If a Aluminium frame sat on a shelf for 2 years does it start to fatigue immediately. The warranties offered with AL frame sets appear to be in the region of 5 years so if you bought an 03 model whilst the warranty would apply for 5 years, the manufacturer would have offered it with the intention of it being 5 years from 03 not from say 05. The question is, does an AL frame set start to fatigue / deteriorate from the date of Manufacture even if it has never been assembled or ridden? Does the same apply to steel?
Steel doesn’t fatigue, which is why it’s not uncommon to get lifetime warranty on steel frames.
Same applies to Titanium and Carbon Fiber.
The fatigue life is in reference to repeated stresses. So if it just sits there then there is no stress unless the frame was welded incorrectly. This is just a rough figure probably based on testing a frame in a rig a known number of times and comparing how long a frame lasts in the test to the real world and then adding a margin of error. Ti and steel will not fatigue but if you bend it more than it likes it breaks. Folks know that aluminum will wear out but they don’t want to go broke replacing them. Having said that, most people can get much more than five years out of an aluminum bike. On the other hand, many people don’t keep a bike for five years. On top of that, the manufacturer’s warranty usually only applies to the original purchasers with some exceptions out there.
The short answer to your question is no the aluminium frame will not fatigue while sitting on the shelf.
The whole area of frame failure/fatigue is extremely poorly understood by most cyclists/triathletes who would generally rather cling to old wives tales and rumours than engineering fact or science.
Ignoring carbon frames …which I would rather leave people with more knowledge to comment on.
Metallic bike frames (steal, aluminium, titanium etc) generally fail by one of two methods.
The JRA method…“I was just riding along and my frame just crumpled”.
This translates to “I was tearing down the road not looking where I was going and ran into the back of a parked car. Any chance your enough of a sucker to give me a warranty” …simple answer no…complicated answer…no!
The other main way in which frames fail is fatigue cracks… this is where a good warranty might help.
What happens here is a frame has a small defect , might be a small nick in a tube, a design fault, poor welding, heat effected metal etc, etc.
This fault causes a “stress riser” or high stress point, over time (under load e.g. riding) this develops into a crack which eventually leads to aframe failure. Itdosen’t matter wahat metal the bike is made of…and I repeat IT DOESN’T MATTER WHAT MATERIAL THE BIKE IS MADE OF!!! if there is a significant enough “stress riser” and the bike is used enough it will fail.
Poorly designed and built bikes which are ridden a lot fail. The material isn’t a significant factor in the equation. Frame fatigue testing has proven aluminium, carbon, titunium and steal can all produce great long lasting bikes and no material is a clear winner or loser.
And as for stories of frames going soft…I am yet to see any evidence to support this in mettallic frames…it is however a great way to convince your wife/ partner that you “NEED” a new bike.
Unless the area in which the al bike is stored has lots of corrosion potential (and the bike is not properly protected against it), fatigue will only start when putting loads onto it, and will probably take many cycles before it is a broken frame. You could take that aluminium bike, put it into a time capsule, open the capsule fifty years later, and probably ride it (provided that you can find drivetrain parts to fit it, as well).
Wilfried,
If steel doesn’t fatigue, how does it fail then? Surely you’ve broken steel frames? Titanium also fatigues. They don’t have the same curves in terms of load/time to failure, but any metal based material subjected to a high enough load over time will fail. From my time in the industry I’ve seen plenty of broken aluminum frames, but there is a make of titanium bikes that would routinely fail at the “bulleted” end of the chainstays at the rear right side drop out. Material isn’t a cover for poor design.
-SD
Sorry I haven’t broken steel frames.
From http://www2.sjsu.edu/orgs/asmtms/artcle/articl.htm :
Ferrous alloys (a.k.a. steel) and titanium have a threshold below which a repeating load may be applied an infinite number of times without causing failure. This is called the fatigue limit, or endurance limit. Aluminum and magnesium don’t exhibit an endurance limit, meaning that even with a miniscule load, they will eventually fail after enough load cycles.
related question.
how long does an aluminum frame last? i have a 1999 cannondale ms 2000. at what point do i start to worry that the frame might fail, not from a crash, but from fatigue or other factors?
I have not broken any steel frames,but i have repaired a bunch, i have broken three Aluminum frames and have four Aluminum frames right now,and will ride Aluminum in the future,everything breaks,just give it time
.
That threshold is well below the stresses that a bicycle endures in it’s lifetime.
