Man's evolution has been tied to his progress in materials. Yesterday it was the Stone, Bronze and Iron Ages. Today it is the Age of Composites. However, even in these earlier ages man experimented with and learned to use composite materials. This is evidenced by the Israelites' use of chopped straw in their brick; the Egyptian sarcophagi fashioned from glued and laminated wood veneer and also their use of cloth tape soaked in resin for mummy embalming; the Mongol warriors' high-performance, recurved archery bows of bullock tendon, horn, bamboo strips, silk and pine resin, which are 80% as strong as our modern fiberglass bows; Chinese bamboo rockets reinforced with rope wrappings; Japanese Samurai swords formed by the repeated folding of a steel bar back on itself; the early fabrication of steel and of iron gun barrels in Damascus; and the Roman artisans' use of ground marble in their lime plaster, frescoes and pozzolanic mortar. The ancients also used goat hair in their clay for the fabrication of pottery which, after firing, was converted to a form of carbon, the forerunner of modern carbon fiber reinforced ceramics.
The Challenges
The first challenge in writing this dictionary was to provide the interested technologist with a comprehensive lexicon and source of information about the many key facets, as well as common, new and unfamiliar terminology associated with composites. The second challenge was what to include in the text.
Although this text is called a dictionary, it is somewhat of a hybrid because in many instances the entries may appear similar to those in an encyclopedia. The content is a natural reflection of the author's background, training, experience and interest. The mechanical engineer would tend to favor the aspects of design, engineering and testing, while the polymer chemist/scientist might lean toward the chemistry, molecular engineering, synthesis, formulation and analysis. Thus, one needs to strike a balance between the many and allied disciplines of composites and the desire to be comprehensive and yet concise.
The Compromise
This leads us to the compromise of what constitutes a composite. There is no universally accepted definition for a composite material. Any definition is at best imprecise and may or may not include materials considered by some to be composites.
The purist considers a composite to consist of two or more identifiable constituents which just about includes everything except homogeneous or single phase materials. The other extreme is the group that believes composite materials do not include sandwiches, laminates, felts, etc., but consist only of a continuous matrix phase that surrounds the reinforcing phase structure.
There also are those who differentiate between a composite material and a composite structure such as safety glass or other laminates.
Others classify composites into microcomposites, which include reinforced and toughened thermoplastics, sheet molding compounds and metallic alloys; and macrocomposites, which include reinforced concrete, galvanized steel and helicopter blades.
Still another author does not accept natural composites such as wood or bone because they do "not have a structure of arbitrary variation."
Any definition of a composite material is also at best a compromise. Too narrow and rigid definition of a composite will restrict the type and number of entries. The following is the one chosen after deliberation:
Composite A multiphase material formed from a combination of materials which differ in composition or form, remain bonded together, and retain their identities and properties. Composites maintain an interface between components and act in concert to provide improved specific or synergistic characteristics not obtainable by any of the original components acting alone. Composites include: (1) fibrous (composed of fibers, and usually in a matrix), (2) laminar (layers of materials), (3) particulate (composed of particles or flakes, usually in a matrix), and (4) hybrid (combinations of any of the above).
The definition will allow the inclusion of natural materials such as wood which consists of cellulose fibers bonded together with lignin and other carbohydrate constituents, as well as the silk fiber spun by a spider which is as strong as steel on a weight basis consisting of a gel core encased in a solid protein structure as composite materials.
Laminated safety glass can be considered a composite material in that the glass needs the safety-net effect of the polyvinylbutyral interlayer, if impacted. The interlayer requires durability and rigidity for normal useful service.
Included in the composite umbrella definition are cermets, concrete, asphalt, plywood, tires, plasterboard and even some fibers such as graphite and boron. The graphite fibers can be considered composites because only part of the carbon has been converted to graphite in tiny crystalline platelets specifically orientated to the fiber axis, while the boron fibers are not strictly fibers, but are composites consisting of a thin layer of boron coating over a tungsten or carbon substrate.
