Page 246 - Manufacturing Engineering and Technology - Kalpakjian, Serope : Schmid, Steven R.

Section 9.4 Applications of Reinforced Plastics 22

modulus, EC, of the composite can be calculated by replacing 0 in Eq. (9.3) with E.
Thus,
EC = xEf + (1 - x)E,,,. (9.5)

EXAMPLE 9.I Calculation of Stiffness of a Composite and Load Supported by Fibers

Assume that a graphite-epoxy reinforced plastic with Because
longitudinal fibers contains 20% graphite fibers. The
Pf
elastic modulus of the fibers is 300 GPa, and that of PC = Pf+ Pm and Pm = Begg,
the epoxy matrix is 100 GPa. Calculate the elastic
modulus of the composite and the fraction of the We obtain,
load supported by the fibers.
Pf
P, = Pf + % = 2.33Pf, or Pf = 0.43Pc.
Solution The data given are x = 0.2, Ey = 300 GPa,
and Em = 100 GPa. Using Eq. (9.5),
Thus, the fibers support 43% of the load, even
E, = 0.2(300) + (1 - o.2)1o0 though they occupy only 20% of the cross-sectional
= 60 + 80 = 140 GPa. area (and hence volume) of the composite.
From Eq. (9.4), the load fraction Pf/Pm is found to be
Yi; I 5 = 0.75.
0.2(300)
Pf

9.4 Applications of Reinforced Plastics

The first engineering application of reinforced plastics was in 1907 for an acid-
resistant tank made of a phenolic resin with asbestos fibers. In the 1920s, formica, a
trade name, was developed and used commonly for countertops. Epoxies first were
used as a matrix material in the 1930s. Beginning in the 1940s, boats were made
with fiberglass, and reinforced plastics were used for aircraft, electrical equipment,
and sporting goods. Major developments in composites began in the 1970s, result-
ing in materials that are now called advanced composites. Glass or carbon fiber-
reinforced hybrid plastics are available for high-temperature applications, with
continuous use ranging up to about 300°C.
Reinforced plastics typically are used in commercial and military aircraft,
rocket components, helicopter blades, automobile bodies, leaf springs, driveshafts,
pipes, ladders, pressure vessels, sporting goods, helmets, boat hulls, and various
other structures and components. The Boeing 777 is made of about 9% composites
by total weight; that proportion is triple the composite content of previous Boeing
transport aircraft. The fuselage of the new Boeing 787 Dreamliner is made of com-
posites, for reduced weight and higher fatigue resistance.
By virtue of the resulting Weight savings, reinforced plastics have reduced
fuel consumption by about 2%. The newly designed Airbus jumbo jet A380, with a
capacity of 550 to 700 passengers, has horizontal stabilizers, ailerons, Wing boxes
and leading edges, secondary mounting brackets of the fuselage, and a deck structure
made of composites with carbon fibers, thermosetting resins, and thermoplastics.
The upper fuselage will be made of alternating layers of aluminum and glass fiber-
reinforced epoxy prepregs.
The hood of the 2008 Mustang automobile is made of a carbon-fiber com-
posite. The contoured frame of the Stealth bomber is fashioned out of composites