Good sources of information on carbon fiber

[Mark Davison]

I've been looking for reliable sources of information on carbon fiber composites. I'm look for sources that are publicly available and not hidden behind paywalls.

The wikipedia article on Carbon fiber reinforced polymers seems reasonable:

https://en.wikipedia.org/wiki/Carbon...orced_polymers

Are there any composite material experts on the Paceline who can verify the article and/or suggest alternate information sources? Is there a standard textbook in the field?

One thing I like about the wikipedia article is that it makes it clear that the material properties of the composite are very different than the properties of the constituents.

[Mark Davison]

Change "look" to "looking" in the previous post.

[AngryScientist]

You do realize that they make everything from wind turbine blades to piston connecting rods to sidi soles out of carbon fiber, yes?

You're going to have to narrow down what you want to learn to get more useful suggestions, IMO.

(and you can edit your own posts, fyi)

[prototoast]

If you do a Google Scholar search, there is a lot of academic research on carbon fiber that is free to access, though not always the most layperson friendly.

[Carbonita]

Here's the material science textbook I used back in the 80's. Short section on fiber reinforced plastics. I recall using prePreg to lay up test coupons, and the care needed to avoid resin pockets and voids to achieve good properties on the hydraulic rig. Pretty impressive bang at failure!

[Mark Davison]

Originally Posted by AngryScientist

You do realize that they make everything from wind turbine blades to piston connecting rods to sidi soles out of carbon fiber, yes?

You're going to have to narrow down what you want to learn to get more useful suggestions, IMO.

(and you can edit your own posts, fyi)

Yes, I realize that CFRP is used to make many things, including submersibles that implode, seat posts that fail completely, leaving sharp jagged ends, steer tubes that crack when stem clamps are overtightened, handlebars that crack after impact loads that aluminum bars would have survived.

I'm looking for background information to allow me to make my own judgements about how suitable CFRP components are for my own bicycling activities and maintenance routines, independent of marketing claims.

The internet is full of extravagant, passionate and unsupported claims on all sides of this issue.

I suspect, but do not know and cannot prove, that the practical questions may come down to how much safety margin is designed into a given component, and unfortunately this may not be information that a consumer has access to.

Just as a concrete example: I truly love the functionality of my Specialized Diverge with its CFRP frame. But I don't currently have a bike carrier for my car roof rack that I feel is safe with the Diverge. In order to accommodate fenders, I am using a Thule rack that allows you to leave the wheels on, and clamps the down tube. Thule makes a pad which they claim makes the clamp safe for a CFRP frame, but I don't intuitively trust it. In order to keep the bike secure against vibration you have to apply quite a bit of force when you clamp it.

I suppose I could source a fork clamp bike carrier that accommodates the disk brakes on the Diverge, and just live with removing the front fender.



And thanks for the tip on editing posts.

[Dude]

Yeah, we're going to need specifics - even then "we" can't really give you an answer. You're asking "how do I eat" when really you want to know how much baking soda you need for toll house cookies.

When it comes to specifically knowing if you can use that dt holder on a rack, I'd call both the rack manufacturer (which you did) and also specialized. Know whatever they tell you won't stand up legally if a gust blows your bike and it cracks. There is probably like, 2 people in all of specialized who actually know the clamping force required to squish that part of the downtube.

The other other option is to a different roof rack carrier - in this case a fork mount - that will hold your bike and not interfere with the fenders.

[rice rocket]

Why not just reach out to Specialized and ask?

They have engineers on payroll that know what their products are and aren't designed to do.

[Carbonita]

You're correct in your concern with loads that are not used in the design of the structure, which is the frame in this instance. Failure prediction is difficult even when design load is applied. I recall a design competition which required us to FEM a design for a cantilever structure, predict the failure mode (buckling, fracture, elongation, etc.) and magnitude, and have the best strength to weight ratio constrained by budget. Students came into the test with varied designs of Aluminum, CFRP, and spruce, in models using truss, stressed skin, plates. Many failure predictions were off by a factor of two. Causes for unexpected failures were due to joint construction, material variance, and lack of concentrated load distribution.Now add in non intended loads, as with a clamped bike frame at an arbitrary location, and it's a truly difficult problem

Originally Posted by Mark Davison

I'm looking for background information to allow me to make my own judgements about how suitable CFRP components are for my own bicycling activities and maintenance routines, independent of marketing claims.

