Carbon bikes - environmental disaster?

[duncanm]

ala..

[silentC]

Sounds like a great description for one of my Strava rides "Cycles to failure"...

[human909]

Endurance limits are usually half of the tensile strength. No idea why you referenced young's modulus. Young's is stress/strain relationship, not fatigue.

Quite true....
This is what you should have referred to.

https://en.wikipedia.org/wiki/Fatigue_limit
[/quote]

Technically steel does have an endurance limit (i.e. a theoretical threshold where at a given stress, the material will not fatigue). However this does not really happen in practice, due to one of two things usually:
1. The material will usually exceed the endurance limit at high stress regions.
2. The specimen is always imperfect -especially around welds (notice how lots of failures happen around welds?)

Carbon on the other hand has a much generally has a endurance limit much closer to the tensile strength as opposed to steels which are about half and alus which don't have one at all (or very low stress endurance limit).

I haven't seem much evidence of these assertions both in literature and in real life applications. Though I am the first to admit that the intricacies of fatigue are not my expertise. Get deep into it and it can become quite complex. That said I do design steel structures and vessels all the time that undergo significant cyclical loading and vibration.

Let me know how about the fatigue life of the Eads bridge if you are that worried about fatigue. Almost 150 years and still going strong. Or 85years for the Sydney Harbour bridge...

[fat and old]

Sounds like a great description for one of my Strava rides "Cycles to failure"...

As opposed to mine "failure to cycle"

[Calvin27]

Let me know how about the fatigue life of the Eads bridge if you are that worried about fatigue. Almost 150 years and still going strong. Or 85years for the Sydney Harbour bridge...

You are comparing a bridge to a bicycle design...? Seriously?

Ill bite though. If you do pressure vessels you will know that they have a finite service life (decommission after certain amount of time or uses), are massively over designed and/or they are monitored with ultrasonics or other tech.

If you do bridges you will know that the firstly the safety factors are huge, like orders of magnitudes greater than a bicycle thus the stresses never get near the endurance limit, or the bits that are a routinely replaced (cables for example). They also have routine inspections and modifications along it's life span. Many of them will also have vibration damping as a key design feature.

A bike is different as it is designed a lot closer to the limit, with less safety factors and above all else weight savings as a consideration. Apples and oranges. But nice banter.

[outnabike]

Crap sold by some major manufacturers made from either ally or plastic.
I reckon you can make a product out of any material and get a problem. But going to new materials and design from light components is fraught with long term issues. Here we see even good named manufactures with recalls. I selected a few and I don’t; know if they were app plastic or ally but it doesn’t inspire confidence in their bike lasting as long as a steel bike.
The report doesn’t go into the materials used but as steel is out of the race these days probably not in it. Maybe it is in some of the MT forks.
Just saying. We all should want a bike to last at least till trade in time. If light weight is the goal then we shouldn’t complain about longevity. Light is not meant to have a long life.
………………………………………………………
https://www.consumeraffairs.com/bicycle-recalls
Orbea recalls Avant bicycles
The bicycle front fork can crack
09/04/2014 | ConsumerAffairs
………………………………………………
Specialized Bicycle Components Recalls Bicycles
A problem with the front fork poses fall and injury hazards
……………………………………………
Cycling Sports Group recalls GT mountain bicycles
The handlebars can crack, posing a fall hazard to the rider
06/09/2017 | ConsumerAffairs
……………………………………………………..
SCOTT recalls bicycles with SYNCROS seat posts
The seat post can break, posing a fall hazard
05/20/2016 | ConsumerAffairs
……………………………………………………………………
Shimano Dura Ace Bicycle Wheels Recalled
10/23/2008 | ConsumerAffairs
…………………………………………………………..
Salsa Bicycles Recalled
CroMoto S.U.L. handlebar stems were also sold individually
02/26/2009 | ConsumerAffairs
……………………………………………………………………
Felt Cyclocross Bicycles Recalled
08/19/2009 | ConsumerAffairs
……………………………………………………………….
Giant Recalls TCR, SL Bicycles
01/14/2009 | ConsumerAffairs
……………………………………………………………………

[Comedian]

I also mentioned a few pages back that it has no theoretical fatigue limit. That is you can keep stressing it over and over and it shouldn't ever develop cracks provided the specimen doesn't have flaws to begin with. Steels do have a fatigue limit and aluminium is even lower than steel (i.e. lss cycles before it develops cracks). For bicycles with high cyclical loading this is a pretty important property.

