We've gotten used to new technology that comes along and renders obsolete the old tech it displaces. But there are also plenty of instances where the new meshes nicely with the old, changing the world in amazing and unforeseen ways.
That's what I thought when I stumbled across an article from BusinessWeek about a five-employee startup company in Maine called Advanced Infrastructure Technologies (AIT). This outfit unites innovative new materials with one of humanity's hoariest engineering accomplishments: the construction of the arched bridge.
Specifically, the company has designed a system that allows for the building of a new bridge in as few as 10 days, with no heavy equipment involved. What's more, these structures—because they offer greater protection from corrosive factors like weather and salt—are projected to have a longer life than those made with traditional construction techniques. Although materials are a bit costlier, that's more than offset by savings in labor.
AIT's technique involves using concrete-filled, carbon fiber-reinforced polymer composite tubes.
Many people probably still think of carbon as the stuff that makes up the human body or the end of a graphite pencil, or what is left over after you burn paper. OK, most know that it also makes diamonds. But turning it into a fiber that's strong enough to replace steel in bridge arches? That doesn't seem possible.
Yet it is. Here's how the process—"Bridge in a Backpack," as it's known—works:
Whether AIT will be able to convince a sizeable chunk of the notoriously conservative construction industry that this is in fact a better approach remains to be seen. But so far, it has been involved in the construction of 13 bridges, mostly in Maine, Massachusetts, and Michigan.
In any event, the unlikely image of bridge supports made out of fiber got me to wondering just what other uses there might be for this miracle material. I knew that my golf club shafts use it, for example, and that it's in some car parts which used to be metal. But where else do we find it? Well, turns out that it's just about everywhere.
First, though, just what is it anyway?
Carbon fiber, or CF, is a material made up of carbon atoms bonded together in crystals along the long axis into filaments about 5-10 μm (micrometers) in diameter. This is what one such filament looks like; it's laid atop a human hair for comparison purposes.
CF is possible because of one of the peculiarities of carbon is that it can exist in a number of different forms (allotropes), depending on the way the atoms bond together. Each of these allotropes—which can be fashioned by nature into coal and by man into buckyballs and nanotubes—will have very different properties.
For example, each carbon atom in a diamond is covalently bonded to four other carbons in a tetrahedron. These tetrahedrons together form a three-dimensional network of six-membered carbon rings.
Graphite, on the other hand, consists of sheets of carbon atoms ("graphene" sheets) arranged in a regular hexagonal pattern.
The structure of CF is similar to graphite, with the difference being in the way the graphene sheets interlock.
One surprising fact is that while carbon fibers are generally thought of as a space-age material, their lineage actually dates back to the late 1800s. Thomas Edison used carbon fibers in his early light bulb filaments, which required the ability to conduct electricity while remaining fire resistant and capable of enduring the intense heat needed to create incandescence.
In order to make the fibers, you start with a raw material, or precursor. Edison took a cellulose-based precursor such as bamboo and baked it at high temperature in a controlled atmosphere in a carbonization process known as "pyrolysys." It's similar to what we still do today.
The technology took a long time to evolve. Bamboo and other such materials were not replaced as precursors until the introduction of rayon into the process in the late 1950s. That yielded the first high-tensile-strength fibers. Shortly thereafter, in the early 1960s, modern CF arrived with the discovery that polyacrylonitrile, derived from petroleum, was the ideal precursor. However, this early manufacturing process produced a fiber that was only 55% carbon.
At present, polyacrylonitrile is still the source of 90% of the world's carbon fiber, but purification has improved dramatically, with standardization of quality coming in 1990. The precursor is now stretched into long strands, and then heated to a very high temperature without allowing it to come in contact with oxygen. Without oxygen, the fiber cannot burn. Instead, the high temperature causes the atoms to vibrate violently until most of the non-carbon atoms are expelled. This method of carbonization leaves a fiber that's nearly 100% carbon.
Carbon fibers are relatively expensive when compared to similar products such as glass or plastic fibers, due to the manufacturing process being slow and energy intensive. But their properties—high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance, and low thermal expansion—make them desirable for particular applications, especially when combined with resins and molded. (If perchance you have some DIY home projects that might benefit from carbon fiber molding, you can have a go at it, beginning with this tutorial.)
That is to say, CF by itself is an interesting material, but alone it's of little value in structural applications. What really kicked its usage into high gear was what happened when it was added to different kinds of resins to create composites, generally termed "carbon-fiber-reinforced polymers" (CFRPs).
You may remember the first composite tennis racquets, which revolutionized the game in the early 1980s. And as soon as they could, golfers of a certain age began choosing carbon fiber (usually mischaracterized as "graphite") shafts instead of steel for their clubs, because the former are more forgiving and much easier on older bodies.
