Carbon Fibre - perceived issues

[apache]

Obviously in relation to bikes.

The frequent 'will they or won't they break' threads regarding Spinergy wheels has piqued my interest.

Now, from peripheral experience of composites via the military and commercial aviation industry, I know that there is nothing at all wrong with the material when used correctly in suitable applications. However, I wonder if certain cycle businesses have been market driven rather that application driven regarding the use of CF in bicycles.

It's easy to imagine marketing people seeing CF being used in civil and military aviation back in the 80s, and suggesting it as a panacea for bicycle parts. Lighter, stronger and very cool!

However... a large part of CF's strength comes from the design rather than the material itself. The Spinergy wheels, to my limited experience of CF (though 28 years of experience in military tech / engineering) just look 'wrong' in that they seem to be designed to the strengths of an alloy wheel. In other words, they don't appear to play to the strengths of CF - monocoque construction in particular, like the tri-spoke 'Spin' wheels do.

It's a bit like forming CF into tubes and bonding them together to form a conventional 'triangles' bike frame - it's treating CF like steel. It doesn't have the same properties or failure modes as steel, but in the rush to get a big glitzy CF bike into a manufacturers range of bikes and suck in the consumer, proper design and dare I say safety take a back seat to profit.

 

[jamswinna]

The forces applied to bicycle frames is pretty universal, and the double diamond design has proved its safety and strength over decades of use with almost every material one can think of from a manufacturing point (metals, textiles, woods etc) - using a different/ new material dosen't always command a design change i guess???

 

[hamster]

Much of the reason for 'bike shaped' CF frames is the UCI, which effectively banned other forms.

The reason that the Burrows/Lotus bike that Chris Boardman rode to the world hour record became a dead end was the UCI.

But I agree, much is also consumer reluctance to buy a non-bike-shaped bike also.

 

[Barneyballbags]

Early CF bikes and bits were sketchy to say the least. Some were very good, some were appaling. I think the early days were as much about trial and error as anything else, as a lot of manufacturers probably didn't fully know how their CF products would hold up, and a lot of early CF bits didn't hold up very well at all!

This lead to the whole "will it or won't it break" syndrome, and people were quite rightly concerned about CF, and weren't very confident in using it.

Look at modern bikes, however, and it's a completely different story. Steve Peat rides a carbon fibre V10 with lots of carbon bits, and he's doing alright

If done properly, there's no reason why a carbon bike can't be lighter, stiffer AND stronger than it's metal equivalents.

 

[Ollytron]

I was amazed last night when ready a copy of mtb UK after not seeing a copy for 10 years at how much cf is used now, they even do the crank arms.out of it.

 

[mikee]

a lot of problems in early days of c/f came from the bonding of other parts to it , short shelf lives of adhesive's and subsequent de-bonding
a bit like welding metal, the areas pertaining to the join being the usual problem
i have a few carbon bikes that seem to be holding up well dispite thier years tho they dont get the level of use or abuse that threatens them

 

[apache]

So, CF failures and lack of confidence in CF components in the early years are likely due to lack of understanding of the properties of CF on the part of the bicycle manufacturers, and a rush to get the latest bling to market.

This is understandable given that the people who were building with CF had $billion R&D budgets and were properly set up to test the results (Boeing, General Dynamics are two I remember) - this doesn't excuse the rush to bring sub-standard parts to market though does it?

I don't pretend to understand in detail the stresses in a bike wheel, though its easy to picture in the case of the Spinergy wheel, a very obvious failure mode. CF doesn't tend to be good in compression, and given that CF fails suddenly rather than deforms first, it's easy to understand potential for catastrophic failure. This is also why I don't see it being a suitable material for 'copying' the double diamond frame. Why not play to the materials advantages rather than sticking with a sub-optimal design?

I appreciate the UCI comment by the way. Is that still a current rule?

I also appreciate that CF has come a long way, and todays components and bicycles are likely to be as strong as any other material. However, I have noticed one or two CF components with rider weight limits on them!

Interestingly, the 'flutter' failure put forward for the wheel in question, if true, smacks of poor design. CF can be built to not flutter at all, hence it's use in the first 'successful' forward swept winged aircraft - the Grumman X-29. Forward sweep tends to induce flutter from the tips inwards, whereas conventional sweep tends to naturally damp flutter. The Germans had flutter problems with their aluminium designs.

 

[kingoffootball]

I decided I needed to research carbon fibre and other fibres, like boron, in regards to bike frames last month, and found this article very informative:

http://www.calfeedesign.com/tech-papers ... ite-paper/

A lot of it is probably stuff you know, if you know a reasonable amount about carbon fibre anyway, but I thought I'd post it.

 

[hkind]

I have worked in a composite R&D shop and have made several items out of various epoxy and fibre combinations. I have also had the chance to find the failure point on composite products Composites are great for some applications but not MTB's, in my opinion.

I still have a NOS Kestrel MXZ F/F. Thought it would be a waste to build something I did not trust.

 

[apache]

Is that painted, or is it some other weird composite - like man made granite??