The internet is full of extravagant, passionate and unsupported claims on all sides of this issue.

I suspect, but do not know and cannot prove, that the practical questions may come down to how much safety margin is designed into a given component, and unfortunately this may not be information that a consumer has access to.

Just as a concrete example: I truly love the functionality of my Specialized Diverge with its CFRP frame. But I don't currently have a bike carrier for my car roof rack that I feel is safe with the Diverge. In order to accommodate fenders, I am using a Thule rack that allows you to leave the wheels on, and clamps the down tube. Thule makes a pad which they claim makes the clamp safe for a CFRP frame, but I don't intuitively trust it. In order to keep the bike secure against vibration you have to apply quite a bit of force when you ...

[Mike Lopez]

40+ year industry veteran in composites here. Currently building tomorrow's
space junk but spent decades designing, testing, and manufacturing composite bicycle components. Reynolds Composites founder, Serotta, Action Composites, etc.

With all respect Mark, it sounds as if you've already drawn your own conclusions so I'm not sure what further internet propaganda may be able to tell you. Most of what you'll find is techie stuff not applicable to the fashion show of the bicycle industry.

What I can say is that the quest for extreme lightweight components at low cost has not helped the durability issue. In the process of designing and testing forks for example I found that roughly an ounce of material in the right spots made the difference between a "adequate" design and a robust design. This was verified through mechanical testing of hundreds of samples in static, dynamic, and impact testing.

I always defaulted to the safety of robust designs but the product managers often said something like "if you can't make it pass at < 300g then don't bother". I generally told them to pack sand and that's why you still see 20+ year old Ouzo Pros & Serotta F3s still performing well and not sending folks to the dentist as the alarmists like to say.

The exception to this was the Reynolds UL which was my final project there before I moved on. I let the product manager have it his way and the rest was history. Adequate v robust. It passed the tests under ideal conditions but in the real world had some issues.

If there are any specific, objective, questions you may have I can try to help answer.

[prototoast]

There's no general answer about carbon fiber that can tell you how much clamping for a particular downtube can support--that depends on the specifics of how the frame was constructed (tube diameter, wall thickness, type of fiber used, layup).

In general, I wouldn't be worried about that situation. I have put a carbon fiber frame I built myself into my friend's rack of that style without concern--but in that case, I knew that my frame was overbuilt.

A carbon frame that weighed as much as a steel frame would be virtually indestructible. But, of course, that's not how most carbon frames are designed. Even something like a carbon hardtail mountain bike frame, which is designed to be quite burly, will typically weigh significantly less than a lightweight steel road frame.

If your diverge is one of the ones with downtube storage, you could measure the wall thickness around the point and that would give you some insights, but you still wouldn't know the fibers or layup.

[KonaSS]

Just stay away from anything carbon fiber. Your posts on the subject have shown that you clearly don't trust it and have a bias against it.

That is fine. Don't use it. Plenty of other alternatives. Your own reasonable doubt is clearly greater than most other peoples, so just go with your gut. You are not going to find a third party internet source that is going to prove to you that your Diverge is safe.

[AngryScientist]

Originally Posted by Mark Davison

Just as a concrete example: I truly love the functionality of my Specialized Diverge with its CFRP frame. But I don't currently have a bike carrier for my car roof rack that I feel is safe with the Diverge.

What is this a concrete example of?

You are certainly not going to find an answer as to whether you can feel comfortable clamping your Spec's DT in a bike rack in technical literature about carbon fiber. There lies the problem. There are no general answers to broad questions about the integrity and durability of carbon fiber as it depends on far too many variables.

This guy's youtube channel is a good place to do some casual research though:

https://www.youtube.com/@LuescherTeknik/videos

[krooj]

Originally Posted by AngryScientist

What is this a concrete example of?

Poor selection in rack; just say NO to roof racks.

[Bob Ross]

Originally Posted by Mike Lopez

Currently building tomorrow's space junk

Thread Drift: @Mike Lopez do you know or did you ever work with Geoff Gould?

I know he started in the composites industry designing satellite antenna masts for the Voyager program. But he's been doing musical instruments (CF bass guitar necks) for the last 4+ decades, which is how I met him.