Specially Orthotropic Laminates:

The laminates for which the terms  are zero are called specially orthotropic laminates. It is clear that such laminates do not show coupling between in-plane extensional and shear responses.

Note that the cross-ply, angle-ply and anti-symmetric laminates are specially orthotropic laminates. These laminates by their design have . For cross-ply laminates, the terms  and  are identically zero. Hence, there is no restriction on the lamina thickness for cross-ply laminate to be a specially orthotropic laminate. However, for an angle ply and anti-symmetric laminates the thicknesses of a pair of  and  laminate should be same.

Other specially orthotropic laminates includes the combination of cross-ply and angle ply laminates .

For example,

Quasi-Isotropic Laminates:

A laminate is called quasi-isotropic when its extensional stiffness matrix behaves like an isotropic material. This requires that ,  and . Further, this extensional stiffness matrix is independent of orientation of layers in laminate. This requires a laminate with  equal thickness layers and N equal angles between adjacent fibre orientations. The N equal angles,  between the fibre orientations in this case can be given as

(5.53)

The quasi-isotropic laminate with this construction for N=3, 4 and 6 will have fibre orientations as shown in Figure 5.8.

It should be noted that the isotropy in these laminates is in-plane only. The matrices B and D may not behave like an isotropic material. Hence, such laminates are quasi-isotropic in nature.

Some examples of quasi-isotropic laminate are: , .