Lecture 7

Question 1

What are composite laminates?

Answer 1

Thin sheet constructions are known as laminates are made by stacking unidirectional layers
in predetermined directions (layers are called plies or laminae).

Question 2

What are typical composite laminates? (in terms of number of layers, thickness and arrangement orientations)

Answer 2

Laminates typically have between 4 and 40 layers.

Ply thickness is around 0.125 to 0.25mm for carbon or glass fibre / epoxy prepreg.

Typical lay-ups can be cross ply (90 degrees), angle ply (say 45 degrees) or quasi-isotropic (both 45 and 90 degrees).

Question 3

What would the subscript “s” and “2” suggest in a stacking sequence (0/90)s and (0/90)2?

Answer 3

The order in which the plies are placed through the thickness are symmetric (s) or repeats (2).

Question 4

Give the convention for lay-up and the stacking sequence of a 4 ply laminate with orientations 0, 90, 90, 0 from lower to upper surface.

Answer 4

(0/90)s where s denotes a symmetrical stacking sequence about the mid-plane of the laminate.

Question 5

How strain can be defined in 2D thin-plates?

Answer 5

We can relate strains of all points to their counterpart points on the mid-plane. So with much less number of parameters than a 3D case, we can define strains of all points through the thickness.