Carbon rip off (vs Aluminium)

[MintSauce]

Christie' date=' you say better fatigue life compared to Titanium, is this true. I thought that Ti would outlast Riaan Cruywagen[/quote']

Nothing will outlast Riaan!!!!


So what alu frame compares with, lets say, Cervelo Soloist? Where does the stiffness of bike come in?
Why do people say their frames gets 'pap' after a couple years and needs to be replaced?

 

 

Let me translate for all the Hubbers.....:

 

blah-blah blah-blah blah-blah blah-blah I'm getting a Cervelo Soloist next week blah-blah blah-blah blah-blah blah-blah

 

 

 

 

 

 

[Marius]

and one more point I?d like to add, Cycling is probably the most expensive sport ever and commen sense has absolutely no place in cycling, just look at the ridiculous prices we pay for ?useless? parts and services, you have to be slightly brain washed to spend the money and by the sounds off it you still not there yet, good for you, fight the power!<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[greatwhite]

Spot on' date=' greatwhite  While some carbon composites have a superior stiffness to mass ratio, better structural damping and vastly superior fatigue life compared to most other frame materials (steel, aluminium, titanium), it is not ideal for all components. Stems are a good example - Eastons EC90 stem weighs the same as the EA70, but costs 3x more.

 [/quote']

 

I have no idea what structural damping is, maybe you can explain to us, but for all the other benefits you mention such as fatigue life, needs to be put into perspective. The fatigue life of a properly designed steel or aluminium bike exceeds your or my lifetime. In other words, it is strong enough and strong enough is strong enough.

 

 

But lets say for a minute that it is stronger and it matters. Last week, whilst washing my aluminium bike, it fell over onto a sharp tile and dented the seatstay. I fussed about a bit, rubbed the scratch and then went for a ride. Imagine that happing to a carbon bike. That area would have been pulp and I'd have a new frame by now. Still strong enough?

 

Stronger is not always stronger.

 

 

Agreed on the comment about denting ali vs snapping carbon - was going to say that in my original post, but figured I'd said enough already.

 

As for fatigue life, I'm a big lad and I work on 3 years for a frame - if it hasn't broken by then, I'm very pleased - all failures happen in the BB area:

In the case of my early steel frames, it would appear crystaline break down of the manganese molybdenem steel alloy (Reynolds tubes) due to over temp during brazing might have been contributory in some cases, but the failures we typical cyclic fatigue failures

My titanium pinarello failed at the bottom of the front deraileur hanger, again typical high cycle fatigue. I suspect the crack propogated from a tiny weld notch but could never find it.

Aluminium frames will always fail eventually given aluminiums lack of a cyclic fatigue limit - my experience bears this out.

I've never broken a carbon bike - I'm on my 1st one at the moment, but its a race only bike, so should last a while.

 

Getting to the point - "The fatigue life of a properly designed steel or aluminium bike exceeds your or my lifetime" - yes, if you want it to weigh a lot more. A modern race frame is basically a sacraficial component. There are no meaningful safety factors to cover fatigue etc. The lighter and more expensive it gets, the more this is the case.

 

The solution was simple - find a manufacturer that makes all their frames to the same geomtry, get their race frame and get their tank frame. In my case I have a CR1 limited for racing and an old speedster s4 (heavy 1.6kg ali) to train on.

 

And, I believe, appropriate application of carbon and ali

 

[FanieFiets]

 

 

 

Let me translate for all the Hubbers.....:

 

blah-blah blah-blah blah-blah blah-blah I'm getting a Cervelo Soloist next week blah-blah blah-blah blah-blah blah-blah

 

 

 

 

 

 

 

[greatwhite]

and one more point I?d like to add' date=' Cycling is probably the most expensive sport ever and commen sense has absolutely no place in cycling, just look at the ridiculous prices we pay for ?useless? parts and services, you have to be slightly brain washed to spend the money and by the sounds off it you still not there yet, good for you, fight the power!<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[/quote']

 

You're right, too many cyclist are suckers for marketing, to a degree myself included.

 

In the top echelons of cycling carbon (and lots of it) has its place, but in the mid range, don't dismiss ali as inferior, because often its actually a better option.

[NotSoBigBen]

and one more point I?d like to add' date=' Cycling is probably the most expensive sport ever and commen sense has absolutely no place in cycling, just look at the ridiculous prices we pay for ?useless? parts and services, you have to be slightly brain washed to spend the money and by the sounds off it you still not there yet, good for you, fight the power!<?:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[/quote']

 

 

Oh and M, I have as you may have noticed lost this battle long time ago !

 

But I aint moaning as I spent it willingly on something I wanted  (could just about afford at times!) and enjoy, I think there are only a minority of cyclists who do not buy on impulse or at least go with their heart in some cases rather than the opinions of hubbers others!

 

It also helps if it is a bit of eye candy as well, so for some (me included!) carbon is cool!

 

But ja whateva blows your hair back!

[Minion]

Some quick notes on fatigue:

 

The way to compare materials subjected to high-cycle fatigue is principally through the use of an S-N curve of Stress vs. Cycles to failure. These curves are derived by submitting a given material geometry to a fatigue load (usually fully reversed bending) until it fails. By changing the load and recording cycles to failure you get a curve like this one for Aluminium and steel:

 

http://www.tokuroglu.com/SNCurveAlveSteel.jpg

 

The interesting thing to note from this curve is that the steel has an endurance limit of ~320 MPa. This means that if the stress amplitude experienced by the steel specimen is kept below 320 MPa it will never fail due to fatigue. The aluminium does not have an endurance limit - no matter how low the loading amplitude it will eventually fail.

