[ATN]

I am looking at a RM Vertex Team Scandium from 2000.

How does Scandium compare to Aluminum as to fatigue life? Also, if you own thie frame, do you find that the tubes are butted/drawn too thin, or does it feel solid?

 

[ohio]

Originally posted by ATN

How does Scandium compare to Aluminum as to fatigue life?

Don't have the frame, but scandium does have a better fatigue life than aluminum... however, when was the last time you saw an aluminum frame break from fatigue? Aluminum frames are designed super stiff so that basically won't ever happen. Hell, even noodly aluminum frames like Vitus road bikes are still going strong.

So the advantage of a scandium frame isn't that it will last longer... it's that it can use smaller diameter tubing. This means a less stiff frame, and slightly thicker walls (dent resistance).

 

[ATN]

Up here on the shore aluminum frames break from so much you don't even take the time to figure out what broke it!

I am wary of a 3 year old aluminum hardtail... I wanted to know if scandium, being lighter, would cause me problems down the trail. I know it makes a light frame (2.9 lbs, and Rocky makes 'em heavy) that rides great.

I'm also trying to figure out how good of a deal it is, even if I only get a season out of the frame.

 

[oldfart]

Aluminum frames are so stiff they don't fatigue? Well they are better designed with better materials today versus 5 or 6 years ago, but all frames no matter what they are made from will eventually die. The question is when. Grandpa riding only Sundays on a Banshee Scream will likely die before his frame, but used as intended, some hucking fool will probably cause some damage eventually.

Thet add Scandium to alluminum to make the aluminum stronger which means they can use less of it to achieve the same strength at a lighter weight. Anything superlight will not have a super strength or life. If it was some ones race bike for a couple hard seasons, don't pay much. And examine the underside of the downtube at the headtube in particular and all other junctions in general for cracks. Something we should all do to our own bikes regularly anyway just in case.

I have cracked steel and aluminum bikes, I know a fellow who broke two titanium Lightspeeds. I've seen busted carbon bikes. No material is failure proof particularly when its very light. Keith Bontrager says, "light, strong, cheap. pick two of those properties for bike equipment and it won't be the third.

 

[ATN]

Thing is it is under a grand CAD for the complete bike with full 9.0 SL, z2 flylight's, RF cranks (next lp's I think), mavic 517's (i think again), and RaceFace's lightest bars, stem, and a carbon seatpost. V brakes unfortunately, but that's part of the "pick 2".

It was someone's race bike, Ben Stigson, Rocky Junior XC racer. I got his dad's phone number, I'm going to track Ben down.

 

[ohio]

alright kids, maybe I should have been more clear.

FAILURE AND FATIGUE ARE NOT THE SAME THING.

fatigue failure is only one kind, and almost NEVER happens with bicycles. The exceptions to this are when there are stress risers caused by poor design or welding. People often confuse fatigue with the paper-clip effect... NOT the same. Paper clip effect requires plastic deformation in each cycle. Fatigue is only when the material undergoes cyclical stresses that do NOT exceed the yield strength.

And they add scandium to aluminum to decrease the crystal structure grain size, which improves the fatigue characteristics. See abhove for the rest. The specific strength is actually not much higher than 7005.

In 3 years of riding, dude will NOT fatigue a frame. He may however have beaten the crap out of it, causing plastic deformation (or crack propogation if there are bad welds) which wouold compromise the strength of the frame.

 

[Babar]

I got 2002 RM VTSC right now i have looooooong way to go.

 

[ATN]

If this was a 2002 frame I'd be on it like Richard Simmons on gay porn...

How much did that one run you Babar?

 

[Babar]

$600 USD on clearance but they sold out... I think the new 2003 frame is $1200.

 

[ATN]

New is out of my price range then...

 

[Joe33]

Originally posted by ohio
alright kids, maybe I should have been more clear.

FAILURE AND FATIGUE ARE NOT THE SAME THING.

fatigue failure is only one kind, and almost NEVER happens with bicycles. The exceptions to this are when there are stress risers caused by poor design or welding. People often confuse fatigue with the paper-clip effect... NOT the same. Paper clip effect requires plastic deformation in each cycle. Fatigue is only when the material undergoes cyclical stresses that do NOT exceed the yield strength.

And they add scandium to aluminum to decrease the crystal structure grain size, which improves the fatigue characteristics. See abhove for the rest. The specific strength is actually not much higher than 7005.

In 3 years of riding, dude will NOT fatigue a frame. He may however have beaten the crap out of it, causing plastic deformation (or crack propogation if there are bad welds) which wouold compromise the strength of the frame.

Ive never broken a frame from just one gigantic hit. both times its happened on a smaller jump. Neither of them broke on a weld. When I broke my handlebars it happened when I was pulling up rather taking a hard landing. How is that not fatique?

