AnthonyG

This topic always gets people going and I don't really want to keep it going but I feel the need to clarify one important point. 50 tooth Cannon wrote "shelf life" in the title but proceeded to talk about the frames life in USE.

2 completely different issues. If you left an aluminium frame on the "shelf" and didn't use it then as long as its was stored correctly and didn't corrode then its not going to "expire" from sitting on the shelf. As clylodan pointed out, we are really talking about FATIGUE life and yes, aluminium does have a fatigue life as opposed to steel which doesn't have a fatigue life/limit.

What this means in practice is up for much debate but lets get what we are talking about straight.

Anthony

tcs

Uh - what's magic/special/different about using aluminum for frames, as opposed to using aluminum for stems, bars, posts, cranks, rims, nipples and hubs?

tcs

AnthonyG

Wall thickness. Its when you try to exploit aluminums lightweight properties to the maximum possible that you run into fatigue life/limits. Mind you there have been a few examples of aluminium crank failure around here recently.

Anthony

tcs

And no one has ever used aluminum to build the lightest possible stem, bars, rim, hubs, cranks...?

tcs

AnthonyG

Yes they have. And they break.

So where were we.

Anthony

bumperm

The real problem with aluminum is that it can spontaneously combust. Given enough time and moisture within the frame from condensation, the aluminum will turn to aluminum oxide. And everyone knows that aluminum oxide, in the presence of enough carbon dioxide, will combust or even explode! And with the CO level in our world is increasing day by day, it's only a matter of time before aluminum bikes start going off with little or no warning - BANG! Best not ride near one, let alone on one. Being hurled through the air near the finish line is no way to win a race.

bumper
aluminum is temporary, steel is unreal, carbon like diamonds is forever

JanMM

Hurled straight ahead might win the race!

HillRider

If the CO level is increasing, none of us will have to worry about frame life. We'll all be dead way before that's a problem.

conspiratemus

Not so far-fetched. Even hurled straight up might help. I remember a photo of the wreck of a CF-104 jet fighter whose engine had flamed out just after take-off. Because of its stubby wings, a 104 would drop out of the sky if its afterburning turbojet stopped doing the pushing. The photo shows the ejector seat lying on the runway several dozen yards beyond where the airplane came to rest. (Fortunately the pilot had separated from the seat and parachuted safely.) The crash investigators noted with some amusement that a chair would glide farther than an airplane. Not for nothing did the RCAF guys call it The Lawn Dart.

Rollfast

Well, then! This fully explains the Chevy Vega.

You do recall I own a 50s Rollfast cruiser and early-mid 60s Western Flyer and that at 278 lbs I really need more credit for carbon so I'm still with steel.

PS I'm not that cute, honest, thank you though.

mud

All frames should come with a "Born on date." just like beer.

HillRider

They do. The serial number will get that information for you.

MadMabel

I've been following this thread with a great deal of interest as I am in the process of building up a 1989 aluminum Paramount 564 frame.

The frame came from eBay and I have no idea of its history. Since the bottom bracket and headset were shot (the headset cups were badly brinneled) I am guessing that it has not had a gentle history.

Do you think that its worth building with good components? Shimano 105, mostly. Or do you think that it would be better to look for another frame?

FWIW this bike seems to have a reputation for being very stiff and giving a harsh ride. I am in my 60's and not as flexible or resilient as when younger. But I do have this frame now and money is tighter than could be hoped.

Mr. Underbridge

That's from exceeding the stress tolerance of the part, not from fatigue. Those are completely, totally different things. You can break a new part if you subject it to enough stress.

A question to those who think that frames should be retired - are we talking about the joints cracking, or the tubes failing? I'd me much more worried about the joints cracking than a tube failing. Compare bikes to other structural applications of aluminum. The pittance of ride time experienced by an aluminum frame is nothing compared to rigid members in an airplane, which can see near constant use for decades without being retired.

Now, if you're talking joints...well, that's why structures exposed to heavy loads aren't welded. But cracked joints can happen to modern frames too. At some point, you have to accept the fact that parts on your bike can fail. One solution is to actually wash your bike so you're more likely to see little cracks. Also track down mystery noises that might be coming from a cracked joint.

But if the OP has a light, high-quality vintage aluminum frame with low miles that he just doesn't feel right riding or selling after reading this thread...send it to me, I'll cover postage.

noglider 

A few years ago, Cannondale had a deal where, if your Cannondale frame broke, they'd replace it. That was because they can't be repaired, and they were competing with steel frames that can be repaired. Not only that, aluminum was known to fail in worse ways than steel, because the failure is more sudden and more likely to cause injury. This was at the time when aluminum frames were less common and had to overcome people's fears of them.

I don't know if Cannondale offers this deal any more.

Bike shops do their part to promulgate the folklore, which is often wrong. There was the concept that a steel frame gets less stiff over time. The bike people called it "whipped." I had a LBS owner tell me my frame was old enough that it must be whipped. Tell this to a metalurgist if you want to supply him with uproarious laughter.

I don't know about the fatigue qualities of an aluminum frame, but I haven't heard any horror stories, so I'd say that the advice above is good: inspect it every once in a while. As long as it doesn't develop any cracks, you're probably safe.

