Just how brittle is carbon?

Smokin Joe

Bozman wrote:

Looking at some of the posts and scare stories on here, I'd guess that there's a large skip full of carbon frames after every race day in the pro world. Bunch of ar5e.

I wonder how many people have actually witnessed these "Catastrophic Failures" which cf is prone to after knocking it with your drinks bottle or whatever causes this "Hidden Damage" that only an X Ray machine can detect?

A mate of my brother in law's foreman doesn't count.

FransJacques

Debeli wrote:

This is an odd one. You know that the bicycle is a write-off, but you're not sure whether it's safe to ride.

You can satisfy your curiosity in many ways, but an online cycling forum may not be one of them.

I do not favour carbon fibre on bicycles. I have one or two with cf forks or seat posts, but I prefer steel or alloy for frames.

If you are in doubt, do not ride it. You would not want to be whipping down a steep descent while wondering whether your frame or fork might snap. It would take some of the pleasure out of the experience.

I'm surprised that the money has not been forthcoming. Is there some unsettled issue about the injuries? Six months seems a long time to wait.

But in the meantime, do not ride it until an expert has looked at it - unless you are sure it really is just a scratch or two... and then why is it a write-off?

Steel's the thing. Plastic is for toys.

Oh great one of these guys.

I love you guys. Please don't go away.

gweeds

Debeli wrote:

Steel's the thing. Plastic is for toys.

These posts are comedy gold.

Ignorance is truly a wonderful thing to behold.

Thank God aluminium can't suffer from catastrophic failure. Oh, hang on.....

tangled_metal

For those who know so much about Carbon Fibre. Carbon fibre is a composite of Carbon fibres (stronger than steel in tension) and a matrix of the resin. Carbon fibre is strong in tension along the fibre but can snap easily across the fibre. As you will know it is laid up in layers with each layer the fibre is in a different orientation. You can also get a weave of carbon fibre. It is the way the laminate is made up that gives it a strength in the directions it is designed to. It is a really good material to design where you get the needed strength.

It is light but that is solely due to it's high strength. Think about it, if a material is stronger you use less of it and it becomes lighter. Look at how Titanium is lighter for the same role as steel. It is not a lighter material (higher density IIRC), just stronger so the wall thickness is less than with steel so it is lighter. Aluminium is a lower density but not as strong so has to be thicker to achieve a required strength.

Carbon fibre is a ceramic so is prone to catastrophic failure as mentioned previously. What is that? Basically it is where flaws and weaknesses such as cracks combine and these cracks grow beyond a critical length and grow in size exponentially. That is seen by a carbon fibre strut or pole suddenly snapping.

Quality of carbon fibre is also critical. His torically as the automotive and aerospace industries started to use more and more carbon fibre composites they vacuumed up all the best quality of carbon fibre leaving potentially questionable quality product for other industries. I tend to think a lot of the prejudices of carbon fibre as a somehow inferior material stemmed from then. I think in a lot of the minor industries the carbon was not a good product, especially as they were kind of learning to use it for their applications. I know that at one time carbon fibre trekking poles had a really bad reputation but are now quite common for those into their gear. I guess this is the same for bikes.

Nowadays the carbon fibre industry has grown and more and more players producing quality carbon fibre in volumes able to support the whole range of industries using it. It has also become cheaper due to the increases in volume as larger industries used it more and more (such as in planes). This has spread to the benefits of better quality carbon fibre being used in minor industries like bikes.

The main worry for the OP is what state is the carbon composite. You will not see the internal flaws that may have combined within the material without some form of NDT being done. Just because it does not have cracks showing on the surface or a chip in it or the resin it is safe. You just can not tell. A LBS will not be able to do that. They will probably say it is a write off. I would tend to agree and let the insurance sort it out. It will give you a new bright and shiny to buy from the LBS afterall.

tangled_metal

Sorry about the long post but I had a lot of things to say, more was not said.

One more thing, strong carbon fibre composite components are used in F1 safety compartment because it does not deform but is very strong at a lower weight than other materials. It will be laid up in all directions (the fibre that is) to gain strength no matter where the force comes from. You do not want a safety cell to collapse squashing the occupant. The rest of the car deforms and smashes to slow the car down keeping the occupant safe. It is all about using material in the best way for the intended use. BTW carbon will be used in different ways elsewhere so that it does deform or fails as designed when needed to. That is the beauty of carbon fibre, the designability to meet a varied set of needs.

Normal cars are built to a price point. If that allows carbon fibre and it is the best material to be used it will be used. If not then others are used. That is not to say it is not as good just because we are not all driving carbon monocoques. Also other materials have their advantages too. I would look up a series of books by Ashby if you are interested in material selection. It is a fascinating subject, how we choose our materials for each application.

One more thing, i got told over and again that you can only go so far with designing a product (i.e. designing the shape, construction, etc.) before you run out of gains, that is when materials come into play. Big gains can be made by changing the material but using the same sorts of designs. Then you can start re-designing it to make better use of the new material. SImply put but it is clearly demonstrated with the likes of "buckminster fullerenes" decades ago and more recently Graphene. We are still learning how to implement the Graphene material form into useful products that are able to reach the wider public.

andy_s_t

Cyclum wrote:

Thanks all. That's really helpful.

To fill in a few gaps...

I reported it to the police who took the witness details and went round to speak to her. She admitted liability - that's never been in question.

The driver thought that should be it (she didn't like that the police were involved) and didn't think that it should be reported to her insurance company. I had to nudge her and it got a bit nasty (her). At that point I instructed a solicitor so I could keep out of it. I'm not a member of BC or any other helpful membership (I've learnt the hard way) so I found a solicitor that specialised in cycle accidents... Or so I thought.

