II.1.10.4 Maximum stress criterion

The failure index is calculated as follows:

in which the ${\sigma }_{11}^{\text{all}}$ and ${\sigma }_{22}^{\text{all}}$ allowables depend on the sign of ${\sigma }_{11}$ and ${\sigma }_{22}$ respectively. (Generally, tensile and compressive allowables are different for orthotropic materials.) Ply passes the test if the three following conditions are satisfied:

The reserve factor is calculated as follows:

and the strength ratio is given by:

This criterion is referred to as “MaxStress” criterion in FeResPost.