The multilayer high-oxygen barrier plastics thermoformed from a six-layer barrier sheet is a composite material. More difficult to accept as composite materials are galvanized steel, consisting of a coating of layers of zinc which yields a corrosion resistant product with the strength of steel, and the solid golf ball, containing only polybutadiene rubber reinforced with silica pigment and tightly cured.
Clearly the distinction between different types is unclear when we consider the broad spectrum of composite materials from the specialized unique metal matrix composites to the lowly vinyl-reinforced garden hose.
Efforts have been made to employ SI units in the cited definitions. However, in some instances established procedures, tests, and conventional and trade use prefer obsolete units such as inches, mils, psi, denier, angstrom, calorie, micron, poise, cubic, etc.
Reference sources for the reader's perusal are included [1-24].
Words in small capital letters indicate that further relevant or comparative information is provided in a separate entry. Undefined entries are set in italics.
We are especially indebted to ASM International, The American Society for Testing Materials, T/C Press, Think Composites, VNR Publishing Company, Pegleg Books and Technomic Publishing Co., Inc. for granting permission to use selected definitions.
I wish to acknowledge the support of the late George Lubin, my friend and a long-time member of the SAMPE Journal Editorial Board. I also would like to thank Kier Finlayson for his acute and diligent editorial assistance.
References
1. ASTM Committee on Terminology, Compilation of ASTM Standard Definitions, ASTM (1986).
2. Bennett, H., ed. Concise Chemical and Technical Dictionary, Chemical Publishing Co. (1986).
3. Billmeyer, F. W., Jr. Textbook of Polymer Science, John Wiley (1984).
4. Bower, C. M. Composite Materials Glossary, T/C Press (1985).
5. Cheremisinoff, N. P. and P. N. Chenemisinoff. Fiberglass Reinforced Plastics Deskbook, Technomic Publishing Co., Inc. (1978).
6. Cowan, H. J. and P. R. Smith. Dictionary of Architectural and Building Technology. Elsevier Applied Science (1986).
7. Definitions Committee of the Federation of Societies for Coatings Technology, Paint/Coatings Dictionary, Federation of Societies for Coatings Technology (1978).
8. Grayson, M., ed. Encyclopedia of Composites, John Wiley (1983).
9. Guide to Materials Engineering Data and Information, ASM International (1986).
10. Hartshorn, S. R., ed. Structural Adhesives, Chemistry and Technology, Plenum Press (1986).
11. Hull, D. An Introduction to Composite Materials, Cambridge University Press (1981).
12. Lubin, G., ed. Handbook of Composites, VNR Publishing (1982).
13. Margolis, J. M., ed. Advanced Thermoset Composites, Industrial and Commercial Applications, VNR Publishing (1986).
14. Ptirker, S. P., ed. McGraw Hill Dictionary of Chemical Terms, McGraw Hill (1985).
15. Pethrick, R. A. and G. E. Zaikov, eds. Polymer Yearbook-3, Har-wood Academic (1986).
16. Sax, N. I. and R. J. Lewis, Sr. Hawley's Condensed Chemical Dictionary, llth Ed., VNR Publishing (1987).
17. Sheldon, R- P. Composite Polymeric Materials, Applied Science (1982).
18. Southworth, J. Aerospace Vehicle Structures, An Expanded Glossary of Terms, Principles, and Methods, Pegleg Books, Burbank, CA (1986).
19. Tsai, S. W. Composite Design, Think Composites (1986).
20. Veilleux, F. F., ed. Dictionary of Manufacturing Terms, SME (1987).
21. Weeton, J. W., D. M. Peters and K. L. Thomas. Engineers Guide to Composite Materials, ASM International (1987).
22. Whittington, L. R. Whittington's Dictionary of Plastics, Technomic Publishing Co., Inc. (1978).
23. ASM Metals Reference Book, American Society for Metals (1981).
24. Stuart, D. M. Manual of Aerospace Composites, Volume 1: Details, A.A.C. Publishing Company, Wichita, KS (1982).
Stuart M. Lee
Palo Alto, California
Copyright ©1989 Technomic Publishing Company, Inc. All rights reserved.