Over the past quarter century, substantial advances have been made in the aerospace applications of composites. The designs of modern aircraft, particularly military fighter aircraft, demand high-strength, high-stiffness, low-weight materials. While multiphase composite materials of various kinds have been used for centuries, the development in the last 40 years of high-stiffness continuous fibers, either of graphite or glass, has changed the picture for aerospace materials. Coupled with reliable interfacial chemistry at the fiber-matrix interface and advanced epoxies and thermoplastics, composite laminates began appearing in high-performance aircraft around 1970. The boron-epoxy speed brake on the McDonnell-Douglas F-15A was one of the first such applications. With better control of the graphitizing process, high-stiffness, micron-sized carbon fibers began making their appearance composite form. These fibrous composite laminates have fulfilled the demand for ever stiffer and lighter materials, but not without some disadvantages. Fiber-epoxy laminates have a well-known sensitivity to impact damage and degradation due to environmental factors, such as ultraviolet light and moisture. Additionally, the cost of producing and maintaining fiber-epoxy laminates is very high. In order for combat aircraft to meet their performance objectives, these limitations must be accommodated. Military transport and commercial aircraft, however, are much more cost-sensitive and must be economically maintainable.
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