Page 219 - Plastics Engineering

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202 Mechanical Behaviour of Composites

Y12 YXY
so
~1 = -5.14 x ~2 = 8 x y12 = 0.014
These stresses and strains are illustrated in Fig. 3.18.

Global strains Global stresses
0 0.39% -1.2% 0 -0.27%0 0 -150 0 0

-0.39% 0 0 1.2% 0 0.27% 0 0 150 0
v
EX CY rv 0, (3 Y 7
Local strains Local stresses
0 -0.8% 0 -1.4% 0 -26.80 -123 0 -57.5 0

0 0 0.8% 0 1.4% 0 26.8 0 123 0 57.5
€1 €2 r12 01 (32 712
Fig. 3.18 Stresses and strains, Example 3.10

Note that if both plane stresses and moments are applied then the total
stresses will be the algebraic sum of the individual stresses.

3.9 Deformation Behaviour of Laminates

(i) Laminates Made from Unidirectional Plies
The previous analysis has shown that the properties of unidirectional fibre
composites are highly anisotropic. To alleviate this problem, it is common to
build up laminates consisting of stacks of unidirectional lamina arranged at
different orientations. Clearly many permutations are possible in terms of the
numbers of layers (or plies) and the relative orientation of the fibres in each