Boeing 787 Dreamliner - Mark Wagner [37]
But modern composite materials in aerospace traced their origins well back beyond Airbus and Boeing to the late 1950s, when the Cold War was at its height. The United States was concerned that its intercontinental ballistic missiles (ICBMs) could be intercepted, and decided that higher reentry vehicle speeds were needed to guarantee delivery of their deadly nuclear payloads. However, higher reentry speeds meant higher temperatures, and a new material was needed to withstand the thermal shock. Research produced a ceramic/metal composite called Avcoite to do the job, and it was successfully tested on the U.S. Air Force’s new Minuteman ICBM. Carbon fibers also were developed at about the same period as reinforcements for high-temperature molded plastic parts on shorter-range missiles.
These first types of carbon fibers were made by heating strands of rayon until they turned into carbon. However, as the carbon content was only about 20 percent, they were relatively weak, and it was not until the 1960s, when the carbon content was boosted to about 50 percent by the use of a new raw material called polyacrylonitrile, that the first true potential of carbon fiber could be glimpsed.
A composite structure consists of fibers held together in some form of matrix, or glue. A tree, for example, is a composite structure because it is made up of cellulose fibers bonded together by lignin. A graphite or carbon composite similarly consists of carbon fibers consolidated together with a tough resin.
The individual carbon fibers are long, very thin strands about 0.0002 to 0.0004 inch (0.005 to 0.010mm) in diameter and composed mostly of carbon atoms bonded together in crystals. These turn out to be amazingly strong for their size because their microscopic structures are roughly aligned parallel to the long axis of the fiber. Twisted into a yarn, thousands of these fibers are combined to make a fabric that is then mixed with an epoxy, or glue, and wound or molded into whatever shape is required.
Although the strength and lightness of the carbon material had obvious appeal for aerospace, in these early years it was too expensive to use because of the low production volumes involved. It was the sports industry that came to the rescue, jump-starting production of carbon materials for use in golf club shafts, fishing rods, and tennis rackets. The sporting material of choice at the time was mainly graphite fiber, which has an internal structure close to that of graphite, a pure form of carbon. Boron filament reinforced epoxy also became widely used in sports equipment, although this was generally more expensive.
Although invar, an iron-nickel alloy, was the preferred material used for making large composite tools because of its controlled coefficient of thermal expansion, lighter mandrels better suited to lean manufacturing also were sought for the 787. Janicki Industries, a local yacht builder based in Seedro-Wooley, Washington, helped Boeing develop new mandrel technology. Spirit AeroSystems meanwhile selected bismaleimide (BMI), a high-temperature composite material from Cytec, for its mandrels, while others, such as Alenia, stuck with invar. Here the end of an invar mandrel is glimpsed inside the newly formed Section 46 center fuselage at Alenia’s Grottaglie site. Mark Wagner
The later 1960s also saw the introduction of higher-strength carbon and aramid fibers, as well as better “prepregs,” a term for the fabric or tape made from the fibers already