Page 35 - Mechanics Analysis Composite Materials

20 Mechanics and analysis of composite materials

Q, MPa

::h-,

0 E, %
0 5 10 15 20 25
Fig. 1.14. Typical stress-strain curves for aluminum (I), magnesium (2), and titanium (3) matrices.

As noted above, metal matrices allow us to increase operational temperatures
for composite structures. Dependencies of longitudinal strength and stiffness of
boron-aluminum unidirectional composite material on temperature corresponding
to experimental results that can be found in Karpinos (1985) and Vasiliev and
Tarnopol’skii (1990) are shown in Fig. 1.15. Naturally, higher temperature
resistance requires higher processing temperature, Tp. Indeed, aluminum matrix
composite materials are processed under Tp=5OO0C, while for magnesium,
titanium, and nickel matrices this temperature is about 8OO0C, 1000°C, and
12OO0C, respectively. Some processes require also rather high pressure (up to
150 MPa).
In polymeric composites, matrix materials play important but secondary role of
holding the fibers in place and providing proper load dispersion in the fibers, while
material strength and stiffness are controlled by the reinforcements. By contrast,
mechanical properties of metal matrix composites are controlled by the matrix to a
considerably larger extent, though fibers still provide the main contribution to
strength and stiffness of the material.

-
,
E, ,GPa 6,MPa

:
loo0 01

400
500
300
100
200
T,o C
Fig. 1.15. Temperature dependence of tensile strength (0) and stiffness (0) along the fibers for
unidirectional boron-aluminum composite.