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OVERVIEW OF COMPOSITE MATERIALS 1 Theodore J. Reinhart 1.1 INTRODUCTION Composite materials are macroscopic combi- nations of two or more distinct materials having a discrete and recognizable interface separating them. Thus composites are hetero- geneous materials, and many are naturally occurring; the most common is wood. The composites of interest in this discussion, how- ever, are the synthetic, man-made materials, possessing high strength and/or stiffness rela- tive to weight which are used in high performance structural applications because of these properties. Figure 1.1 shows the strength- and stiffness-to-weight relationships for several fibers when arrayed in unidirec- tional laminates. The narrower definition of composites becomes more specific and can be restricted to those combinations of materials that contain high strength/stiffness fiber reinforcements supported by a high performance matrix material. Fibers and matrix materials may be organic or inorganic in chemical make up. Normally the fibrous reinforcement material is referred to as the discontinuous phase and the matrix material as the continuous phase. The primary engineering properties of the composite are derived predominantly from the mechanical and physical properties of the discontinuous phase, the fiber reinforcement. These are the fiber-dominated properties of the composite. Increasing the fiber volume Handbook of Composites. Edited by S.T. Peters. Published in 1998 by Chapman & Hall, London. ISBN 0 412 54020 7 fraction results in increases in the levels of mechanical properties up to the point where there is insufficient matrix material to support the fibers and to transfer load within the com- posite. The matrix is the adhesive binder that supports the fibers under compressive loads, provides shear capabilities in two dimensional fiber lay-ups, and transfers loads internally in the composite among the myriad fibers and fiber bundles that comprise the load-carrying portions of the composite material. In two- dimensional composites the matrix provides the basic resistance to impact damage and delamination. Fig. Plot of specific tensile strength to specific tensile modulus for commercially available com- posites.
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22 Overview of composite materials Matrix materials may be selected from metallic, ceramic and organic resin materials. With perhaps the exception of ceramic matrix composites, the matrix material is not as strong or as stiff as the discontinuous phase or fiber material. There are many exceptions or perhaps special cases to these statements. Many organic resin matrix materials are mod- ified to increase toughness by the addition of small amounts of rubber base or thermoplastic modifiers, thus forming a discontinuous phase of particles within the continuous matrix phase of the composite. The classes of fiber- reinforced composites are usually related to the form of the fibrous reinforcing material and include continuous, long discontinuous and short discontinuous fiber-reinforced com- posites. Complicating the straightforward
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This note was uploaded on 03/16/2010 for the course MECHANICAL ME765401 taught by Professor Prof.sulis during the Spring '10 term at Institut Teknologi Bandung.

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