If you tap your finger on an I-beam, it will never fail. Your comment on the endurance limit was not mentioned before, you only stated that the material does not fatigue.
-sd
Well, he is right. Steel and titanium do not fatigue (as defined by repeated stresses below the failure point), not ever. A properly designed and maintained steel or titanium frame will never fail from fatigue.
Here are the rec.bicycles FAQ entries on the subject:
http://draco.acs.uci.edu/rbfaq/FAQ/8e.4.html
and
This is a very silly discussion
You are trying to apply limits based on material properties (fatigue limits) that are really only applicable to a single (uniform) piece of the material that is repeatedly stressed
When you have a complex structure such as a bicycle that is made up of parts bonded (welded) together, intricate shapes, and various detailing and machine work applied to the structure you cannot make such a generalization. I would venture that most of the time, when a frame breaks (and it wasnt in a crash), it breaks at
a) a stress riser caused by either a dent, poor machining/finishing
b) weld (stress riser) or weld area (excessive heating which can adversely affect the heat treatment)
That is why many companies such as Storck, cannondale, cervelo, and klein have smooth welds - they are attempting to remove any potential stress risers. Granted some methods are better than others…
You only have to look at the EFBe results to see that many well designed aluminum frames will last a long long time compared to ti, steel and even carbon frames.
Bottom line: Bicycle frame fatigue life depends on many factors including design and manufacturing and is not as simple as choosing a frame material
Those interested may want to take a read at the articles I’ve linked to below:
I just read both FAQ’a and I fail to see where it say’s “A properly designed and maintained steel or titanium frame will never fail from fatigue.”
The closest I see is this statement “The big difference between steel and aluminum as a material for bicycles or anything similar is that you can design the tubes in a steel frame so that they will NEVER fail in fatigue.”
Notice especially the line “…is that you CAN design…” I don’t think this means that steel bikes ARE designed to never fail. In fact I suspect a steel bike designed to never fail would not be one you’d want to ride…particularlly up a hill.
No doubt Steel, TI, carbon etc has a longer fatigue life than aluminum but I doubt steel bikes are design for infinite life.
~Matt
stresses encoutered while USING a bike exceed the minimal force at which the frame will cycle forever.
I know that an ant walking on an airplane wing will eventually break it, it is made of aluminum and it has an endurance limit. We won’t see it happen however because of the load being so small. The load is not small on a 4 pound steel bike frame.
-SD
I don’t believe that the forces exceed the fatigue limit. If it did, you’d get plastic deformation (read: permanent, measurable damage) of the metal. Either it is below that limit, and it can cycle forever, or it exceeds that limit and deformation occurs. Are you saying that isn’t the case?
Note that I’m not a metallurgist, but I’ve read what they say, and that is my understanding.
“Are you saying that isn’t the case?”
That is not the case.
My understanding is that you have three points.
A point at which the material bends and does not return to it’s original shape.
A point at which it bends and does but is above “fatigue limit”, in other words the material accrues fatigue.
A point at which it bends and is below “Fatigue limit”, or does not accrue fatigue.
Aluminum does not ahve a “fatigue” limit, so like the ant on the airplane wing it always accrues fatigue. Eventually over centuries and centuries the wing will fail. If the wing were made of steel “technically” it would never fail.
The problem is that the loads put on a bike frame are, again in my understanding, are far above the “fatigue limit” of the material, and thus the frame accrues fatigue, eventually breaking.
A bike strong enough to be made below the fatigue limit would likely be very heavy and bulky.
I’m not an expert either, but thsi is how I understand it.
~Matt
I’m saying that there is a point BEYOND the endurance limit BELOW the yeild that lies within the elastic deformation of the material. That is where a bicycle operates.
Ever broken a spoke? You think it was plastically deformed prior to failure? What are spokes made from again?
-SD
Very interesting links…Thanks.
~Matt
A while back, Trek published a study, so take this with a grain of salt.
The jist of it was that if you bend a steel, aluminum, Ti, and CF frame within flex limits (this means you can’t go and bend it in half, but are rather subjecting it to what it would experience on a daily basis - on a rough day), the steel frame would bend 10x more than the aluminum before it broke, the Ti would bend 1000x more than the aluminum, and CF would ben 10,000x more before it broke.
10,1000, and 10,000 were not the actual numbers, but it was close to that.
I think you’re spot on here and the links posted here
http://forum.slowtwitch.com/gforum.cgi?do=post_view_threaded;post=348670;sb=post_latest_reply;so=ASC;
Would appear to support you.
~Matt