They've been pretty rubbish and from what I can gather I'n not actually getting legal advice, simply someone who passes messages between me and the insurance company.

An example - I spent hours photographing my damaged bike, clothing etc, providing receipts for it all... And sent it all to my solicitor. A couple of weeks later I had a message from my 'case handler' to say that they had lost any evidence of purchase and so we're offering an insultingly low figure on the basis that they were calculating it on the assumption that it was a few years old and subject to wear and tear (most was actually only a couple of weeks old). My case handler asked if I was prepared to accept that. I then had to go back and suggest that the receipts were resent to the insurance company. And so it goes on...

I understand that the injury part is treated separately so I should get something for the bike before sorting my knee out. In theory.

And to think I went with them because in my first conversation they talked bikes and told me that "they make it their priority to get you back on the road..." which is actually quite a big deal for me as I don't drive so that is my transport - I don't really have an alternative.

From what I can see your 'solicitors' aren't worth anything and may be the reason that the insurance company are giving low ball offers, remember they are going to have to pay the solicitors fees as well as your medical and bike bills etc.

I got knocked off last year. I spoke to his insurance company direct, they were very helpful. I took my bike to a reputable (Leisure Lakes) bike shop for a quote to fix it, took pics of my damaged helmet and screen grabs of the model to show price etc, and sent these through direct. They paid all in full within a couple of weeks and also gave me a sum for personal injury. The interesting thing I found out was that the insurance company are liable for all your medical bills, ambulance if required, x-rays, the works. They are charged these direct as they inform the health service etc that they were caused as part of an accident.

Can you bin the 'solicitors' and sort it yourself? At least that way you know that something is happening.

rower63

MountainMonster wrote:

...and people give up with the myths that it is going to break if a fly flies into it sideways.

going into it sideways will only end up as a glancing blow, very unlikely any damage done. It's when a fly hits the frame head-on that the real damage gets done

MountainMonster

rower63 wrote:

MountainMonster wrote:

...and people give up with the myths that it is going to break if a fly flies into it sideways.

going into it sideways will only end up as a glancing blow, very unlikely any damage done. It's when a fly hits the frame head-on that the real damage gets done

Ah yes, fly bullets down the frame. Those have crippled many a peleton leaders.

FransJacques

Tangled Metal wrote:

For those who know so much about Carbon Fibre. Carbon fibre is a composite of Carbon fibres (stronger than steel in tension) and a matrix of the resin. Carbon fibre is strong in tension along the fibre but can snap easily across the fibre.

It is light but that is solely due to it's high strength. Think about it, if a material is stronger you use less of it and it becomes lighter. Look at how Titanium is lighter for the same role as steel. It is not a lighter material (higher density IIRC), just stronger so the wall thickness is less than with steel so it is lighter. Aluminium is a lower density but not as strong so has to be thicker to achieve a required strength.

Carbon is a ceramic...???

His torically as the automotive and aerospace industries started to use more and more carbon fibre composites they vacuumed up all the best quality of carbon fibre leaving potentially questionable quality product for other industries. Nowadays the carbon fibre industry has grown and more and more players producing quality carbon fibre in volumes able to support the whole range of industries using it. It has also become cheaper due to the increases in volume as larger industries used it more and more (such as in planes).

Wow dude you're all over the place.

Is there enough carbon or not?
It Ti denser or less dense than steel?

The concepts you discuss are the right ones but your facts are way off. Git edjumicated: http://www.ibiscycles.com/support/techn ... advantage/

And no, carbon is not a ceramic, it's a composite.

tangled_metal

The fibres are sometimes considered a ceramic, IIRC to do with failure types or the carbon based crystals in the microstructure. When you add in a matrix then it's a composite. Without the matrix it's not composite. Of course if I'd said carbon fibre (missed the fibre bit off) the most people think of the composite.

You are right about titanium, blame that on brain freeze. I knew it was denser than aluminium but went to far with the density by saying more than steel. Basically true when comparing it with Al. Blame it on 20 odd years since studying materials and not working in the field. Amazed I've forgotten so much mind you I was more involved in aluminium.

I believe I said that nowadays there are more players in the field producing quality cf able to support the industries using it. Put simply now enough good c.f. but wasn't the case once. Plus different production methods results in cf with different properties/performance. Produced from PAN it's higher strength, but the other main method it's higher Young's modulus. All adds up to an interesting material to use and design in.

My inept attempts to counter earlier posts detracting from carbon fibre composites strengths and weaknesses probably haven't helped. I just find some comments about carbon fibre composites implying it's fragile or unsuitable for bikes is not right. It's a material with it's benefits and weaknesses just like any other. I guess there's a similar question about titanium I think in the popular knowledge/thinking - fatigue being the weakness.

FransJacques

I too have heard that the Airbus R380 hovered up a lot of carbon and there was a limited supply of some materials in some quantities, but I suspect the big factories like Giant and Merida have a decent supply chain and don't necessarily suffer from such fluctuations. Plus I believe that was 5-6 years ago when the R380 assembly line was working overtime to catch up with orders.

I think a lot of the stories of "25 years ago the materials in this bike frame were aimed at Russia" are just marketing bumf. Or "this sh!t is military grade man", whatevs.

Totally agree with you that people don't get carbon. Coming from a sailing background I'm used to seeing how far carbon masts, booms and certainly spinnaker poles can bend before they break, and the knocks they can take in unintended planes. Also, they're much more mendable than Alu. All you need is some pre-preg mat, some expoxy, clingfilm to wrap it all tightly, and a hair drier to set it. You see this happening in sailing club parking lots all over the country after a windy day. OK you might not trust your repaired sprit like you would a new one but at least you can sail the next day.