The Introduction of Shear Modification to Gurson Model

I have been asked questions about how the shear modification was introduced to the Gurson model. I was also asked to compare my modification (see Xue L., Constitutive modeling of void shearing effect in ductile fracture of porous materials, Engineering Fracture Mechanics, 2008, 75(11):3343-3366) to John Hutchinson's modification (Nahshon, K., Hutchinson, J.W., Modification of the Gurson model for shear failure. European Journal of Mechanics A/Solids, 2008, 27:1-17).