Page 241 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

220 Chapter 9 Composite Materials: Structure, General Properties, and Applications

TABLE 9.2
Typical Properties of Reinforcing Fibers
Tensile strength Elastic modulus Density
Type (MPa) (GPa) (kg/m3 ) Relative cost
Boron 3500 2600 Highest
Carbon
High strength 3000 1900 Low
High modulus 2000 1900 Low
Glass
E-type 3500 2480 Lowest
S-type 4600 2540 Lowest
Kevlar
29 2800 1440 High
49 2800 1440 High
129 3200 1440 High
Nextel
312 1630 2700 High
610 2770 3960 High
Spectra
900 2270 970 High
1000 2670 970 High
2000 3240 970 High
Alumina (Al2O3) 1900 3900 High
1
Silicon carbide 3500 3200 High
Matrix lg fl Tungsten diameter
Note: These properties vary significantly depending on the material and method of preparation.

L gv-g Kevlar fibers
'yi
i’r"frs

Graphite fibers of 0.012 mm
Boron diameter
5,
0.1 mm
Mali”

(G) (D)

FIGURE 9.4 (a) Cross section of a tennis racket, showing graphite and aramid (Kevlar)
reinforcing fibers. Source: Courtesy of ]. Dvorak, Mercury Marine Corporation; and F. Garrett,
Wilson Sporting Goods Co. (b) Cross section of boron fiber-reinforced composite material.

Carbon Fibers. Carbon fibers (Fig. 9.4a), although more expensive than glass
fibers, have a combination of low density, high strength, and high stiffness; the prod-
uct is called carbon-fiber reinforced plastic (CFRP). Although the words often are
used interchangeably, the difference between carbon and graphite depends on the
purity of the material and the temperature at which it was processed. Carbon fibers
are at least 90% carbon; graphite fibers are usually more than 99% carbon. A typi-
cal carbon fiber contains amorphous (noncrystalline) carbon and graphite (crys-
talline carbon). These fibers are classified by their elastic modulus, which ranges
from 35 to 800 GPa, as lou/, intermediate, high, and 1/ery high modulus. Some trade
names for carbon fibers are Celion and Thornel; see Fig. 9.3.
All carbon fibers are made by pyrolysis of organic precursors, commonly
polyacrylonitrile (PAN) because of its low cost. Rayon and pitch (the residue from