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the wrench
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materials like steel and ti are said to have an infinite fatigue life compared to al. steel and ti will just take many many many more cycles than al that for its intended use its almost infinite.
 

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garboui said:
materials like steel and ti are said to have an infinite fatigue life compared to al. steel and ti will just take many many many more cycles than al that for its intended use its almost infinite.
ic....so if generally Aluminum vs Carbon..which one has longer fatigue life?
 

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I don't have any experience with carbon frames, but I DO have experience with carbon handlebars. I ended up snapping my Eastons near the shifter on the right side.

I know carbon is exceptionally strong, but if the performance of a carbon frame is anything near what I experienced with my handlebars, I would say WATCH OUT!!! When carbon fails, it REALLY FAILS...like snapping in 2 very quickly with no indications of cracks. I've had one Al frame that cracked, and I found the crack before the frame split in 2. With the carbon bars, they just violently snapped in 2 with no warning, which caused one of my worst crashes.
 

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mafia6 said:
ic....so if generally Aluminum vs Carbon..which one has longer fatigue life?
With all the above, Ti, Carbon, Al, Steel, Unobtainium - it depends on the design.

All materials can fatigue, and quickly, if designed poorly. They all can also be overbuilt to the point where they effectively have an almost infinite fatigue life. For frames that are pretty comparable - all lightweight XC bikes - a Ti or Steel bike should have a longer fatigue life than Aluminum, but a carbon bike could fall at either end of the spectrum depending more on impact resistance.

JmZ
 
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mafia6 said:
wow thx u guys are great.. :D
If you mean mostly wrong then yeah......... they are great.

Fatigue is a failure method in which a small crack starts in a part from being repeatedly loaded at a stress level that is much less than the ultimate strength of a material. The crack propigates with each stress "cycle". Steel and titanium can have an unlimited fatigue life, but it depends on the individual design. Aluminum has a finite fatigue life, no matter the part, and no matter the load. Meaning if you repeatedly stress an aluminum part it will eventually break.

Carbon simply doesn't suffer from fatigue in the traditional sense, it has an unlimited fatigue life regardless of design.
 

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Hosehead said:
If you mean mostly wrong then yeah......... they are great.

Fatigue is a failure method in which a small crack starts in a part from being repeatedly loaded at a stress level that is much less than the ultimate strength of a material. The crack propigates with each stress "cycle". Steel and titanium can have an unlimited fatigue life, but it depends on the individual design. Aluminum has a finite fatigue life, no matter the part, and no matter the load. Meaning if you repeatedly stress an aluminum part it will eventually break.

Carbon simply doesn't suffer from fatigue in the traditional sense, it has an unlimited fatigue life regardless of design.
I'm not an engineer but isn't fatigue a failure that starts on the molekule level? Meaning that over time the properties of a material change?
 

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Elitest thrill junkie
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There's also something called the "fatigue limit". If this is exceeded you throw everything out the window and you are in uncharted territory as far as when or if the bike will fail. Everything has a fatigue limit, and there may not be any indicator to let you know that you've exceeded the limit.
 

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carl1266 said:
I'm not an engineer but isn't fatigue a failure that starts on the molekule level? Meaning that over time the properties of a material change?
Properties of some materials can change over time, but that is a completely different phenomenon from fatigue.
 

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Gravity Rides Everything
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damion said:
Any material can fail from fatigue.
steel, and I THINIK titanium have an infinite fatigue life. this is of course assuming that you keep the load under a certain amount.

carbon is kind of wacky when it comes to fatigue. I do know that impacts above it's normal working strength basically destroy it though. it's definitely not as forgiving in that sense as metal.
 

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Jayem said:
There's also something called the "fatigue limit". If this is exceeded you throw everything out the window and you are in uncharted territory as far as when or if the bike will fail. Everything has a fatigue limit, and there may not be any indicator to let you know that you've exceeded the limit.
The fatigue limit is simply when you have undergone enough load cycles at the proper load that you can then expect a fatigue crack. Everything does not have a fatigue limit. For example a carbon fiber part doesn't fatigue, so it can't have a fatigue limit.
 

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Gravity Rides Everything
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Hosehead said:
If you mean mostly wrong then yeah......... they are great.

Fatigue is a failure method in which a small crack starts in a part from being repeatedly loaded at a stress level that is much less than the ultimate strength of a material. The crack propigates with each stress "cycle". Steel and titanium can have an unlimited fatigue life, but it depends on the individual design. Aluminum has a finite fatigue life, no matter the part, and no matter the load. Meaning if you repeatedly stress an aluminum part it will eventually break.

Carbon simply doesn't suffer from fatigue in the traditional sense, it has an unlimited fatigue life regardless of design.
i think fatigue has more to do with work hardening than an actual crack.
 

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Elitest thrill junkie
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Hosehead said:
The fatigue limit is simply when you have undergone enough load cycles at the proper load that you can then expect a fatigue crack. Everything does not have a fatigue limit. For example a carbon fiber part doesn't fatigue, so it can't have a fatigue limit.
No, for those materials that do not have a fatigue limit, the limit is the maximum load they can bear before the integrity is compramised.
 

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Hosehead said:
Right, single cycle fatigue failures are common. :D
Depends on the load imposed.

We can do irreversable damage to our planes real fast by exceeding the LLF, but the wings should stay attached long enough to get back on the ground. Exceed the ULF, and they may rip right off.
 
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