 

[shootr]

well ohio, said some stuff that I agree with and some that I don't.

Fatigue, CAUSES failure in aluminum.
the fatigue endurance of 7005 aluminum is 23ksi, (14ksi for 6061)Fatigue strength is defined as the resistance of a material to failure under cyclic loading. It is generally expressed as the stress range giving a 50% probability of fracture after a given number of load cycles. It is greatly influenced by the conditions of loading

this means that at a specific non-rupture or elongation level of force certain materials (ones with fatigue endurance thresholds) the material WILL eventually suffer a fracture.
THIS IS FAILURE
This also happens to be one of the PREDOMINANT causes of failure in aluminum bicycle frames and components.
At the design level these components are designed to withstand a given level of instantaneous loading, these parameters are based upon what will the expected loads based on application.
(ie, a XC frame will be designed around a much lower expected loading vs. a DH frame)
This takes care of failures due to stress caused by significant instantaneous loads in the expected range.
BUT, unfortunately since aluminum and it's alloys have a fatigue endurance threshold, the cyclic (or repetive, in laymans terms) loads and stresses that the frame sees CAUSE failure of the material after a certain number of cycles, this number is a factor of the level of load. higher loads reduce the number of cycles to cause failure.
The reason that failures tend to show up at joints near welds and similar locations, is that the joining process often leaves "stress risers" or portions of the material that has a different grain structure compared to the base material, and the cyclic loading fails this portion first, as the differing grain structure usually has a much lower fatigue limit.

there is a thing that occurs in aluminum alloys, whether they use silicon, lithium, or other substances to alter the strengh/weight characteristics...
What happens is that joining them thru fusion welding processes become increasingly difficult, as they become more prone to stress risers, and therefore require special procedures and considerations to prepare them for welding.
So though scandium alloys themselves may be less fatigue prone, their unions (*IF fusion welded) may be MORE prone to fatigue.
Fatigue damage is extremely difficult to detect, and impossible to detect visually, there are speciallized methods for detection (NDT methods) but they are cost prohibitive in regards to bicycle frames, (yes even those really expensive ones),
THEREFORE I would NEVER buy a three year old frame, as even though it may APPEAR perfect it could be extremely close to it's rupture point.

Rupture or plasitic deformation is obviously much easier to detect. it is the crack you see, the broken part etc. but in aluminum it is VERY often a symptom of fatigue, and VERY rarely a symptom of excessive instantaneous loading.
I could go alot further into this, but my answer is already tiringly long.
hope that this helps
(just like in the old days eh Ohio)

 

[shootr]

of course this answer applies to everything EXCEPT in the case of Rocky Mountain RM series bikes.
These as we all know have and will fail due to instantaneous loading..
hence the "quick release rear swingarm"

 

[shootr]

for some fairly concise, but not overly scientifically versed explanations you can check out this site:
information on fatigue failure

 

[ohio]

Originally posted by Joe33
How is that not fatique?

See my explanation on the difference between fatigue failure and "paper clip effect." It is POSSIBLE that it was from fatigue, but I think it is more likely that it was from previous impacts that EXCEEDED the yield stress of the material.

Originally posted by shootr
for some fairly concise, but not overly scientifically versed explanations you can check out this site:
information on fatigue failure

From that paper:
"For fatigue fracture to occur, there must exist cyclic plastic strains. Thus we shall need to understand the behaviour of materials subjected to cyclic plastic deformation."

This is different than the definition in every solids text I have ever used. According to everything I was taught, "fatigue" applies to cyclical stresses BELOW the yield stress of the material, in the elastic region... NOT plastic deformation. If you're using the definition from that paper (which is the "paper clip effect" or failure resulting from previous yielding and work hardening), then YES, almost all aluminum frame failures are from fatigue. If you use mine, which I believe is the more traditional definition, then that is not the case. Yes, all aluminum will eventually fail from fatigue, but I'm saying that failure usually results from repeated plastic deformations long before that.

 

[shootr]

I agree Ohio, I dont' know why I missed that , if you note in my explanation I state that the cyclic loads are imparted in the elastic not plastic phase of deformation

But I still stand by the fact that failure occurs as a result of a grain change caused by the repetitive cyclic loads that do not exceed the elastic phase. This change in grain leads to a shear location at which a microscopic crack propogates from.
after this point, which IS a failure of the material, its deformation continues into the plastic phase (paper clip effect), as the crack elongates and deepens which leaves less material to support the forces imparted and which in turn causes a higher stress loading upon the remainder, (= load over given area, area reduced strain increases), which in turn causes greater failure, which in turn reduces the remaining material to support the loads and so on.
Then finally is the "catastrophic failure" which is the complete separation of the peices.
Do not confuse the MODE of failure with the CAUSE of failure.
you stated that "fatigue failure is only one kind, and almost NEVER happens with bicycles" , well technically Fatigue is NOT failure, (as you originally opened with and I wholeheartedly agree with.
Fatigue only LEADS to failure (or put another way, failure is a symptom of fatigue)....but it is certainly the MOST common cause of failure in Aluminum frames
The confusion comes from the fact that we can see failure, but not fatigue, as it occurs at microscopic/molecular levels.

