Callister - An introduction - 8th edition

16.13 Processing of Fiber-Reinforced Composites • 659
Figure 16.14
Schematic diagram
illustrating the
production of
prepreg tape using a
thermoset polymer.
Doctor
blade
Hopper containing
heated resin
Release
paper
Waste release
paper
Spooled
fiber
Carrier
paper
Heated calender
rolls
Spooled
prepreg
At room temperature the thermoset matrix undergoes curing reactions; therefore,
the prepreg is stored at 0C (32F) or lower. Also, the time in use at room temperature
(or out-time) must be minimized. If properly handled, thermoset prepregs
have a lifetime of at least six months and usually longer.
Both thermoplastic and thermosetting resins are used; carbon, glass, and aramid
fibers are the common reinforcements.
Actual fabrication begins with the lay-up—laying of the prepreg tape onto a
tooled surface. Normally a number of plies are laid up (after removal from the carrier
backing paper) to provide the desired thickness. The lay-up arrangement may
be unidirectional, but more often the fiber orientation is alternated to produce a
cross-ply or angle-ply laminate. Final curing is accomplished by the simultaneous
application of heat and pressure.
The lay-up procedure may be carried out entirely by hand (hand lay-up), wherein
the operator both cuts the lengths of tape and then positions them in the desired orientation
on the tooled surface. Alternately, tape patterns may be machine cut, then
hand laid. Fabrication costs can be further reduced by automation of prepreg lay-up
and other manufacturing procedures (e.g., filament winding, as discussed next), which
virtually eliminates the need for hand labor. These automated methods are essential
for many applications of composite materials to be cost effective.
Filament Winding
Filament winding is a process by which continuous reinforcing fibers are accurately
positioned in a predetermined pattern to form a hollow (usually cylindrical) shape.
The fibers, either as individual strands or as tows, are first fed through a resin bath
and then are continuously wound onto a mandrel, usually using automated winding
equipment (Figure 16.15). After the appropriate number of layers have been
applied, curing is carried out either in an oven or at room temperature, after which
the mandrel is removed.As an alternative, narrow and thin prepregs (i.e., tow pregs)
10 mm or less in width may be filament wound.
Various winding patterns are possible (i.e., circumferential, helical, and polar)
to give the desired mechanical characteristics. Filament-wound parts have very high
strength-to-weight ratios. Also, a high degree of control over winding uniformity