Classical laminate theory

Question 1

What void volume fraction is considered good enough in composites made for the aerospace industry?

Answer 1

<1%

Question 2

Why is the transverse rule of mixtures inaccurate for calculating the transverse modulus of a composite?

Answer 2

Non-uniform strain distribution in the matrix.

Question 3

Why is the minor Poisson’s ratio of a unidirectional composite expected to be small?

Answer 3

Contraction direction is fibre dominated and fibres are stiffer than matrix.

Question 4

How many unique compliance coefficients are there in the compliance matrix for an orthotropic, transversely isotropic, unidirectional composite loaded in plane stress?

Answer 4

4

Question 5

What sort of interaction does the composite interaction ratio quantify?

Answer 5

Normal shear or shear normal

Question 6

Why is a unidirectional composite stiffer parallel to the fibres and less stiff (more compliant) perpendicular to the fibres?

Answer 6

Parallel to the fibre direction, the fibres and matrix work in
parallel - there is ‘load sharing’

Perpendicular to the fibre direction, the fibres and matrix work
in series - there is ‘deformation sharing’

Question 7

A quasi isotropic lay-up sequence is isotropic how?

Answer 7

in-plane

Question 8

Why are there higher layer stresses in laminates with multiple angle plies?

Answer 8

Each angle contributes a smaller proportion to the whole, so stress in any given direction is higher.