11 Description

1.1.1 Scope

Polymer composites can cover a broad range of material combinations. For this chapter, we will consider those combinations that are between the stages of those still being invented and those in wide use. We will also restrict our consideration to those combinations that are intended for structural application. Many, if not most, of the basic concepts and principles of use will be applicable across the total range of materials developed. The specific characteristics of the materials discussed or used as examples will be of those that are advanced in the sense that their full use potential has not yet been realized. For that reason, a great deal of attention will be given to those material combinations that incorporate continuous carbon or graphite fibers as a reinforcing material in a high-performance polymer matrix. Unlike many metals, polymer composite formulas are often proprietary to their suppliers. Contact the supplier to determine the best polymer composite for your application. Suppliers can be identified by contacting the Composite Fabricators Association at www.cfa-hq.org. They are located at 1010 North Glebe Road, Suite 450, Arlington, VA 22201, telephone 703-525-0511.

1.1.2 History and Future Developments

Modern polymer composites can trace their origins back to the 1950s when researchers at Wright-Patterson Air Force Base in Ohio began to investigate the properties of plastics that had within them embedded glass fibers. The motivation for these investigations was the search for materials that would meet the ever-increasing demands for higher performance aircraft. Lighter, stronger, and stiffer were the guiding principles. In conjunction with companies such as Owens-Corning Fiberglas and Union Carbide, a high-performance composite of continuous S-Glass and epoxy was developed. This composite found applications in such places as the Poseidon missile casing and ballistic armor. It is still an important material today.

In the 1960s, fibers composed of oriented carbon or graphite began to be developed. The fibers were of low density and higher stiffness than glass fiber. As the demands of agencies such as the Air Force and National Aeronautics and Space Administration (NASA) grew for higher stiffness materials than metal or glass fiber composites, these carbon/graphite fibers and their composites became the materials of choice. Today, many consider advanced composites to be those reinforced with carbon or graphite fiber. In actuality, glass-fiber-reinforced composites continue to find new, advanced uses. The design, manufacturing, testing, and performance measuring methods for polymer composites containing any fiber were developed during the time when glass-reinforced composites were finding expanded usage.

The history of glass and carbon-fiber-reinforced composite development is documented by several authors. It is not the intent here to review that history beyond the simple introduction given above. It needs to be pointed out, however, that the composites developed as a result of the search for stiffer, lighter, stronger has had some fortunate side effects in other areas. The new materials also gave the designers more choices of materials for their electrical, thermal, and corrosion needs. These nonstructural properties will be further explored later in the chapter.

The future of polymer composite development is mixed. The decade of the 1990s has seen a slowdown in the drive for improvements led by aerospace. Companies that competed with each other in the need to produce ever more advanced products have seen the market drastically change. Performance used to be the differentiating factor. In today's world, performance with affordability or value is the key. The industry is looking for new customers in application areas that were not even imagined when advanced polymer composites were developed. Golf clubs, tennis rackets, hockey sticks, softball bats, pole vault poles, canoes, fishing poles, and the like are but the tip of the iceberg for new applications. Automobile, truck cab and trailer, railroad car, and ship applications are under active development. The success of these applications will depend upon designers embracing these materials in their work.

As inventors and applications engineers begin to be comfortable with the type and nature of these advanced materials, application areas will expand and costs will come down. It is hoped that this chapter will give to the designer the basic knowledge and understanding of how these material work, how they are made, and, most importantly, how they can open design imagination.

1.1.3 Definition

Stating a simple definition of a composite is a deceptively complex task. It gets even more difficult if the definition is intended to convey the multitude of options available. Here are a few examples:

1. Made up of distinct parts or elements

2. A macroscopic combination of two or more distinct materials, having a recognizable interface between them

3. Two or more materials judiciously combined, usually with the intent of achieving better results than can be obtained by using individual materials by themselves

4. High-strength fiber—primarily continuous, oriented carbon, aramid, or glass rather than randomly distributed chopped fibers or whiskers—in a binding matrix that enhances stiffness, chemical and hydroscopic resistance, and pro-cessability properties

Each of these definitions is equally correct. They express an increasing degree of complexity to the product being defined. They also imply the ability (or difficulty) to define a material simultaneously with its application. Engineered materials, as they are often called, now require the designer to consider materials other than those available to him in the "handbook." The material he will use is now his to define, as he needs. This material will be made from parts and elements put together in a manner chosen to best fulfill the need. The possibilities are immense; the solutions only limited by imagination.

Baseball For Boys

Baseball For Boys

Since World War II, there has been a tremendous change in the makeup and direction of kid baseball, as it is called. Adults, showing an unprecedented interest in the activity, have initiated and developed programs in thousands of towns across the United States programs that providebr wholesome recreation for millions of youngsters and are often a source of pride and joy to the community in which they exist.

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