Carbon Fiber for the Common Man
by David Surace
“A group of Japanese companies which control 70% of the global carbon fiber market want to increase the usage of carbon fiber in automobiles.”
You see, carbon fiber–or if we’re picking nits, carbon-fiber-reinforced-plastic, a material with the strength of steel at only 1/3 the weight–is certainly no stranger to the automobile, as our man Bruce McCulloch covered around this time last year. But right now the lion’s share of the material still goes to large aircraft manufacture, specifically airliners, where the fuel savings more than make up for carbon fiber’s stratospheric cost and slow manufacturing time.
In an automobile, which is several orders of magnitude smaller, less expensive and quicker to build, the return-on-investment argument for carbon fiber is harder for the average consumer to swallow. So for right now, it’s still the preserve of supercars, F1 paddocks and high-performance toilet seats.
But what if it wasn’t? What if it became the ho-hum everyday composite for everyone? And what would replace it?
Let’s address the first question: according to the interesting Automotive News article (subscription req’d) which Mr. Tan sources, the big carbon fiber manufacturers in Japan, Toray Industries, Teijin and Mitsubishi Rayon, have plans up their sleeves to increase production of the material and, in turn, cut the exorbitant cost to the consumer. And, in turn, make gobs of money.
Now, for those of you who only have vague ideas about what carbon fiber is, I invite you to think of it like reinforced concrete. The tiny carbon strands (about 6 micrometers thick) are woven together in a matrix similar to the steel rebar used to erect your local Wal Mart. Those strands serve to spread weight or force across the entire body of the structure, instead of gathering it at a single weak point. Then you can add a liquid element which can harden; in Wal Mart’s case it’s concrete, and in carbon fiber’s case it’s plastic resin or epoxy. Whereas concrete hardens in the sun, the epoxy must be baked in a very hot oven called an autoclave in order to stiffen up.
With the multiple pieces all smooshed together, a lot of people like to call the resulting material a “composite”, kind of like a composition is simply a body of work (like an opera, or a term paper) made of many parts.
If you can imagine every Wal Mart being built out of solid blocks of travertine stone like the Colosseum in Rome, you can see why the steel rebar & concrete combination has been so popular.
But if it’s like rebar then why is it so bloody expensive? For starters there’s the carbon strand itself: you begin the process with individual fibers of a very nice material called Polyacrylonitrile (the “acrylic” content of your t-shirt is made out of this same material), then burn it to within an inch of its life. If you cooked it right, the end result is about 55% pure carbon, and those carbon atoms excitedly arrange themselves into a very efficient hexagonal pattern called a graphene sheet. In tubular form, this is now your carbon strand, anxiously waiting to be made into a toilet seat.
One of the really neat things about this material is that, depending on how you weave the carbon fibers, the composite material can either bear loads in all directions (omni-directional), or it can hold up against stress coming from only one direction. Formula One teams often use the “uni-directional” material to make delicate control arms and suspension pieces, which bear most of their stress in side-to-side or up-and-down motions.
But an F1 car is clearly a cost-no-object application. The challenge for Japan’s automotive carbon-fiber players is to make it a value-added proposition over the already trustworthy steel and aluminum alloys. Fortunately for them, however, your daily driver doesn’t have to endure nearly the amount of stress of an F1 car on day-to-day basis.
So why not make the strands out of a less stringent material for, say, non-structural parts? Scientists are already experimenting with recipes for Short Fiber Reinforced Polymer, a material which uses some “split ends” of acrylonitrile carbon fiber strands, usually blown in at odd angles to create an interlacing effect before the resin material is poured in. This material is not nearly as strong as woven carbon fiber, and would never be mistaken for an “advanced” composite, but with the help of an old friend, glass fiber, you can make what is essentially a re-re-reinforced fiberglass.
What about fibers made of things other than acrylic? For years experiments have been underway to determine a suitable (and petroleum-free) successor to acrylonitrile, one that perhaps might even yield a higher concentration of carbon atoms per strand, from natural fiber extracts like cotton, hemp, sisal and curaua all the way up to metal fibers made of highly-elastic aluminum alloys. The goal is to find a reinforcing material that’s easier, greener, faster and cheaper.
Or how about reinforcing your composites with something that isn’t a fiber at all, but a clay? Great minds in materials engineering have also been plugging away at so-called nanoclay composites, a class of reinforced plastic that uses ultra-fine particles of a natural clay called montmorillonite, a fine, powdery, almost greasy-feeling clay originally discovered in the eastern French town of Montmorillon. Like the graphene sheets that carbon atoms like to form, the alumina and silica molecules in clay minerals also like to form orderly shapes, using their shared oxygen atoms to form corners in a linked tetrahedral shape. These guys then lock together with other clay-making molecules to form rigid sheets.
Sounds far fetched? There’s already a company bringing these things to light: PolyOne Corp., an plastics manufacturer out of Avon Lake, OH is already playing with montmorillonite-infused polymers which are strong enough and stiff enough to stand up on their own as an automotive body application.
Going just a little further, you could imagine an automotive paint process that only involves one or two super-thin layers of nanoclay-reinforced primer and colorant, followed by one single layer of “self-healing” clearcoat. On top of being tougher and reacting to scratches by bursting tiny nanocapsules full of “clearcoat” resin, the weight savings over a traditional automotive paintjob (which typically involves between 4-10 coats) could be significant.
While those things are cooking, however, carbon fiber’s meticulous manufacturing process should become faster, easier, and more open-source (as of right now, carbon weave processes are still fiercely kept a trade secret). So perhaps by the time my (unborn) children are in the market for a minivan, the once-exotic carbon weave will have gone out of style–and come back again.
Postscript: If you’re still thirsty for more information about Fiber-Reinforced Composites, there’s a very good synopsis from the Engineering Fundamentals website available HERE.
COPYRIGHT Autosavant – All Rights Reserved