Page 259 - Plastics Engineering

242 Mechanical Behaviour of Composites

3.11 State whether the following laminates are symmetric or non-symmetric.
(i) [o/w/45/45/w/olT
(ii) P/902/45/ - 45/45/902/01~
(iii) [0/90/45/ - 456/45/9o/o]T
3.12 A plastic composite is made up of three layers of isotropic materials as follows:
Skin layers: Material A, E = 3.5 GN/m2, G = 1.25 GN/m2, u = 0.4
Core layer: Material B, E = 0.6 GN/m2, G = 0.222 GN/m2, u = 0.35.

The skins are each 0.5 mm thick and the core is 0.4 mm thick. If an axial stress of 20 MN/mz,
a transverse stress of 30 MN/m2 and a shear stress of 15 MN/m2 are applied to the composite,
calculate the axial and transverse stresses and strains in each layer.
3.13 A laminate is made up of plies having the following elastic constants
El = 133 GN/m2, E2 = 9 GN/m2, G12 = 5 GN/m2, u12 = 0.31
If the laminate is based on (-60, -30, 0, 30, 60, 90)s and the plies are each 0.2 mm thick,
calculate E,, E,, Gxy and uxy. If a stress of 100 MN/m2 is applied in the x direction, what will
be the axial and lateral strains in the laminate?
3.14 A unidirectional carbon fibrdepoxy composite has the following lay-up
[40, -40,40, -401,
The laminate is 8 mm thick and is subjected to stresses of a, = 80 MN/mz and a, = 40 MN/m2,
determine the strains in the x and y directions. The properties of a single ply are

E1 = 140 GN/m2, E2 = 9 GN/m2, Gl2 = 7 GN/m2 and u12 = 0.3
3.15 A filament wound composite cylindrical pressure vessel has a diameter of 1200 mm and
a wall thickness of 3 mm. It is made up of 10 plies of continuous glass fibres in a polyester resin.
The arrangement of the plies is [03/60/ - 601,. Calculate the axial and hoop strain in the cylinder
when an internal pressure of 3 MN/m2 is applied. The properties of the individual plies are
El = 32 GN/m2, E2 = 8 GN/mz, G12 = 3 GN/mz, u12 = 0.3

3.16 Compare the response of the following laminates to an axial force N, of 40 N/mm. The
plies are each 0.1 mm thick.
(a) [30/ - 301 - 30/30]T
(b) [30/ - 30/30/ - 301~
The properties of the individual plies are

El = 145 GN/m2, E2 = 15 GN/m2, Gl2 = 4 GN/m2, u12 = 0.278
3.17 A unidirectional carbon fibre/PEEK laminate has the stacking sequence [0/35/ - 3%. If
the properties of the individual plies are
E1 = 145 GN/m2, E2 = 15 GN/m2, G12 = 4 GN/m2, u12 = 0.278
If the plies are each 0.1 mm thick, calculate the strains and curvatures if an in-plane stress of
100 MN/m2 is applied.
3.18 A sinfle ply of carbodepoxy composite has the properties listed below and the fibres are
aligned at 25 to the x-direction. If stresses of
a, = 80 MN/m2, a, = 20 MN/m2 and r,, = - 10 MN/m2