Even before that, though, governmental and private aerospace efforts had been quick to embrace the possibilities. Carbon fiber composites' favorable strength-to-weight ratio means weight savings of 20-30% over heavier metals. Thus it began to replace steel and aluminum—wherever possible consistent with safety—in airplanes and helicopters… a godsend for the Air Force. But commercial interests weren't far behind. Weight reduction is everything in the airline business. A modern jet aircraft is apt to have carbon fiber all over the place: in its fairings, landing gear, engine cowls, rudder, elevators, flaps, fin boxes, doors, floorboards, and many other components.
Much the same happened in extraterrestrial craft. CF has gone into space with NASA and on to the moon. Again, weight considerations are paramount when lifting off from the earth. But equally important is a lower ablation rate (i.e., the speed at which a material is stripped away by the friction of reentry), along with higher bulk density, superior mechanical strength, and high modulus (inelasticity). Carbon fiber composites—including carbon-carbon, which consists of CF-reinforced graphite—that have been densified fill the bill, and are used in nose tips and heat shields.
The space shuttle was largely dependent on CF materials. CF/epoxy composites made up the payload bay doors and the shuttle's remote manipulator arm. Likewise for satellites, which require high specific stiffness and dimensional stability to combat the large temperature swings in space. Thus similar composites are employed in fabricating antenna ribs and struts.
Lately, there has also been much publicity about unmanned aerial vehicles (UAVs), or drones, as they are more commonly called. UAV bodies are likely to be made of CF materials. So are the gondolas and tail fins used in blimps.
But carbon fiber is not only found in such esoteric arenas. It's very much a part of the more grounded aspects of life. For example:
- Race cars—The sport has used the tech to create faster cars with lighter bodies. Among NASCAR and Formula 1 race cars, each of them has a body constructed from carbon fiber composites.
- Street wheels—While the cost of CF bodies for cars has put them beyond the reach of ordinary consumers (i.e., those who can't afford Lamborghinis), that's about to change. CF's properties make it ideal for electrics, where lighter weight means longer distances between battery charges. BMW plans to be first to market with its electric city car, the i3, slated for release in 2014. Despite the higher cost of a CF body structure, the company will realize savings in the water and electricity needed to make it; thus the i3 will be marketed for about the same cost as conventional 3 Series models. BMW concedes the risk involved, but chances are it will not be the last company to make this leap.
- Sporting goods—We've already mentioned tennis racquets and golf clubs. But that's just the beginning. CF has also become an integral part of such products as sailboats, rowing shells, canoes, bicycles, motorcycles, tripods, fishing rods, hockey sticks, paintball equipment, archery shafts, tent poles, protective helmets, pole vaulting poles, and pool cues. Shoe manufacturers use carbon fiber as a shank plate in some basketball sneakers to keep the foot stable.
- Music—Increasingly, CF is finding its way into such things as drum shells, bagpipes, and stringed instrument bodies. It also goes into high-end audio loudspeakers, and musical accessories such as violin bows and guitar pickguards.
- Building retrofits—CFRP can be applied to enhance shear strength of reinforced concrete by wrapping fabrics or fibers around the section to be strengthened. Wrapping a building column can also improve its ductility, greatly increasing the resistance to collapse under earthquake loading. Such seismic retrofit is a major and very cost-effective application in earthquake-prone areas, since it is much more economic than alternative methods. The use of ultra-high modulus CFRP is also one of the few practical methods of strengthening cast-iron beams, to which it can be bonded.
- Infrastructure—Prestressed concrete cylinder pipes (PCCP) account for the vast majority of water transmission mains in the US. But they are prone to corrosion and gradual deterioration. Failures of PCCP are usually catastrophic and affect large populations. But over the past decade, CFRPs have been utilized to line PCCPs internally, resulting in a strengthened structural system. Inside a PCCP, the CFRP liner acts as a barrier that controls the level of strain experienced by the steel cylinder in the host pipe. The composite liner enables the steel cylinder to perform within its elastic range to ensure the pipeline's long-term performance is maintained.
- Medicine—The poster boy (at least, before his arrest on suspicion of murdering his girlfriend) for carbon fiber prosthetics was South Africa's Oscar Pistorius, who ran in the Olympics on his CF legs.
- Weapons—CF can substitute for metal, wood, and fiberglass in many areas of a firearm in order to reduce overall weight. Carbon fiber is also a popular material in crafting the handles of high-end knives.
- Other consumer products (with the caveat that many of these currently are expensive vanity items)—These include such things as wallets, money clips, belts, corkscrew bodies, organizer trays, iPhone cases, license plate frames, attachés and briefcases, laptop stands, duffle bags, sunglass and eyeglass frames, toilet seats, luxury bathtubs, coffee tables, table lamps, pens, sushi plates, and, yes, cigar cutters.
All of this merely scratches the surface.
The fact of the matter is that carbon fiber has in a relatively short time become an integral part of modern life. New applications are popping up literally on literally a daily basis. Usage is expected to drive a $13+ billion/year business by 2015. That figure will be amplified a great deal as cheaper, more efficient manufacturing techniques are developed.
If carbon fibers were suddenly to disappear, we'd be up the proverbial creek without a (CF) paddle…
[Doug Hornig is a senior editor for Casey Extraordinary Technology.]