The Stiffness Formulation for Strain Equivalence (GPa) is the first tensor displayed for the Anisotropic Elasticity tensor. It is the direct result of the numerical computation and the starting point for all other approximations. This symmetric tensor contains 21 distinct parameters and describes the relationship between the stress and the strain most accurately, see also Wikipedia on Elasticity Tensor.

For the isotropic and the transversely isotropic composite structures being compared here, this tensor looks as follows:

The values obtained for the coefficients defining the relationship between stress and strain can be compared to the matrix for the general elasticity tensor.

The other approximations of this general elasticity tensor are shown when scrolling down in the result file. A large difference between the full tensor and an approximation could mean that:

• The representative volume element is too small, and a larger structure should be used for computations.
• The chosen approximation principally does not hold. For example, the assumption of isotropy for a given structure may be wrong if the stiffness‑tensor entries of its isotropic model deviate markedly from the corresponding entries of the true anisotropic tensor.