Carbon Fibre (Fiber) Investment

[Guest625101138]

I can weld steel to get fair results.

I can screw and glue aluminium to get fair results but have problems getting good welds. I need a lot more practice.

My latest materials love affair is with carbon fibre.

I have done a couple of bits and pieces now with CF and am really impressed with the results. The numbers do not mean much until you see something made from it and give it a test.

I used some offcuts of 3mm PVC foam recently to compare fibreglass and CF panels. Photos attached.

The FG is 320gsm cloth and the CF is 200gsm cloth. Both were layed up resin rich to get good coverage with simple pressure layup. I cut the test panels to 400mm by 75mm. The FG one weighs 54g and the CF one weighs 50g. You would expect the CF to be somewhat lighter but the weight is indicative of the excess resin.

The photos are not ideal for showing the deflection but the difference is quite obvious. Actual deflections were 15mm and 35mm for a 5kg load. The pieces were simply supported at 350mm spacing if anyone wants to check the modulus.

So I am really impressed with the stuff. Its elastic modulus is outstanding.

It leads me to a few questions:
1. Is it the material of the future?
2. Is it a means to sequester carbon?
3. Is it overall more energy efficient in say a motor car than steel? (I could imagine building a two person electric car that weighs about 100kg that would perform adequately for town use.)
4. Who is the leading supplier of the raw materials?
5. Who is the leading supplier of the cloth or yarn?
6. If you were looking to make an investment in a company likely to benefit from CF usage what company would you choose?

Rick W

[marshmat]

Hi Rick,

I've built a few solar cars out of CF, and in order to satisfy the marketing dep't and the sponsors, we did have to come up with some answers to a few of your questions. I'll summarize what we found:

1. Is it the material of the future?

It could be, under two conditions. Firstly, a much cheaper and more efficient means of producing carbon fibre is required. Secondly, techniques for the mass production of CF parts would have to be brought to the same level as current steel and plastic production techniques.

2. Is it a means to sequester carbon?

No. It's actually fairly energy-intensive to make, at present. Polyacrylonitrile is probably the most common precursor fibre, but pitch and rayon can also be used. Regardless of which precursor is used, quite a lot of energy is needed to run the multi-stage furnaces (especially the 2,000 deg.C inert-gas furnace stage that induces graphitization). We didn't calculate the GHG emissions from this stage, other than they are probably quite large.

3. Is it overall more energy efficient in say a motor car than steel?

The use of CF does result in a very significant weight savings. The bare carbon body / chassis of a two-person solar car is light enough for one person to pick up (although at 2x6 m, is a bit too bulky to actually do that). This only translates to a more efficient car if the power plant is downsized accordingly. A solar car cruises on about 1 kW and, if drawing the battery down at peak rates, can typically output about 5 kW momentarily. Put a 300hp V8 in a carbon chassis and it'll go like stink, but it won't be much (if any) more efficient than the same engine in a steel body.

Last I checked, there were about half a dozen big suppliers of the stuff - Toray, Cytec, Hexcel, etc. I think Toray's the biggest right now but I don't know by how much, if that's even correct to start with.

Having worked mainly with woven carbon cloths on those projects, I am now of the opinion that a woven cloth is a waste of many of carbon's best properties. If building in this material again, I would try to get stitched multi-axial fabrics. The alternating creases in the yarns of a woven carbon cloth create a lot of stress concentrations, decreasing the material's strength- in some cases by a factor of two. But biax doesn't have the nice weave pattern of twill or satin cloths, and so often doesn't look as appealing to the buyer of the product.

[Guest625101138]

Matt
Thanks for the information. I will shop around for the companies you name.

As far as the car goes I did intend to take full advantage of the weight saving. If you could build the car for under 100kg then Li-ion batteries become commercially viable because you do not need many.

I have also noticed the issue with the weave. The test piece I made did eventually suffer compression failure at the weave line right in the middle. It may have been different with two layers with the weave of each layer slightly offset. THe load to do this though would have made the glass panel into a loop.

Rick W

[jehardiman]

There are a couple of other reasons that carbon is not a wonder material.

It is very sensitive to fiber orientation. One part I know of showed a 50% reduction in strength when the fiber was oriented 7 degrees off axis. To prevent this in production, a CNC fiber laying machine was required.

It is costly compared to FG from a strength point of view. From a cost standpoint in basic design, the improvement is properties don't justify it's use in most marine structures.

