield point after which the material is essentially ruined will occur much earlier. But a crash occurs at a much, much faster speed so that the resistance to breakage of any frame in a crash is governed by its properties related to resistance to impact. The faster the application of the stress, the shorter will be the elongation to yield and break, temperature being held constant. Just a guess, but I doubt that steel exhibits anything even close to 15% elongation at break in an impact situation.

rpenmanparker 

Who cares about semantics. It is a great functional argument.

D1andonlyDman

Nope - the frame is the part of the bike that holds the wheels. The fork is part of the frame, because you can't attach the front wheel without it.

Try using a frame without a fork. You can't.

And aluminum makes a crappy material for that part of the frame.

Claiming that the fork is not part of the frame is like claiming that the hub is not part of the wheel.

Scooper

There's always a tradeoff between the added material to build in "a big safety net" and weight savings, but adding material doesn't alter the failure mode.

Scooper

Both forks have failed as a result of collision impact at speed.

You are welcome to be on the bike with the carbon fork; I'll take the steel one. We'll see which of us escapes with less serious injuries. Caveat emptor.

rpenmanparker 

You can disapprove from now until eternity, but the standard nomenclature that has evolved to this time is the double diamond frame is the frame and the fork is the fork. That is just the way it is.

D1andonlyDman

Well then it's evolved to the point that it's become inaccurate. And in any case, Aluminum is not vertically compliant enough to make suitable forks. Which is why it's an inferior frame/fork material, compared to all of the others despite it's light weight and stiffness. And if it makes you more comfortable, I'll simply refer to them as frame/fork material from now on. And BTW, not all frame/forks are double diamond (for example, my Trek Y-Foil), so how does your nomenclature deal with that without being explicitly inaccurate?

dnslater

Can't use the frame without wheels, also.

D1andonlyDman

Which is why the frame/fork is the part of the bike upon which you hang the wheels. So you can use it.

halfspeed

You're making up your own definitions to support a specious argument. You aren't fooling anyone except, perhaps, yourself.

rpenmanparker 

I don't often give up on somebody ever getting it, but I'm done. Let's see where we are leaving this: because aluminum is not ideal for a fork, then it shouldn't be used for the frame either. Tell that to every major bike manufacturer.

D1andonlyDman

As I said, Aluminum makes an inferior frame/fork material because it can't be made vertically compliant without subjecting it to fatigue. That's not fooling anyone, it's simply fact. And whether or not you consider the fork to be not part of the frame does not alter that fact, and aluminum remains a lesser material than either steel, titanium, or carbon fiber for the frame/fork.

Good. Nobody would benefit from my accepting your inaccurate nomenclature. And I certainly couldn't care less if you give up on my ever acquiescing to your inaccurate nomenclature, even if it's widespread. But just for you, I will be using the term frame/fork from now forward. And even you recognize that aluminum makes a LOUSY material for constructing the frame/fork.

rpenmanparker 

So why is it so successful as a frame material then?

D1andonlyDman

Because it's cheap. But not particularly good, as it makes lousy frame/forks, forcing manufacturers to make their frame/forks with multiple materials. And nowadays, it's only used on the frame/forks of low end bikes.

RJM

It's cheap and lighter than steel.

dr_lha

I'm glad this thread about Titanium vs Steel has now moved onto "CF assplodes" and "Aluminum is crap".

rpenmanparker 

Rhetorical question!