Sorry. That's incorrect. Steel and titanium do not have fatigue limits, as long as they are bent less than youngs modulus. Good frame builders will ensure that steel and titanium frames do not bend in normal use beyond this point - giving them indefinite life.

https://en.wikipedia.org/wiki/Young's_modulus

Aluminium on the other hand doesn't have this property. Each time it bends is one less time it can bend before it breaks. Good frame designers ensure that high stress aluminium parts don't bend so as to get around this.

Endurance limits are usually half of the tensile strength. No idea why you referenced young's modulus. Young's is stress/strain relationship, not fatigue.

This is what you should have referred to.

https://en.wikipedia.org/wiki/Fatigue_limit

Technically steel does have an endurance limit (i.e. a theoretical threshold where at a given stress, the material will not fatigue). However this does not really happen in practice, due to one of two things usually:
1. The material will usually exceed the endurance limit at high stress regions.
2. The specimen is always imperfect -especially around welds (notice how lots of failures happen around welds?)

Carbon on the other hand has a much generally has a endurance limit much closer to the tensile strength as opposed to steels which are about half and alus which don't have one at all (or very low stress endurance limit).

Yes thanks I got my terms wrong there.

[Comedian]

I've got a 25yo carbon (composite) frame going just fine. I can easily see it going another 15.

Go on.. details! What brand and model, what structure (all CF or a mix of aluminium or something else)? Do you have any idea of the K's? Has it been in mainline use for 25 years or has it drifted into retirement?

The highest mileage frames that I know of personally where I trusted that the owner really knew was 160k. If yours is 25 and still going and in mainline service then it could be the highest mileage I've ever heard of fairly easily..

[human909]

You are comparing a bridge to a bicycle design...? Seriously?

Yes and no. We were talking about fatigue here. And you were expressing concerns about steel's fatigue life. You were massively overstating the issue and I brought up an old steel structure as an example.

Ill bite though. If you do pressure vessels you will know that they have a finite service life (decommission after certain amount of time or uses), are massively over designed and/or they are monitored with ultrasonics or other tech.

Depends, depends, depends. But not really relevent to start talking about standards and everything here. Afterall pressure vessels are a extremely broad range. But no, I wouldn't say they are "massively over designed", but hey maybe your definition of massive is different from mine.

Try pumping your tyres up to 5x maximum pressure and tell us how it fairs... Come on, I am curious.

If you do bridges you will know that the firstly the safety factors are huge

Um... No really they aren't "huge". And for starters safety factors isn't really how it works so I don't think we can have a sensible discussion about this because that isn't how structural designed is approach at least in this country.

like orders of magnitudes greater than a bicycle

Gotta disagree here too.

Given that large bridges have the largest loads being self weight one could readily conclude that a bridge's typical load is closer to it's limit states. (Earthquake and wind may or may no have a significant bearing here obvious depends on circumstances. And your statement about orders of magnitude? Many bridges would collapse with a simple DEAD LOAD an order of magnitude higher.

But why are we talking safety factors again?

They also have routine inspections and modifications along it's life span.

Yep and that doesn't magically increase the fatigue limit.

Many of them will also have vibration damping as a key design feature.

*cough* Speed wobbles *cough*

[Duck!]

