Page 326 - Mechanics Analysis Composite Materials

Chapter 7. Environmmtal. special loading, and manufacturing cffecrs 31 I

Comparison of a,with experimental results of Barnes et al. (1989) for a thermo-
plastic carbon composite is presented in Fig. 7.4 (solid line and dark circles). As
can be seen in this figure, there exists an interval (0 < 4 < 40") within which
the coefficient ax of the angle-ply layer is negative. The same type of behavior is
demonstrated by aramid epoxy angle-ply composites. Comparison of calculation
with the aid of Eqs. (7.22) with experimental results of Strife and Prevo (1979)
is presented in Fig. 7.5. Looking at Figs. 7.4 and 7.5 we can suppose that
supplementing an angle-ply laminate with plies having small thermal elongations in
the x-direction we can synthesize composite materials with zero thermal expansion
in this direction. Such materials are important for space telescopes (Fig. 7.3),
antennas, measuring instruments and other high precision, thermally stable
structures (Hamilton and Patterson, 1993).
Consider laminates with arbitrary structural parameters (see Chapter 5).
Repeating the derivation of Eqs. (5.5) but using the thermoelasticity constitutive
equations, Eqs. (7.17), instead of Eqs. (4.71) we arrive at

These equations should be supplemented with Eqs. (5.15) for transverse shear
forces, i.e.

1o6ff ,I / "c

Fig. 7.5. Calculated (line) and experimental (circles)dependencies of thermal expansion coefficient on the
ply orientation angle for an aramid+poxy =kr$ angle-ply layer.