And yes, the terms "shelf life" and "half life" have been misused here, but the question behind the misuse is still a fair one. As far as I can tell, normal use of an aluminum frame will result in many years of service, so many that we don't yet know how long we can expect them to last.

crocodilefundy

aluminum is subject to fatigue more so than steel. there is an exponential relationship between the amount of force applied and the number of cycles before failure. ie. the max load is one cycle. if you let the frame sit there it will never fail due to no load being applied. there is also an endurance limit which is a limit in loading where fatigue starts to occur. I'd guess that a normal aluminum frame is probably over the endurance limit but the number of cycles to fatigue can be like ~10^9 or more.

In general the frames probably will fatigue, i know i had a cross bike from 1999 that failed due to fatigue in the bottom bracket area. however that was caused by 9 years of a 200+ lb person abusing the bike every day in all weather.

just keep riding your bike until it begins to crack then replace it.

Little-Acorn

Aluminum pop cans dumped in landfills, are said to be still shiny-new a hundred years later.

Maybe if you want your bike to last, you should bury it....??

jhota

just to be a pedant, steel does fatigue.* just not as quickly as aluminium.

and fatigue life is affected by many things; specific alloy type, surface preparation, manufacturing stresses, etc.

i think that aluminum frames got a bad rap because of failures due to manufacturing stresses in the early days - when the industry started moving from lugged/brazed/welded steel to welded aluminium, there was a learning curve. aluminium can be much affected by overheating during welding. it's also more sensitive to atmospheric issues (too much oxygen or nitrogen) when welding than steel. you take framebuilders who are used to steel (welding or brazing), and have them start building frames from aluminum, it will take a while to build proficiency.

*for a well-known historic record attributable to a steel fatigue failure, google "Great Molasses Flood."

noglider 

Yes, all things being equal, I'm sure the steel frame is safer and more durable. Steel has a much bigger margin of error. But aluminum frames have improved a lot in recent years, and I would trust one. When they came out, I wouldn't.

gbg

I have a 87 (or 89 can't remember for sure, so it's about 20 years old) Rocky Mountain Stratos frame. The first aluminum MTB frame Rocky Mountain built if memory serves me correctly. It is bare aluminum so it shines up just like chrome when I have the motivation to polish it for an hour or so. It is now my commuter/winter bike so it gets pretty well abused. I have ridden in up to -35C. Haven't seen any signs of fatigue so far (no funny sounds, and I inspect the frame every so often). Oh yeah, it has endured my lighest 220lbs and heaviest 275lbs with no complaints so far, and I think it will for many more years.

HillRider

Continuing is the pedantic mode, steel does have a finiter fatigue life IF the repetative stress is above a threshold value which is thpically about 50% of its yield strength. Below that value steel has an infinite fatigue life. So, if you keep the stresses low, steel will theoretically last forever.

Ti, at least the better alloys like 3Al/2.5V and 6Al/4V, shares this property of having an infinite fatigue life if the stress levels are below the threshold.

On the contrary, Aluminum has a finite fatigue life even at low stress level. The lower the stress, the longer it will last but there is no "infinite life" threshold.

noglider 

Right, it's not infinite, but for most practical purposes, it's very long.

DiabloScott

Let's back up here. Fatigue is a failure caused by a small crack that gets bigger because of cyclical or repeated forces. Fatigue can happen in any of the common materials used to make bicycle frames under even very small loads once the initial crack has appeared. And once the crack has started, it becomes meaningless to discuss the fatigue limit of the material.

That initial crack can be a pre-existing flaw, damage from welding, damage from a tool, damage from a crash, damage from tightening a clamp too tight... any number of reasons. In the case of undamaged steel, if you keep the loads below the "fatigue limit" then the crack won't just appear no matter how many cycles you put it through. In the case of undamaged aluminum, with enough cycles of stress eventually the initial crack will just appear at some point no matter how low the loads are. But those are laboratory test samples like a simple tube or billet, not fabricated frames or components.

I have seen quite a few frames and components that failed in fatigue and every single one of them had some kind of damage or flaw that started the crack, - even frames that were purposefully destroyed in a fatigue test failed at welds or drillings or braze ons: LINK

So the real reason why it's pointless to discuss the fatigue properties of frame materials, is because the fatigue property of the material is not the cause of the fatigue of the component - it's the quality of the construction and the existence of damage, and the crack can get started from something as small as an engraving or machining mark.

Pocko

The OP asked about shelf life, so technically the issue is not metal fatigue but rather the issue pertains to heat treatment of aluminum. If anybody really want to leave all this conjecture behind, you need to ask a qualified metallurgist who is experienced and specializes in aluminum heat treatment. Opinions from anyone else is, well... an opinion.

The two most common aluminum alloys used in bicycle frame production are 6061 and 7005. They begin as zero state and somewhere along the line are heat treated. The correct question to ask is "does the heat treatment of these specific alloys "self-anneal" over time when these materials are left alone in storage?"

.

Rollfast

Because we use the bikes to kill off the beer?