For homogenous material or where modulus in tension & compression is same, theoretically both

moduli should match.

But when tensile & compressive moduli are different then ratio of flexural modulus by tensile

modulus can be derived as 4/(1+sqrt(a))2 where a is ratio of modulus in tension by modulus in

compression.

Flexural modulus should be used for comparison of stiffness of materials as it may be average as

stated by Karol & also that it has dependency upon factors such as test sample thickness.

Nevertheless, It may be used for FEA of parts which have flexural mode of deformation to estimate

closer values of deformation.