Vibration damping and speed wobbles are different things. Vibration damping is the response to high-frequency input and primarily due to the ability of the material to absorb the vibrations. Composites are good at this because the resin component of the layup is slightly compressible and very elastic, so will absorb rather than transmit vibration energy. Steels and titanium can also have good vibration damping because they have good elasticity, but due to lower compressibility compared to composite rely more on the ability of the respective tubes to bend to absorb the vibrations. However individual alloys and heat or chemical treatments can greatly affect the elasticity and damping ability.

Speed wobbles are an extension of harmonic resonance, which is more related to the geometry of the structure than its material, but not entirely separated. Harmonic resonance begins with a low-frequency energy input, such as a steering movemrnt in a bike perspective, but rather than the stucture absorbing the deflection, it returns and reinforces it, leading to a deflection/correction cycle of ever-increasing magnitude, which will eventually conclude with a crash, bridge collapse or "death roll" in sailing (being a yachtie in another life I had to throw that in ) unless something is done to upset the harmonic. One of the most dramatic examples of harmonic resonance is the Tacoma Narrows Bridge collapse; the broad but very shallow profile of the bridge deck fluttered like a ribbon in a strong wind, until it literally shook itself apart.

[human909]

Funny you mentioned the Tacoma Narrows bridge. I almost did the same. But I figured there wasn't much point going further. What you describe there are both 'vibrations', merely different frequencies and modal patterns...

Different but also the same. Thus lots of what you have said is quite true but to suggest harmonic are not 'vibrations' is kinda losing sight of things...
https://en.wikipedia.org/wiki/Vibration

Harmonic resonance begins with a low-frequency energy input

Low frequency? You are missing the point. The frequency of the energy input depends on the resonance of the object. The examples you used did have very low very frequency inputs, of the order of .1 to 10hz...

Here is example of a higher frequency energy input:
https://www.youtube.com/watch?v=CdUoFIZSuX0

[duncanm]

I've got a 25yo carbon (composite) frame going just fine. I can easily see it going another 15.

Go on.. details! What brand and model, what structure (all CF or a mix of aluminium or something else)? Do you have any idea of the K's? Has it been in mainline use for 25 years or has it drifted into retirement?

The highest mileage frames that I know of personally where I trusted that the owner really knew was 160k. If yours is 25 and still going and in mainline service then it could be the highest mileage I've ever heard of fairly easily..

cadex CFR-1. Bonded carbon tubes on Al (head, seat, BB, dropouts) and Al forks (which concern me the most regarding failure).

Grandpa's axe -- the cranks, stem and bars are as purchased - everything else has been replaced at some point in time due to wear and upgrade (to 9sp brifters, for example).

No idea of total mileage, I don't expect its too high, but its in regular commute usage (N=1) and I've racked up approx 16k on it since 2013 (says strava). I think I purchased it about about 4 years before that when I was doing longer commutes. So lets say 30k in my hands.

Google says CFR-1's were sold ~93/94.

Frame has actually failed on me once -- rear dropout debonded from the chain stay (A known failure mode for these frames is the carbon tube to Al glue failing). The fix was fairly straightforward with a bit of cleaning and epoxy in the joint.

[Calvin27]

You are comparing a bridge to a bicycle design...? Seriously?

Yes and no. We were talking about fatigue here. And you were expressing concerns about steel's fatigue life. You were massively overstating the issue and I brought up an old steel structure as an example.

Many of them will also have vibration damping as a key design feature.

*cough* Speed wobbles *cough*

Yea nah. A bridge is not even close to a bicycle design wise. Not sure what I massively overstated. Steels do have a fatigue life that is a lot less favourable than carbons. Sorry if you are offended by this.

Speed wobbles are due lack of vibration dampening now? Really? This only gets better!

[Lukeyboy]

If you want to see a prime example of speed wobbles put a TT water bottle carrier on the back and load it up with 3 full water bottles. Take your hands off the bars and see what happens at 20/25/30/35/40kph.

[CKinnard]

If you want to see a prime example of speed wobbles put a TT water bottle carrier on the back and load it up with 3 full water bottles. Take your hands off the bars and see what happens at 20/25/30/35/40kph.

