Page 238 - Plastics Engineering

Mechanical Behaviour of Composites 22 1

To assist the reader the values of the terms in the matrices are
[3.is; 103 1.16 x 103 B= [I
A = 1.16 x IO3 3.158 x lo3 8 ] N/mm I]
0 996.7
[ 3.670x 10-4 -1.35 x 10-4 0
a = -1.35 x 10-4 3.67 x 10-4 0
0 1.003 x 1 mdN
This type of analysis could also be used for a sandwich structure with solid
sluns and a foamed core. It is simply a matter of using the appropriate values
of El, G12, E2, u12 for the skin and core material. This is illustrated in the
following Example.
Example 3.15 A sandwich moulding is made up of solid skins with a foamed
plastic core. The skins and core may be regarded as isotropic with the following
the properties:

Skin - Material A, El = E2 = 3.5 GN/m2, G12 = 1.25 GN/m2, u12 = 0.4.
Foam Core - Material B, El = E2 = 0.06 GN/m2, Glz = 0.021 GN/m2,
=
~12 0.43.
The skins are each 1 mm thick and the core is 20 mm thick.
If moments of M, = 400 Nm/m and My = 300 Nm/m are applied to the
moulding, calculate the resulting curvatures and the stresses and strains in the
cross-section.
Solution As the skins and core are isotropic, we only need to get the e
values for each:
Skin Foamed Core

- [ 4.16:~ lo3 1.667 x lo3 73.63 31.63 0
Ql = 1.667 x lo3 4.167 x lo3 Q2= 31.63 73.63 0 1
0 1.25 x io3 I - [ o 0 20.98

Assuming as before that there are four layers with the centre line at the
mid-plane of the cross-section, then
ho = -11, hl = -10, h2 = 0, h3 = 10, h4 = 11 mm
As these are only moments applied and the section is symmetric (B = 0) we
only need the D and d matrices. These are given by
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