KonAaron Snake 

I know that riding style, weight, individual bikes, usage and other factors will alter the answer significantly, but I was wondering what kind of life span someone can truly expect from an aluminum or carbon frame. Are they over manufactured to the point where it's not really a relevant issue? Has anyone seen, or heard of, a frame dieing from pure fatigue factor (not an accident)?

The question also comes into play with wheels and parts...I think almost all of us are using aluminum or carbon rims...how long a life span do you get from them? Most of us are using aluminum or carbon parts...from handle bars to cranks. I'd assume that handle bars aren't really getting THAT much stress, but that cranks are probably under enormous pressure. Does anyone have an expectation on carbon crank life? I'd rather date it with an expiration date than find I reached that point on a nasty descent!

bigbossman 

Carbon Fiber does not fatigue. It spontaneously combusts.

rat fink

I don't believe the hype regarding aluminum fatigue in bike frames. While fatigue exists, I think it's safe to say that it has little application to bikes under normal (non abusive) conditions. I can see something like a crank eyelet be a concern, though. I suspect that also has more to do with impact though.

David Newton

I wasn't aware that carbon or aluminum were used in bike frames. Since when?

rat fink

Ha ha! True!

The thing that concerns me about CF is the failure mode: When aluminum fails, it fractures at it's weakest point. When CF fails, it fractures throughout. The reason for this lies in the elastic properties of the materials. CF has very little ductility, (the extent to which materials can be deformed without fracture. ...think bread dough), while aluminum features a fair amount ductility.

bigbossman 

When I bought my new aluminum Pinarello frame a couple of years back, the dealer that sold it to me made a point of telling me it had a service life of about 5 years of heavy riding. I asked him to define heavy, and he said about 10,000 miles a year. Most folks don't ride 50,000 miles in a lifetime, let alone 5 years.

I hedged my bet, though - I put about 2,000 miles on it and then sold it off to some sucker........

I still have my CF Giant. I love the way it rides, and have about 6,000 miles on it so far. Haven't ridden it much in the last 2 years though. Despite being a nice ride it just ain't as pretty as my Italian steel, and I like looking at them a lot more.

divineAndbright

Seems most aluminum frames come with a 5 year warranty, steel typically gets lifetime.. not sure about carbon but im sure its 5 years too.

I personally don't believe the whole aluminum shelf life or "good for XX miles" thing, look at all the cannondales and treks still kicking around since the late 80s/early 90s, not to mention all the aluminum components built since the 1960s and in some cases older.

Mike Mills

All things fatigue. Steel structures fatigue. Aluminum structures fatigue. Even graphite composite structures fatigue.

Fatigue life is usually dominated by flaws and flaw growth/propogation. Flaws are inherent in the materials and can also be induced during manufacturing and use.

Fatigue life must be dealt with statistically (Single samples are not statisically significant. It's like drawing a straight line through a single data point).

Good structural design anticipates flaws and is flaw-tolerant.

Fatigue life curves (cycles to failure as a function of strain level) are available for most common structural materials.

It is possible to estimate fatigue life using "cumulative damage" theory.

Mike Mills

Be careful with this statement. Some modern graphites have better strain allowables that are quite good. It is the high modulus graphites that have low strain allowables. Some aluminum alloys have very low strain allowables (are brittle).


P.S. - I think that crashing your bike is a legitimate loading case to look at. How the frame behaves when you crash may, in fact, be one of the most important load cases to look at. Crashes almost certainly result in structural failure (but not always). How your frame fails when overloaded like that is fairly important.

RobbieTunes

Around 1987, my friends and I used to "hill climb" a steep, 1/8 mile hill, losers pay for beers. I broke 2 aluminum Treks in 2 weeks, neither of them mine. LBS wouldn't sell me one after that. I'm not sure what would have happened if I'd put a carbon Ironman under the same stress, and I'm not sure I'd want to know.

I like aluminum just fine, and recently acquired a couple, both over 20 years old. We'll see, eh?

Carbon fiber is nice, but when you're riding the road, looking at the nice countryside, and then look down, it's still more satisfying, to me, to be looking down at a steel top tube....Just seems more...substantial.

bbattle

I hope the weather improves and people can get out and ride some more.

Carbon and aluminum frames, not wrecked, will last longer than you will. Same for steel frames. Ride what you like, don't worry about it.

Chombi

I guess I'm done for!!....
Maybe I should top the bike off with a pair of vintage wooden rims too!!...laced with CF spokes cross zero radial pattern front and back......and UV sensitive skinwall tires,.....and maybe a full CF saddle that will splinter apart on the smallest bump causing the accompanying CF seatpost to spear me at my nether regions...... I should really have a self destruct button on this bike to keep me from crashing in flames into old grandmas and boyscouts crossing the streets....when this all encompassing structural failure mode hits me on my first ride on the just finished bike!