From my extensive testing with a wobble bike, the most reliable thing to do to stop wobbles is get your weight down and way forwards.
It's similar to motorbikes where they recommend you lie down flat on the petrol tank.

[Nobody]

Many "supersport" (track orientated) motorcycles come with steering dampers.

Settings were updated to match the new dimensions and handling characteristics. Öhlins’ special twin-tube design ensures stable damping performance even under circuit-riding conditions, and enables superb kickback absorption. The damper’s high precision construction and use of an integrated clamp help minimise friction as the damper piston slides back and forth. Initial motion is very smooth as a result. Steering damper body is finished with ahighly scratch-resistant alumite1coating.

http://kawasaki.com.au/shop/motorcycles ... t-replica/

[human909]

Speed wobbles are due lack of vibration dampening now? Really? This only gets better!

Yes. I believe your confusion lies in a narrow definition of vibration.

That said, I would normally avoid the term vibration in describing speed wobbles due to confusion with higher frequency harmonic motion (aka 'vibration' that you are referring to) compared to the lower frequency harmonic motion (eg speed wobbles).

Either way there is no need to try to mock me, especially when you fail to grasp the basics.

[Calvin27]

Speed wobbles are due lack of vibration dampening now? Really? This only gets better!

Yes. I believe your confusion lies in a narrow definition of vibration.

That said, I would normally avoid the term vibration in describing speed wobbles due to confusion with higher frequency harmonic motion (aka 'vibration' that you are referring to) compared to the lower frequency harmonic motion (eg speed wobbles).

Either way there is no need to try to mock me, especially when you fail to grasp the basics.

Not sure where I am mocking? I mentioned that a lot of bridges have vibration dampening to reduce fatigue stress (i.e. design it to move in controlled way) and you compared it to speed wobbles. Not sure why you thought it necessary to 'cough' at speed wobbles when it doesn't have anything to do with the longevity of different frame materials.

[human909]

Not sure why you thought it necessary to 'cough' at speed wobbles when it doesn't have anything to do with the longevity of different frame materials.

Lower frequency vibrations absolutely can affect longevity of materials.

It was mention because to my knowledge dampers used in bridges are more commonly used to stop the lower frequency effects of oscillation. Hence the mention of speed wobbles and Tacoma Narrows. These lower frequency effect can readily cause fatigue.

[Calvin27]

It was mention because to my knowledge dampers used in bridges are more commonly used to stop the lower frequency effects of oscillation. Hence the mention of speed wobbles and Tacoma Narrows. These lower frequency effect can readily cause fatigue.

Now you are comparing speed wobble to a bridge damping system and linking it to fatigue? Not sure what to say anymore.

[human909]

Now you are comparing speed wobble to a bridge damping system and linking it to fatigue? Not sure what to say anymore.

'Vibration' aka harmonic motion is the link as has been explained numerous times. But I think this off topic discussion has run its course.

[CXCommuter]

Speed wobbles are due lack of vibration dampening now? Really? This only gets better!

Either way there is no need to try to mock me, especially when you fail to grasp the basics.

Bwahahahahahaha Biggest Pot ever calling the Kettle Black

Calvin just agree with Human909 he knows everything

[biker jk]

Speed wobbles are due lack of vibration dampening now? Really? This only gets better!

Either way there is no need to try to mock me, especially when you fail to grasp the basics.

Bwahahahahahaha Biggest Pot ever calling the Kettle Black

Calvin just agree with Human909 he knows everything

For some, there are no known unknowns.

[baabaa]

It was mention because to my knowledge dampers used in bridges are more commonly used to stop the lower frequency effects of oscillation. Hence the mention of speed wobbles and Tacoma Narrows. These lower frequency effect can readily cause fatigue.

Now you are comparing speed wobble to a bridge damping system and linking it to fatigue? Not sure what to say anymore.

well, for a start I strongly suggest from this point of time, that Brake Bridges now be referred to, if not re-named in all BNA forum discussions as Break Bridges....

[mikesbytes]