What broke? Carbon or Alu? - Page 2

OK, I see Alpha-Q had one also - don't appear to make it any more and it doesn't appear to have any advantage over steel or aluminum though, and is more susceptible to fatigue - BUT ONLY AFTER A CRACK STARTS which might be the case after a crash.

Ti steerers are much harder to cut down, that's probably why they're so rare.

Additionally, the titanium steerer option on the Kestrel fork was more than $200US MORE than one of their "regular" carbon fiber forks ... something like $450US, 5+ years ago, comes to mind.

FWIW. The only way I know how to "cut" a titanium steerer is with a hand grinder ... there is probably a more elegant way to do it.

Okay, I agree with most of what you say. Especially about not fearing aluminum! I agree that fatigue failures can start with an incipient crack. However, fatigue failures have another known mode. Weak spots inside and inherent to the material such as an inclusion, impurity or other irregularity are known nucleation points for fatigue cracks. The crack grows from that point until it breaks. This is why all metallic structures have a well defined fatigue life.

Aluminum can be a bit worse than other materials, but this can be counteracted with good design. Generally, metallic fork steerers should have at least an order of magnitude more fatigue life than your chain stays because of the immense wall thicknesses.

The big question mark is carbon. It's fatigue modes are undefined, since there are no grain irregularities, impurities, etc. And when there are inclusions or voids, the cracks only propogate until the next layer where they stop (isotropic materials do this at boundaries). Carbon fiber hasn't been around long enough for engineers to know what it's typical lifetime is under a known load. It's obviously a long time, but it's undefined right now. At least that's the last I heard on the subject. Experts might disagree.

John Swanson
www.bikephysics.com

I think you’re the one full of BS.

Just look at your post, its full of negativity.. And your previous one? Trying to arouse sympathy and get everyone to gang up on whoever disagrees with you? Then you accuse me of trying to scare everyone off aluminum? BS ain't it.

Instead why don’t you open up your narrow mind, read my posts again and really see the wisdom of it. If you cant, let me spell it out for you like a five year old. ----> Any one using an aluminum steerer for sometime should examine theirs to avoid such failures, specially more so if involved in a crash. I am not against using an aluminum steerer.. I've used one for years (till it broke because I didn’t examine it whenever I serviced the headset).

And one more question for you Diablo... Hincapie crashed, and what broke? Yes an aluminum steerer!!! (he could have broke the carbon legs of his fork or the carbon top tube or the carbon downtube or the carbon chainstay or the carbon ... whatever).

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Talk about being full of BS: you've presented zero science or deductive logic, but you have brought a lot of invective. You should take some engineering or science classes, so you can learn some science, reasoning, and empirical thought.

Are you talking about yourself? OIC your diablo's lover right?!!!

Maybe you should stop riding with just your seatpost. A seat would be more comfortable specially with that aero post.

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Ditto for carbon fiber... in fact manufacturers usually include such a caveat with their carbon fiber components.

I thought the Trek bikes used in Paris-Roubaix were Madone main triangle with Pilot rear triangle and fork.

I think the fatigue will have started long befor the crack appears, i still can't believe anyone would use an aluminium steerer on a cobbled race. seems nuts to me. Iv crashed head on into a car befor with a full chromo fork and that didn't snap it just bent all the way back and put a nice hole in my shin.

Seems obvious to me who's full of bull. aluminium is not a strong material it never will be and no matter how many times you say it is that wont change. we use it because it has an acceptable strength for the application. obviously some carbon fiber methods are stronger as is chromo and ti. and befor you call me a bs artist. I know this as fact because iv stood in a damn lab for weeks on end testing the damn stuff.

NO! The very definition of fatigue requires an initial crack. The crack can come from damage, a material flaw, or cyclical stresses but it always starts as a crack.

Thousands of racers on hundreds of cobbled races and ONE breaks AFTER it already was damaged in a crash... seems like a good history to me.

That's not fatigue. Al, steel, and CF would probably all have reacted differently to your crash. The stresses there would probably have sheered a carbon fiber fork right off.

It's the design and construction that matters. Absolutes based on bulk material properties are useless because, lo and behold, materials are used in "applications".

Your argument is laughable and getting rediculous all the time.

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Same as diablo... you bunch of novices are trying too hard on your case... just useless banter.

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Close, but I disagree on some major points. http://en.wikipedia.org/wiki/Fatigue_%28material%29 is a good place to start. What fatigue requires is an initial nucleation site, not a crack. Some materials such as aluminum intrisically have nucleation sites at the microscopic level. Others such as titanium and steel have very few nucleation sites, hence an apparent infinite fatigue life below a certain threshhold. However, all bets are off if the part is constructed with an inherent point of stress concentration (stress riser).

Typical stress risers in a steel frame are rust spots. Other stress risers are drilled parts - things like water bottle bosses. Chain stays usually do not stay below the infinite fatigue life stress limit and will eventually fail regardless of material.

Cyclical stresses are what cause the nucleation site to grow as the localized stresses exceed the material limit. They do not cause the crack. They cause the crack to grow from their microscopic level.

DiabloScott, it sounds like you have a lot of knowledge to offer in this debate, but your tone and confrontational manner are turning people off. It makes people defensive and they stop listening. Not that the rest of the people in this thread are doing much better...

<edit> HD_Reynolds is actually being the offensive one in this thread. Let's keep the rhetoric down and talk facts. BTW, I think bulk material properties are the whole point of this conversation </edit>

John Swanson
www.bikephysics.com