II.1.10.7 Maximum strain criterion (3D)

The criterion is very similar to maximum stress criterion, except that it is calculated from the mechanical (or equivalent) strain tensor components. The failure index is calculated as follows:

in which the ${ϵ}_{11}^{\text{all}}$, ${ϵ}_{22}^{\text{all}}$ and ${ϵ}_{33}^{\text{all}}$ allowables depend on the sign of the corresponding mechanical strain tensor component. Ply or laminate passes the test if the six following conditions are satisfied:

The reserve factor is calculated as follows:

and the strength ratio is given by

This criterion is referred to as “MaxStrain3D” criterion in FeResPost.

FeResPost proposes a second version of the criterion where the “total” strain tensor $\left\{ϵ\right\}$ is used instead of the mechanical strain tensor $\left\{{ϵ}^{\text{Mech}}\right\}$. This version of the criterion is referred to as “MaxTotalStrain3D” criterion in FeResPost.