Page 25 - Mechanics Analysis Composite Materials

10 Mechanics and analysis of composite materials
1.2.1. Fibers for advanced composites

Continuous glass fibers (the first type of fibers used in advanced composites) are
made by pulling molten glass (at a temperature about 1300°C) through 0.8-3.0 mm
diameter dies and further high-speed stretching to a diameter of 3-19 pm. Usually
glass fibers have solid circular cross sections. However there exist fibers with
rectangular (square or plane), triangular, and hexagonal cross sections, as well as
hollow circular fibers. Typical mechanical characteristics and density of glass fibers
are listed in Table 1.1, while typical stress-strain diagram is shown in Fig. 1.7.
Important properties of glass fibers as components of advanced composites for
engineering applications are their high strength which is maintained in humid
environments but degrades under elevated temperatures (see Fig. 1.8), relatively
low stiffness (about 40% of the stiffness of steel), high chemical and biological
resistance, and low cost. Being actually elements of monolithic glass, the fibers do
not absorb water and change their dimensions in water. For the same reason, they
are brittle and sensitive to surface damage.
Quartz fibers are similar to glass fibers and are obtained by high-speed stretching
of quartz rods made of (under temperature of about 2200°C) fused quartz crystals
or sand. Original process developed for manufacturing of glass fibers cannot be used

7-

6-

5-

4 4-
0
D
3-

E .%
Fig. 1.7. Stress-strain diagrams for typical fibers of advanced composites.