In general, most steel and titanium alloys have an endurance limit. Aluminium alloys to not have such a limit (this is the reason why aircraft much eventually be retired from service).

 

Fatigue failure occurs when a crack starts (initiation) and grows with repeated loading (propagation) until failure. Cracks will almost always initiate from a stress raiser. This could be something like a scratch or notch where you've knocked the frame, a pore (hole) in a weld or from improper fibre lay-up, grain boundaries between metal crystals or even pitting cause by corrosion. Accounting for all of these factors is what makes design for fatigue difficult.

 

Ultimately though, as Johan mentioned, the loading cycles to failure will generally exceed our lifetimes and you are certainly more likely to lose/crash/break/have stolen/get bored with the frame before fatigue failure starts to be an issue.

 

On structural (or hysteretic / material) damping:

 

A structure subjected to vibration can be idealised as a series of masses connected by springs and dampers, like those shown here:

 

http://upload.wikimedia.org/wikipedia/en/thumb/7/79/Mass_spring_damper.png/200px-Mass_spring_damper.png

(Wikipedia. Applies to Coulomb damping. Hysteritc damping is more complex as the damping force and excitation velocity are not in phase)

 

Stuctural damping is the property of the geometry and the material that acts to dampen out vibrations. In a system with no (or very low) damping any vibrations set-up in the system will not die down over time - if you hit it the vibrations will not stop. Conversely, high damping will cause vibration to die down very quickly.

The damping also determines how effectively the structure transmits vibration. High damping (e.g. rubber) transmits very little. Low damping (eg Steel) transmits most of the vibrations.

 

[Christie]

 JB, to answer your question: Structural damping is the small frictional energy loss coupled to elastic stress. The exact molecular origin for this phenomenon remains unknown, as far as I know. If designed so, carbon composite can have more structural damping than steel or aluminium. It depends on the type of fibre, the matrix and the lay-up. 

 

FF about fatigue properties: depends on how well it was designed. The fatigue life of the titanium is superior to steel & aluminium, but way, way less than carbon/epoxy. (Dilbert has some SN curves somewhare) I have never analysed a bicycle frame, but I would guess that the stress levels in a frame is very very low most of the time, so comparing fatigue curves is a bit of an academic excersize. I agree completely with JB, a properly designed frame will last forever, regardless of frame material.

 

Faniefiets, about frames going soft with age: I can not think of anything that will cause this. Nothing I know of will reduce the stiffness of a frame over time.  Fatigue will cause it to crack, not to "go soft" I think it is all in the mind.  

[Gumpole]

haha,

 

to put this in perspective compare the power that will rip the wings off an aeroplane VS the power that a bicyclist will produce... its ridiculous.

 

all this science is fine, just largely irrellevant to cycling.

[Minion]

 

all this science is fine' date=' just largely irrellevant to cycling.[/quote']

 

True, but it's fun for an engineer and allows us to skive off work while pretending that we are actually doing work

 

[Cois]

To lazy to read all.  I have a Alu fork  kills me on the road.  Swapped to carbon.  Man it is a blessing. It rides much softer than Alu

[gerhard]

 Mr PV I also want to know that person where I can get the same rim as a easton without the branding

[linnega]

The frames "going soft" is one of those legends that cycling is built on.  Probably time to let that go the way of some others:

- Smoking before a big mountain opens your lungs;

- Brandy is the on-bike drink of choice;

- Steak for breakfast is the best pre-race meal;

- Red bikes are fastest

[AndreZA]

The frames "going soft" is one of those legends that cycling is built on.  Probably time to let that go the way of some others:

- Smoking before a big mountain opens your lungs;

- Brandy is the on-bike drink of choice;

- Steak for breakfast is the best pre-race meal;

- Red bikes are fastest

 

Hey, the last one is true.

 

 

[nellie]

Also not a big carbon fan...i have a carbon fork (which i think is necessary on a road bike) and my stays are also carbon which is fine, but all in all i love aluminium, either full alu or a carbon-alu mix, don't think i'll swich to full carbon anytime soon.

As for;

 

carbon bottle cages - those normal RavX ones (+/-R40??) are a bit heavier, but they're still working while quite a few of my friends have had to replace their carbon goodies (@ around R200 a piece) when the little thingy at the bottom broke off and their bottles are falling through.

 

carbon stem - the Richie Pro Comp works just as well and i quite like the look of it

 

carbon cranks - well........if it's campag maaaaaaaaaybe i'll go for it, but i liked the old campy look more

 

carbon seatpost - i've got one on my mtb, not bad, and actually looks good as the only carbon part on my mtb, but i didn't like it on my road bike

 

same goes for most other things...

[AndreZA]

 

carbon bottle cages - those normal RavX ones (+/-R40??) are a bit heavier' date=' but they're still working while quite a few of my friends have had to replace their carbon goodies (@ around R200 a piece) when the little thingy at the bottom broke off and their bottles are falling through.

 

[/quote']

 

Nellie, here at the 94.7 expo I bought 2 carbon cages from Rapid Sport (the clothing people) They are only 23g ea. Was only R139 ea and they supplied a little mettal bracket that fits underneath the bottom tab so that it does not brake off. If you choose to use it without and the tab do brake off, then you can just atache the bracket and you can use the cage again. Phone Rapid Sport, they are a CT company.