It is very hard to repair back to strength. This again is a fiber orientation issue.

Fastening it is difficult because its high modlus leads to point loading and zippering of fasteners.

All that said, CF has a place in the engineers toolbox, but a wrench shouldn't be used like a hammer...one tools does not fit all uses. IMHO, CF is used poorly too often in marine applications and I expect it to be several more years until its "high-tech" shine wears off.

[Guest625101138]

John
I know what mean by the fad "high-tech" users. In fact a good proportion of the uses are decorative. Many avoid coloured coatings so the fabric remains visible. The 12k flat twill I get is about half the price of tighter weaves and has to be used carefully to avoid bunching. The edges have a retaining thread so it falls apart when cut unless it is taped. The best way for me to use it is to form full width flat panels.

For my pedal powered boats the weight is critical. If I can make a boat that weighs 15kg rather than 25kg it is a huge benefit. It is the difference between just slinging it on top of the car rather than a struggle and risk of muscle strain. So CF provides tremendous utility in this regard.

Comparing the two thin panels I made, the fibreglass is like stiff rubber compared with the metal like stiffness of the CF.

I know the motor car industry are looking at ways to speed the moulding process. Somehow I do not believe any are working with a clean slate. I would like to see them start from scratch using the full advantages of the material rather than just some component replacement. I have a fundamental problem with the need for a 2000kg vehicle to transport a 75kg person for most of the distance travelled. Does not make sense.

Rick W

[Jimbo1490]

Basalt is the fiber of the future. With high-end aerospace gobbling up worldwide CF production year after year, CF is just going to stay too pricey for the foreseeable future to trickle down to the average boat. Basalt gives you about 90% of the UTS and about 50% of the stiffness of (regular modulus) CF at a price that's only about double e-glass. It's also less brittle (therefore more damage tolerant) than CF and has superior heat insulating properties. Because of the way CF is made and finished, it's really not suitable for use with polyester resin. Even the companies offering more advanced proprietary finishing systems on their CF textile do not claim compatibility with poly resin, only epoxy, VE and the exotics like bismaleimides. All the other makers use a thin layer of epoxy resin as the textile finish (it's so thin you can't feel it), which explains why it's most compatible with epoxy.

But being a mined and melted/extruded mineral fiber (just like glass) basalt can get the same finishes like Volan and Silane, so you can use any resin you want, like cheap poly. This is important to getting a new raw material product into really widespread use in mass production, and another reason why CF won't wind up in such widespread use. This is the kind of universal adoption that's needed to get prices down.

One disadvantage to basalt is that it mostly comes from Russia, meaning the existing production infrastructure is antiquated and incapable of keeping up with large (western) industrial demand (if such demand ramps up). Couple that with an emerging new 'cold war', and you can see that prospects are not outstandingly good that this will replace e-glass in the near future.

But it could

Jimbo

[Boston]

hey Rick
love the subject mater
dont have time at the moment cause my dinner is burning but
check out carbon tubes
now thats the material of the future
will read all when I get a chance
B

k read through
I was thinking of carbon fiber for my mast and spars on my next project
was going to just use old school sail rings
and was wondering how the abrasion would effect it
I was leaning towards tweed
but now Im not sure
course I dont know jack about carbon fiber so I have a lot of research to do before I buy

[marshmat]

There are some structures based on carbon nanotubes that, if produced in macroscopic quantities, would likely have tensile strength on the order of 100 to 150 GPa (recall that mild steel is 0.4 GPa tensile strength), and elastic modulus around 900 GPa (compare to mild steel at ~200 GPa). I'm not aware of any experimental results to date in which tensile strengths of more than 63 GPa were demonstrated.

Current prices from commercial suppliers are on the order of $250 to $2500 per kilogram for cheap multi-wall tubes, if purchased in quantity, and more like $75,000 per kilogram for single-walled variants. So if anyone wants a building material that starts at a quarter million bucks a tonne for the raw material (not even in macroscopic fibre form yet), be my guest

[jehardiman]

Rick;

As Matt points out, there is a fairly hefty cost to performance benefit. What I did when I used it on a marine HPV was to only use it as the outer (tension) layer over bagged glass. In this way, I got a thin panel with glass as the "core" and the CF as the outer strength core. The same concept applies to "top-hat" stiffeners...lay linear CF as the last layer(s) ast the outermost fiber is the most stressed.

Edit; also remember that CF does nothing for buckling..you will still need the requsite SM to take the compression loads.

