There are five elastic properties needed to represent the elastic behaviour of a unidirectional laminate under in-plane loading, but only four of these are independent.
The five properties are the modulus of the laminate parallel and perpendicular to the fibre direction (E_{1} and E_{2}), the associated Poisson's ratios (n_{12}, n_{21}), and the in-plane shear modulus G12. The two different Poisson's ratios are defined as follows:
n_{12}, the larger value, gives the strain in the '2' direction associated with a mechanical strain in the '1' direction.
n_{21}, the smaller value, gives the strain in the '1' direction associated with a mechanical strain in the '2' direction.
Q4 A sample of unidirectional CFRP 2 mm thick and 20 mm wide, with elastic properties as above, is subjected to a single tensile load of 20 kN (parallel to the fibre direction). Determine the strains parallel and perpendicular to the fibre direction.