Damage effective functions reflect the affections related the damage variables to the elastic constants independent of each other of the materials

and its detailed expressions were defined by the geometric features and could be derived from the micro-mechanical damage theories. Firstly

the relationship between the porosity rate and damage variables of the porous materials were given

and then the double scalar damage variables expressions of the isotropic elastic damage were derived. Then

the different influence to damage effective functions by the porosity rate and damage variable in porous media materials was discussed and some valuable conclusions were derived from the point of the relationship between the porosity rate and damage variable. It is shown that the conclusions are beneficial to the further research on the damage mechanics theory.