Gurson

I have a question regarding Gurson model. If we have a cube with initial length of unit and initial porosity of 20 percent and compress it hydrostatically in order to have a huge volume change of cube, the void growth equation in Gurson model takes a negative rate and reduces the void volume fraction to zero first and further compressing leads to no further void volume fraction change (remains zero) and no more plastic straining. Now let's load the model in tensile hydrostatic state up to a stress free configuration; the void volume fraction of the model remains zero.