12 Constituent Materials And Properties

The materials that make up the parts of a composite are usually referred to as the constituents. For a polymer composite, the two basic parts are the polymer matrix, or resin system, and the fiber reinforcement. In the next section, the options available for each of these two parts will be presented along with some specialized intermediate forms of product that form the starting point in the design of a structure made from a polymer composite.

1.2.1 Fibers

Polymer composites have developed into important structural materials due to the wide variety of reinforcing fibers that are available. Glass and carbon fibers are by far the most common types and are produced by a number of manufacturers worldwide. Other fiber materials such as aramid, quartz, boron, ceramic, or polyethylene are also available and provide unique properties. For applications in advanced polymer composites, the most common form of the fiber is continuous tow (carbon) or roving (glass). In this form, continuous filaments have been gathered as untwisted bundles and packaged in spool form. Typically, these packages weigh between 2 and 20 lb and are supplied on 11 by 3-in. cores. This product is the basic element for further processing (either directly or via intermediate forms) into a polymer composite structure.

Carbon fibers were first commercially produced from a regenerated cellulose fiber (rayon). Because of high production costs and environmental concerns, rayon-based carbon fiber is not widely used today. The majority of carbon fiber available today is made from an acrylic precursor fiber (polyacrylonitrile, or PAN) and is the most commonly used structural fiber. Fibers made from petroleum or coal tar pitch are also available and, because of their high modulus and unique thermal properties, find uses in thermal management applications. PAN-based carbon fibers are available from a number of sources. Tables 1.1, 1.2, and 1.3 present typical properties of carbon fiber products. The tables are grouped by tensile modulus grade; low or standard (33-35 Msi), intermediate (40-50 Msi), and high (>50 Msi).

Today, new fiber developments are producing material with heavier tow count and lower costs. These materials are usually of the low modulus type and will find applications in high-volume applications such as automotive, construction, and infrastructure.

TABLE 1.1 Low Modulus (<275 GPA) Carbon Fibers
0 0

Post a comment