In the tension - tension - compression regime, F takes the form

(2–28)

and S is defined as

(2–29)

If the failure criterion for both i = 1, 2 is satisfied, cracking occurs in the planes perpendicular to principal stresses σ₁ and σ₂. If the failure criterion is satisfied only for i = 1, cracking occurs only in the plane perpendicular to principal stress σ₁.

This domain can also crush. (See Willam and Warnke for details.)