Use the damage variable to specify damage to the cohesive material.
Damage to the cohesive material is completely specified by a single scalar quantity 0 ≤ D ≤ 1 referred to as the damage variable. D = 0 indicates an undamaged pristine cohesive material with its full original stiffness. D=1 indicates a completely damaged (failed) cohesive material that has zero stiffness and can no longer support any load.
For all delamination models implemented in Helius PFA, the effect of the scalar damage variable D is always to exert an isotropic reduction in the stiffness of the cohesive material. This is accomplished via the scaling coefficient (1-D), as shown in the following damaged constitutive equations.