Go Back  Bike Forums > Bike Forums > Bicycle Mechanics
Reload this Page >

How strong actually is carbon fibre?

Notices
Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

How strong actually is carbon fibre?

Old 09-23-21, 03:37 PM
  #76  
Hondo6
Senior Member
 
Join Date: Sep 2021
Location: SW Florida
Posts: 136

Bikes: Yes

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 45 Times in 30 Posts
Originally Posted by smashndash View Post
hm. Just based off the abstract it seems that I'm talking about translaminar fracture of UD structures under tension. That's probably the closest I'm gonna get to seeing a fatigue test of raw CF.

https://drive.google.com/file/d/1_QX...w?usp=drivesdk

I'm gonna be a pirate and share this for a few days for anyone who's interested. I'll read this in the next couple days and come back if I find anything interesting.
If you find anything interesting, please post your results here if you don't mind. CF is newer material and has more complex behavior than most other common structural materials. Authoritative info about its behavior doesn't seem to be as readily available. I'd be glad to see anything relevant myself.
Hondo6 is offline  
Old 09-23-21, 04:01 PM
  #77  
Harold74
Senior Member
 
Join Date: Jul 2020
Location: Calgary, AB Canada
Posts: 207

Bikes: 1992 Miyata 1000, 1997 Trek 730, 2001 Airborne Zeppelin, 1980+ Nishiki Olympic

Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 30 Times in 21 Posts
I'm a structural engineer who designs buildings and I very much prefer metal bike frames to carbon ones for my own personal use. When a building fails, it's almost never properly constructed members that fail but, rather one of the following:

1) Connections. I would expect this to be true of bicycle frames as well and in this respect, I am hesitant to trust connections between carbon elements and other stuff. In my opinion, the fact that many bike components must be carefully torqued to attach to carbon supports my skepticism.

2) Improper construction. In some respects, I feel that the situation with a home bike mechanic is analogous. Airplanes use carbon but, then, they are only worked on by serious pros under conditions of intense quality control. Should I really be trusting me to swap out a stem on my carbon steerer tube? Probably not given the potential consequences for my face. But I do it anyhow.

3) Damage. Given a long enough time horizon, damage is inevitable via corrosion, impact... whatever. Since potential damage is difficult for a home mechanic to identify, this makes purchasing a used carbon frame or component pretty scary in my opinion.

I have an old, Kinesis carbon fork on my 2000 Airborne Zeppelin. The carbon connects to aluminum at the dropouts (I think) and the steerer tube / upper fork (pretty sure). It makes me nervious and I'd switch to a metal fork were it not for the fact that I have a stupid, 1" threadless fork and replacements are a bear to source. Because connections are the weak points of structures, I actually feel that my fork would be safer if the steerer tube was carbon too, rather than aluminum. My non-racing self would happily sacrifice half a watt to not have the potential of a catastrophic fork failure gnawing away at me while I ride.

Obviously, this is just one cyclist's opinion. I'm no expert on bike frame construction.


Last edited by Harold74; 09-23-21 at 04:28 PM.
Harold74 is offline  
Old 09-23-21, 06:05 PM
  #78  
Mad Honk 
Senior Member
 
Join Date: May 2019
Location: Bloomington, IN
Posts: 1,852

Bikes: Schwinn Paramounts, Patelli Professional, Othon Ochsner, Masi, Faggin

Mentioned: 54 Post(s)
Tagged: 0 Thread(s)
Quoted: 784 Post(s)
Liked 764 Times in 542 Posts
Harold,
As a golf equipment professional, I daily use an epoxy to bond carbon fiber to metals such as titanium and stainless steel. The ones I use are are high dollar and high shear strength enough that I have yet to test my liability insurance. I'm pretty sure the bike construction folks use similar products to fuse the components together. All of the CF damage I have observed is from impact that is beyond the CF's strength limits. Just my observation, Smiles, MH
Mad Honk is online now  
Old 09-23-21, 06:50 PM
  #79  
Harold74
Senior Member
 
Join Date: Jul 2020
Location: Calgary, AB Canada
Posts: 207

Bikes: 1992 Miyata 1000, 1997 Trek 730, 2001 Airborne Zeppelin, 1980+ Nishiki Olympic

Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 128 Post(s)
Liked 30 Times in 21 Posts
Originally Posted by Mad Honk View Post
Harold,As a golf equipment professional, I daily use an epoxy to bond carbon fiber to metals such as titanium and stainless steel. The ones I use are are high dollar and high shear strength enough that I have yet to test my liability insurance.
Yeah, I saw mention of that earlier in the thread and derived some comfort from it. That said, I'll probe that a little more in the interest of devil's advocacy. I know next to nothing about golf equipment so, if I'm way off base, do let me know.

When I think about the bonding of carbon fiber to metals in golf clubs, the scenario that comes to mind is:

1) A solid shaft as opposed to the hollow tubes used in bicycle frames and;

2) A sleeved connection where in the shaft is embedded substantially into a metallic club head. Again, this is rarely representative of the connections within a bicycle frame.

Both #1 & #2 represent things which I would expect to make the connections within a golf club much less susceptible to failure that connections within a bicycle frame.

How'd I do? Are club shafts really hollow? Are club heads actually made of carbon? Harold does not know...

To the extent that I trust carbon, the thing that gives me the most confidence in it is really just its statistical performance to date which has been alluded to repeatedly above.

I guess the other difference that I see between golf clubs and bicycle frames is the consequences. If I take a swing, hit a rock, and my club head flies off, chances are nobody gets hurt and I just run home to review my warranty paperwork. If my bike fork arm cracks off mid decent, the rest of my life may well be considerably different than it would have been otherwise.

Last edited by Harold74; 09-23-21 at 06:55 PM.
Harold74 is offline  
Old 09-24-21, 05:38 AM
  #80  
Hondo6
Senior Member
 
Join Date: Sep 2021
Location: SW Florida
Posts: 136

Bikes: Yes

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 48 Post(s)
Likes: 0
Liked 45 Times in 30 Posts
Originally Posted by smashndash View Post
hm. Just based off the abstract it seems that I'm talking about translaminar fracture of UD structures under tension. That's probably the closest I'm gonna get to seeing a fatigue test of raw CF.

https://drive.google.com/file/d/1_QX...w?usp=drivesdk

I'm gonna be a pirate and share this for a few days for anyone who's interested. I'll read this in the next couple days and come back if I find anything interesting.
Interesting. Didn't download the article because I had no professional need and thus didn't have the subscription or the need to purchase for mere curiosity. Thanks.

Ran across these and thought you and harold74 (see comments above) might possibly find them of interest. They're quite dated - one is nearly 30 years old, the other 15+ - and I don't really know how much the properties of bare CF itself may have been improved in the interim. Still, they might provide some background info that's useful. Both also seem to require subscription/purchase and/or an account to access the full text.

https://www.sciencedirect.com/scienc...0862239290181U

https://link.springer.com/article/10...837-005-0217-8

Last edited by Hondo6; 09-24-21 at 05:40 AM. Reason: Changed wording for correctness.
Hondo6 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.