[marshmat]

Hi jehardiman,

I've done a few layups in the fashion you describe. Using just a single layer of uni carbon as the outermost skin can be a reasonably economical way to use the stuff to stiffen up an otherwise floppy part.

We did find, though, that when you do this, the failure modes become a fair bit more complicated. The carbon's elongation at break is substantially lower than that of the glass or Kevlar under it. So the panel bends very little, until the carbon fails- and when carbon fails, it does so in a spectacular fashion. Depending on how you've engineered the layers under it, you might get a large but manageable deflection, or you might get a cascade failure layer-by-layer as the layers of successively lower quality fibres are suddenly stressed. One way around this is to also calculate the strength and deflection of the remaining laminate after the carbon has failed, and ensure that even if it deflects excessively, it won't fail before you have a chance to unload it.

Engineering with mixed fibres is not something I would generally recommend unless there's a compelling reason to do so. I've tried it, and it can work, but it's not necessarily straightforward.

[Guest625101138]

Originally Posted by jehardiman

Rick;

As Matt points out, there is a fairly hefty cost to performance benefit. What I did when I used it on a marine HPV was to only use it as the outer (tension) layer over bagged glass. In this way, I got a thin panel with glass as the "core" and the CF as the outer strength core. The same concept applies to "top-hat" stiffeners...lay linear CF as the last layer(s) ast the outermost fiber is the most stressed.

Edit; also remember that CF does nothing for buckling..you will still need the requsite SM to take the compression loads.

John
Those test panels I made were for a boat I am working on now. They have a single layer of cloth either side of the 3mm PVC foam core so one face is seeing compression when being bent. Apart from the eventual collapse of the foam at the line of the weave both CF and FG performed will in compression. This is partly why I am not too worried about a little extra epoxy.

The layup of 200gsm CF either side of 3mm foam is more than adequate for a 20ft hard chine sealed hull I am making. It requires about 4sq.m and the panel comes in at 1.6kg/sq.m. Hence weight of the hull will be around 8kg by the time I join the panels and add some bulkheads.

I have already made two 6ft long outriggers and they come in at 1.4kg each. The drive frame, including full-back recumbent seat, is 2.2kg. All these parts were made from the same layup with selective stiffening. So I will get close to achieving target weight of 15kg.

Originally I intended on making the new boat out of 320gsm FG and 6mm corecell as I could get good prices on a 100m roll of the FG cloth but after making the test pieces and doing the comparison I decided the CF was much better even though somewhat more expensive. I pay AUD35/sq.m for the CF compared with AUD8.2/sq.m for the FG in quantity.

My current 24ft boat has a 10" wide deck of 320gsm FG on the 3mm foam and it is decidedly "soggy" under load. It really needs midpoint support. The CF will be much stiffer.

Rick W

[Boston]

I was dreaming of carbon nanotubes
I dont think they are commercially available anywhere yet

molecular tubes of carbon chains
it has some interesting properties
I have a paper round here some were on it
if any one is interested
but it may be outdated as I think I got it from a few years ago
B

[Guest625101138]

Matt
I looked at share performance of the three you suggested, Toray, Cytec, Hexcel and they have followed market trends. Hexcel maybe even worse. I guess their fortunes right now are tied to aircraft and high tech toys so these will not be selling well.

Where do you buy your CF and how much do you pay if that is not confidential?

Also where do you get you Solar cells for the solar cars?

Do you ever get to Australia for the Solar Challenge? I think it is the oldest of the solar races.

Rick W

[venomousbird]

Carbon nanotubes cost something on the order of thousands of dollars a gram, and they have exotic properties that probably mean big brother won't want petty civillians playing around with them anytime soon. Interestingly enough, they form naturally in tiny quantities in a simple campfire, but the process for sorting them out goes right over my head at the moment.

As far as carbon fiber, it shouldn't actually be so darned expensive at all. I see the shortage and expense as a technological bottleneck, the man keeping us down sorta thing. It's just yarn heated up to a few thousand degrees in an inert atmosphere.

To produce them, I propose a closed box, with an inert gas being released slowly into it to maintain pressure above that of the surrounding atmosphere, with a reel-to-reel type mechanism pulling yarn slowly through it, and a laser (or lasers) focused on the rayon yarn as it passes through.

[venomousbird]

I've seen the price for carbon fiber quoted at $80 Canadian for a one yard by 50 inch sheet. Pricey stuff unfortunately.