Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-15 GTBL042-Callister-v2 August 29, 2007 8:52

648 • Chapter 15 / Composites

Pullers

Fiber

rovings

Preforming

die

Resin

impregnation

tank

Curing

die

Figure 15.13 Schematic diagram showing the pultrusion process.

15.13 PROCESSING OF FIBER-REINFORCED

COMPOSITES

To fabricate continuous fiber-reinforced plastics that meet design specifications, the

fibers should be uniformly distributed within the plastic matrix and, in most instances,

all oriented in virtually the same direction. In this section several techniques (pultru-

sion, filament winding, and prepreg production processes) by which useful products

of these materials are manufactured will be discussed.

Pultrusion

Pultrusionis used for the manufacture of components having continuous lengths and

a constant cross-sectional shape (i.e., rods, tubes, beams, etc.). With this technique,

illustrated schematically in Figure 15.13, continuous fiberrovings,ortows,^3 are first

impregnated with a thermosetting resin; these are then pulled through a steel die

that preforms to the desired shape and also establishes the resin/fiber ratio. The

stock then passes through a curing die that is precision machined so as to impart the

final shape; this die is also heated to initiate curing of the resin matrix. A pulling

device draws the stock through the dies and also determines the production speed.

Tubes and hollow sections are made possible by using center mandrels or inserted

hollow cores. Principal reinforcements are glass, carbon, and aramid fibers, normally

added in concentrations between 40 and 70 vol%. Commonly used matrix materials

include polyesters, vinyl esters, and epoxy resins.

Pultrusion is a continuous process that is easily automated; production rates are

relatively high, making it very cost effective. Furthermore, a wide variety of shapes

are possible, and there is really no practical limit to the length of stock that may be

manufactured.

Prepreg Production Processes

prepreg Prepregis the composite industry’s term for continuous fiber reinforcement preim-

pregnated with a polymer resin that is only partially cured. This material is delivered

in tape form to the manufacturer, who then directly molds and fully cures the prod-

uct without having to add any resin. It is probably the composite material form most

widely used for structural applications.

(^3) A roving, or tow, is a loose and untwisted bundle of continuous fibers that are drawn
together as parallel strands.