Composites are materials consisting of a com-bination of high-strength stiff fibers embedded in a common matrix (binder) material; for example, graphite fibers and epoxy resin. Composite structures are made of a number of fiber and epoxy resin laminates. These laminates can number from 2 to greater than 50, and are generally bonded to a substructure such as aluminum or nonmetallic honeycomb. The much stiffer fibers of graphite, boron, and Kevlar epoxies have given com-posite materials structural properties superior to the metal alloys they have replaced.

The use of composites is not new. Fiber glass, for example, has been used for some time in various aircraft components. However, the term application for naval aircraft.

Composite materials are replacing and supplementing metallic materials in various aircraft structural components. The first materials were used with laminated fiber glass radomes and helicopter rotor blades. In recent years, the replacement of metallic materials with more advanced composite materials has rapidly accelerated. This has become particularly evident with the advent of the F/A-18, AV-8B, SH-60B, and CH-53E aircraft; and it is anticipated that composite materials will continue to comprise much of the structure in future aircraft. As a result, there is a growing requirement to train you in the use of advanced composite materials.

There are numerous combinations of composite materials being studied in laboratories and a number of types currently used in the production of aircraft components. Examples of composite materials are as follows: graphite/epoxy, Kevlar/epoxy, boron poly-amide, graphite polyamide, boron-coated boron aluminum, coated boron titanium, boron graphite epoxy hybrid, and boron/epoxy. The trend is toward minimum use of boron/epoxy because of the cost when compared to current generation of graphite/epoxy composites. Composites are attractive structural materials because they provide a high strength/weight ratio and offer design flexibility. In contrast to traditional materials of construction, the properties of these materials can be adjusted to more efficiently match the

requirements of specific applications. However, these materials are highly susceptible to impact damage, and the extent of the damage is difficult to determine visually. Nondestructive inspection (NDI) is required to analyze the extent of damage and the effectiveness of repairs. In addition, repair differs from traditional metallic repair techniques. A more detailed explanation of advanced composites and their inspection and repair procedures are covered in chapter 14 of this TRAMAN.