Ehhh....... CF and aluminum....there's more "dangerous" stuff out there that we deal with everyday to worry about the stuff on our bikes too much.....

Chombi

thirdgenbird

great bike and great post

old's'cool

I'm not too well versed in carbon composite or composite structures in general regarding fatigue, so I'll refrain from comment on that, but I know they tend to be damage intolerant and fail catastrophically.
Aluminum and other metals I know a little more about. It is typical, in any field of design, that the more specialized and higher tech the application and resulting solution, the more precisely the design is engineered for the specified requirements, and hence the less margin there is for "off-design" conditions, whether they be loading beyond the maximum specified overload, or use beyond the intended design life.
This is very typical in aerospace, where critically stressed elements of an airframe or aero engine have not only fatigue inspection intervals, but also maximum lifetime either in operating hours or number of cycles, beyond which they are no longer technically nor legally airworthy. There is no reason this should be any different for truly high tech bicycle components. Putting it another way, if a structural component does not have a maximum design lifetime, then it is not really that high tech. Nothing wrong with that, and that's why we C&V people value the old steel frames so highly.

A little more on fatigue, which is one of the two focal points of this discussion. Mike Mills gave a very good introduction to the subject. The point I want to make about steel, is that unlike most other metals, it has a "fatigue limit" (a counter-intuitive name) which really means if it never gets stressed above ~20% of its yield strength, it will never suffer any "cumulative damage". Rephrasing this slightly, steel ONLY experiences cumulative damage when it is stressed above ~20% of it's yield strength. Other metals, notably aluminum, experience cumulative damage every time stress is applied and removed, regardless of how low the stress (of course the lower the stress, the lower the damage). That is, in a nutshell, why aluminum bike frames are known to crack in fatigue, and why aerospace structural components are condemned after reaching their designed number of operating hours or cycles.

The other focal point of this discussion is "toughness", which translates to how much damage (i.e. deformation) a structural element can sustain before failing catastrophically. Again, steel is far and away the winner over aluminum and composite structures (in general, there can be exceptions), in part because it is lower tech and has inherently more design margin.

slushlover2

I think I have owned all the popular frame materials. I have had steel, aluminum, carbon and titanium. Guess which is the only material I have ever broken (twice). I'll give you a hint. It was steel. I have had 2 steel bikes break at the juncture of the downtube and bottom bracket.
Does this mean I wouldn't ride steel? Of course not. I have a lifetime mileage nearing 100,000 miles. Most was on steel. You have to expect some failures.

TejanoTrackie 

All components that do not experience wear such as chains and brake blocks or environmental degradation such as gum rubber brake hoods and tires/tubes will last virtually indefinitely, provided they do not have any initial manufacturing flaws and are never loaded beyond their working stress. Steel can still corrode, as can aluminum, and bonding elements in composite construction can still degrade. However, generally speaking, a properly maintained and not abused component will last for decades. I have numerous steel frames that are over 25 years old, and show absolutely no sign of failure. I can't speak for aluminum and carbon, as I have few of those and they are not particularly old, however, I see no reason why their lifespan should not also be many decades. Of course, there is always titanium, but the very high cost has always been a barrier for me.

Road Fan

I think it needs a set of integral crutches to help handle those inevitable fatigue failures you're sure to have. They'll need to be wood, of course.

bikingshearer 

The first and second ones you own do. The third one catches fire. falls over and sinks into the swamp.

91MF

barring corrosion, aluminum only 'ages' with stress/pressure. if you dont ride it, nothing is happening.

prathmann

I've also had two steel frames fail. Meanwhile, my only Al frame is still doing fine after more than 100 kmiles - substantially more than either of the steel frames had. OTOH, both steel frames were repaired and I still have (and use) those bikes as well.

jgedwa

Blessed are the cheesemakers

Chombi

Nahhhhhh........ why not live really dangerously and make them out of chocolate and licorice instead??

Chombi

bigbossman 

Oh, what sad times are these when passing ruffians can say `nee'
at will to old ladies.

Road Fan

I thought fatigue life was based on the size of stress/strain cycles relative to the elastic range of the material, and the number of stress/strain cycles. If this isn't the case, how can a cumulative damage theory be used?

Failures due to fatigue begin at places where there is a microcrack, inclusion, or other flaw where stress is concentrated during normal use and stress cycling.

Road Fan

Great idea! Ride food!