Page 207 - Plastics Engineering

190 Mechanical Behaviour of Composites

The lamina properties are then obtained as:
- 1
S11 = 0.041, E, = 7 E, = 24.26 GN/m2
s11
- 1
S22 = 0.079, E, = g E, = 12.7 GN/m2

- 1
SM = 0.143, GXy = r Gxy = 6.9 GN/m2
s66 -
321 = 0.026, uxY = -E, * S21, up = -Ey . S12,
uxY = 0.627, u,, = -0.328

Alternatively the lamina properties can be calculated from the equations
given above.

- S2 2 - c2 - s2
-
.
s22 = - (s2 - c2 * u12) + - (c2 - 2 - u21) + -
- 0.079,
El E2 G21
1
E, = =- = 12.702
s22

- C2 2 s2 2 2 c2 * s2
s12 = - (c2 * U] - s ) + - (s 9 u2 - c ) + -
*
El E2 G12
u,, = -321 *E,, uxY = 0.627
-
up = 412 E,, up = 0.328
*
In this Example the angle, 8, was set at 25". Fig. 3.1 1 shows the variation of
the moduli and Poisson's Ratio values for all angles between 0" and 90". This
gives an interesting overview of the performance of unidirectional composites
when subjected to off-axis loading.
Example 3.7 A thin unidirectional Kevlar fibre/epoxy composite has the
properties listed below. If the fibres are aligned at 8 to the x-axis, show how