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 (E1 and E2), the associated Poisson's ratios (n12, n21), and the in-plane shear modulus G12. The two different Poisson's ratios are defined as follows:
n12, the larger value, gives the strain in the '2' direction associated with a mechanical strain in the '1' direction.
n21, 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.