Page 215 - Plastics Engineering

198 Mechanical Behaviour of Composites

(ii) Loading off Fibre Axis
For the situation where the loading is applied off the fibre axis, then the
above approach involving the Plate Constitutive Equations can be used but it
is necessary to use the transformed stiffness matrix terms 0.
Hence, in the above analysis
[AI = @I * h
103 = @I. h3/12

The use of the Plate Constitutive Equations is illustrated in the following
Examples.
Example 3.9 For the 2 mm thick unidirectional carbon fibre/PEEK
composite described in Example 3.6, calculate the values of the moduli,
Poisson’s Ratio and strains in the global direction when a stress of a, =
50 MN/m2 is applied. You should use
(i) the lamina stiffness and compliance matrix approach and
(ii) the Plate Constitutive Equation approach.

Solution
(i) As shown in Example 3.6, for the loading in Fig. 3.16
I
4.12 10-~ -2.58 x 10-~ -6.24 x 10-~
-2.58 x lo-’ 7.87 x 1.77 x lo-’ m2h4N
-6.24 10-5 1.77 10-5 1.43 10-4
yk

n I

’/

0
Fig. 3.16 Single ply composite subjected to plane stress