Composite Basics Six. / Andrew C. Marshall

'Composite' is a general term which means an assembly of dissimilar rnaterials used together to enable them to do a job that the individual materials cannot do by themselves. Under this definition, even reinforced concrete is a composite. 'Advanced composites' refers to that group of materials usually associated with military or commercial aerospace structures and using the newer materials. They are carefully engineered and developed, and are uniquely suited to carrying substantial loads in structural members which have surprisingly light weight. These materials usually consist of a resin matrix-typically an epoxy, polycyanate, poiyester, or vinyl ester-and a fiber reinforcement. The fiber reinforcement can be glass, Keviar, carbón fiber, Nextel, quartz, boron, or any of a number of other fibers all of which are very small in diameter and very strong, ünparting a high degree of strength to the resulting mixture. This added strength is so large that the performance of a composite as a structure is usually another order of magnitud e when compared to the strength of the resins by themselves. Even so, the strength and stiffness of the resin matrix does affect the finished composite structure, and stronger resins, such as epoxies, usually yield a higher strength structure than one which employs a lower strength resin, such as a general purpose poiyester.