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182 Mechanical Behaviour of Composites
3.6 Deformation Behaviour of a Single Ply or Lamina
The previous section illustrated how to obtain the elastic properties of a uni-
directional lamina. In practice considerably more information may be required
about the behavioural characteristics of a single lamina. To obtain details of the
stresses and strains at various orientations in a single ply the following type of
analysis is required.
(i) Loading on Fibre Axis
Consider the situation of a thin unidirectional lamina under a state of plane
stress as shown in Fig. 3.9. The properties of the lamina are anisotropic so it will
have modulus values of El and E2 in the fibre and transverse directions, respec-
tively. The values of these parameters may be determined as illustrated above.
'1 Global
axes
+ OY
Fig. 3.9 Single thin lamina under plane stress
The direct strains in the global X and Y directions will be given by (see
Appendix C for details)
(3.17)
Ey=-- GY OX (3.18)
1112-
E2 El
