Page 255 - Mechanics Analysis Composite Materials

240 Mechanics and analysis of composite materials

h2
smm = (5.44)
k hi '
Ci=l(i)
A mm
Laminates composed of unidirectional plies have special stacking-sequence nota-
tions. For example, notation [0;/+45"/-45"/90~] means that the laminate consists
of 0" layer having two plies, f45" angle-ply layer, and 90" layer also having two
plies. Notation [0"/90"],means that the laminate has five cross-ply layers.

5.4. Quasi-homogeneous laminates
Some typical layers considered in Chapter 4 were actually quasi-homogeneous
laminates (see Sections 4.4, and 4.5),but being composed of a number of identical
plies, they were treated as homogeneous layers. The accuracy of this assumption is
evaluated below.

5.4.I. Laminate composed of identical homogeneous Kayers

Consider a laminate composed of layers with different thicknesses but the same
stiffnesses, Le., such that A:; =A,, for all i = 1,2,3,...k. Then, Eqs. (5.29) and
(5.32) yield

This result coincides with Eqs. (5.33), which means that the laminate consisting of
the layers with the same mechanical properties is a homogeneous laminate (layer)
studied in Section 5.2.

5.4.2. Laminate composed of inhomogeneous orthotropic layers

Let the laminate have the structure [0"/90"],, where p = 1,2,3,... specifies the
number of elementary cross-ply couples of 0" and 90" plies. In Section 4.4, this
laminate was treated as a homogeneous layer with material stiffness coefficients
specified by Eqs. (4.100). Taking 60 = igo = 0.5 in these equations we get

In accordance with Eqs. (5.36), stiffness coefficients of this layer should be