Tsai Definition for Poisson's Ratios
The relation between strains, ( 
, and so forth) and stresses (
, and the like) is written as follows:
, and so forth) and stresses ( , and the like) is written as follows:
 | The Material Definition dialog box represents  as Nu. |
In the above expression, 1, 2, and 3 denote the three principal material directions. In a uniaxial tension test pulling in the 1 direction, the ratios of transverse normal strains, 
and 
, to longitudinal normal strain, 
, is given by:
and , to longitudinal normal strain, , is given by:
and 
Also, since the elasticity matrix is symmetric, the following relation between Poisson's ratios and Young's moduli holds:
where i and j take on the values 1, 2, and 3.
Therefore, if 
, then 
, 
and 
.
, then , and .The values you enter for Poisson's ratios must satisfy the requirement that the determinant of the 6 X 6 constitutive equation matrix above is positive.
Return to Poisson's Ratio.