that all said, I still stand by the fact that ANY aluminum alloy frame, no matter what condition it appears, if ridden has been subject to fatigue, which definetely reduces its lifespan.
so with any used frame it is truly buyer beware, as no amount of engineering can oppose the physics of fatigue, it CANNOT be engineered out of these alloys.
This is not the case with ferrous alloys.
as they do not generally suffer fatigue (understanding that a material is considered to have an infinite fatigue endurance when it can handle 10 million cycles at 50% of it's deformation threshold force).
So if you are buying a used frame consider very very carefully if it is not a chromoly or Ti frame (as Ti is also considered to have an infinite fatige endurance)

edit: I would consider the statement in my earlier given resource regarding fatigue to occur in the Plastic phase to be wholly false and should be dissregarded, as I said I only entered that resource as a "simplified" source, it is NOT a resource that I would or have used, I searched it out as a "simplified definition of fatigue"
Plastic deformation is failure of a material, whether that deformation is intentional or not, (intentional beint the shaping of material by physical force, ie bending) because the material enters it's plastic phase it is indeed in a MODE of failure.
sorry for any confusion this caused

good to debate with you once again Ohio

 

[ohio]

Originally posted by shootr
This is not the case with ferrous alloys.
as they do not generally suffer fatigue (understanding that a material is considered to have an infinite fatigue endurance when it can handle 10 million cycles at 50% of it's deformation threshold force).
So if you are buying a used frame consider very very carefully if it is not a chromoly or Ti frame (as Ti is also considered to have an infinite fatige endurance)

good to debate with you once again Ohio

always a pleasure.

I'd like to add to that last statement, that almost NO bike on the market, chromoly or otherwise, is designed to have an infinite fatigue life. If you properly designed a steel frame with a 2.5X safety factor using a 50% YS limit under max loading, you'd probably end up with a 10lbs or more hardtail...

Most frames don't even have THAT much thought put into them, but if they did, they're designed not to fatigue under usual cyclic loading (pedalling forces, braking bumps, rock gardens), and to handle several 1000 (rather than several million) MAX loadings (big hits)... which means even on a steel frame, you will be exceeding the fatigue threshold, but it's probably not going to fatigue in your lifetime.

 

[shootr]

Actually Ohio, I was refering to the requirement for a material to be considered to have no fatigue endurance limit.
Not the design consideration.

Ferrous alloys generally are considered to have an infinite fatigue endurance limit meaning that unless the elastic phase envelope is breached (leading into plastic phase, and permanent deformation), there is NO grain structure change..
Theoretically suggesting that in these alloys that any amount of deformation that occurs in this elastic phase will not be detrimental to the life of the component.

wow. after looking back at what I wrote it is not super clear (layman wise) but I am sure that you understand what I am saying perfectly.

Design factors cannot truly encompass fatigue endurance as this variable is too difficult to extrapolate. Design characteristics usually focus mainly upon maximum instantaneous loading, and one would engineer the structure to exceed the expected max load. This is the yeild threshold and not to be confused with the fatigue threshold..
ALL materials have a yeild threshold.
not all materials have a fatigue threshold

 

[math2014]

SO allu dies eventually (faster than a usual man) whereas Steel or Ti doesnt. In my honest opinion, Steel also dies in a mountain bike because of internal rust . I was also concerned with the lifespan of my frame (allu) but then again many quality cars and motorbikes use allu for frames. These constructions endure well more than 10yrs (Audi 12yrs warranty) so my bike should at least last that long doing aggro-xc . That said after 5yrs i ll have enough money and taste to change to another bike just for the change .

 

[shootr]

Originally posted by math2014
SO allu dies eventually (faster than a usual man) whereas Steel or Ti doesnt. In my honest opinion, Steel also dies in a mountain bike because of internal rust . I was also concerned with the lifespan of my frame (allu) but then again many quality cars and motorbikes use allu for frames. These constructions endure well more than 10yrs (Audi 12yrs warranty) so my bike should at least last that long doing aggro-xc . That said after 5yrs i ll have enough money and taste to change to another bike just for the change .

This is not the same. In fact because of what it is alloyed with, 4130 is actually fairly corrosion resistive (chromium and nickel has that property)..So "internal rust" is NOT a concern.
and comparing your bicycle to cars or motorcycle frames for an indication of lifespan is unfortunately fairly useless, as these are subject to very different types of cyclical loads.