Effective Axial Poisson’s Ratio:
           
The effective axial Poisson’s ratio can be determined from the preceding problem definition. Here, we define the effective axial Poisson’s ratio as the ratio of associated lateral strain to the axial strain due to applied load in axial direction. Thus,

(7.215)

From Equation (7.176) we can write

(7.216)

The constants ,  and  and   given from Equation (7.192) can be used in the above equation. Further, one can give the constants and  in terms of   as in Equation (7.197).

(7.217)

Special Case: Fibre and Matrix Materials are Isotropic
           
When both fibre and matrix materials are isotropic in nature, then using either Equation (7.205) or Equation. (7.209), the axial Poisson’s ratio is given as

(7.218)

Comparing this equation with the corresponding equation in strength of materials approach, we see that the first two terms are exactly same. It should be noted that the third term is not a small term.