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Carbon Fiber
by Jonathan Buhalis

Description

Carbon the element takes many forms, including coal and diamond. Carbon fiber is a strong and lightweight but expensive material woven from carbon thread. Carbon-fiber-reinforced-polymer (CFRP), the more common commercial product, is a composite material of carbon fiber in a reinforcing matrix such as epoxy.

Carbon can form strong sheets, which is a crystalline form called graphite. Thin carbon tubes used in CFRP may be thought of as graphite sheets rolled up in one direction. These tubes are manufactured in one of two ways. A carbon-rich substance like tar may be laid down in the desired geometry, or a carbon polymer such as rayon may be manipulated into tube form. In either case, the starting material is baked to drive off any element except carbon. Heat also coaxes the carbon atoms into their natural crystalline linkage.

Thousands of carbon tubes (diameter 5 microns) are woven into a carbon thread. This thread has very high tensile strength. It is stored on bobbins and can be woven into fabrics.

carbon fiber cylinder, A. Jonathan BuhalisA CFRP is a carbon fiber fabric molded into some desired shape, then painted with or encased in a hard plastic such as epoxy. A CFRP sheet or rod is much stronger by weight than steel (right). It has high stiffness or tensile strength, depending on how it was formed. It may tolerate very high temperatures.

Drawbacks

Carbon fiber thread and CFRPs are expensive and used where performance or weight has a high priority over cost. CFRPs can be fragile vs. cuts and impacts depending on the matrix polymer.

Metal sheets and rods have an elastic range within which they can bend again and again without deforming. Carbon fibers do not have a reliable elastic range and can fail over time.

Applications

carbon-fiber bike, A. Jonathan BuhalisCarbon fiber and CFRPs are very common in high-end sports equipment. Most hand-held sports gear is available as carbon fiber, including tennis racquets, golf clubs, hockey sticks, and fishing rods. Bicycle frames (right), racing shells, kite spars, surf boards, and arrows are available as carbon.

Racing cars employ CFRPs in constructing their chassis and other components where possible. Some high-end commercial cars use carbon-fiber body panels.

Boeing 787 Dreamliner, A. Jonathan BuhalisCommercial aircraft are beginning to emerge constructed with carbon fibers. The Boeing Dreamliner (right) and the Airbus A350 XWB are among the first. These are among the largest aircraft. The smallest aircraft, including ultralights and tiny unmanned drones, also use CFRPs.

In civil engineering, sheets of carbon fiber can be used to wrap concrete columns and spans. The sheets provide compression strength and sheer strength. Sheets can be added after compression and are the favorite choice for earthquake retrofitting.

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Content by Jonathan Buhalis
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