The Max Strain Criterion identifies composite material failure caused by three possible modes of loading.

The three failure modes are longitudinal failure, transverse failure, and shear failure.

= Value of ε11 at longitudinal tensile failure,

= Value of ε11 at longitudinal compressive failure,

= Value of ε22 at transverse tensile failure,

= Value of ε22 at transverse compressive failure,

= Absolute value of ε12 at longitudinal shear failure,

Longitudinal Failure occurs whenever or

Transverse Failure occurs whenever or

Longitudinal Shear Failure occurs whenever

Failure Index = Max. Absolute Value of

Since the failure index is a simple ratio of strains, the failure load can be computed by simply dividing the applied load by the failure index. For example, consider a composite material subjected to a transverse normal stress of 1 psi. If the computed failure index is 0.0002, the transverse normal stress at failure is (1 psi)/0.0002 = 5000 psi.