stress intensity factor and crack length calculation using XFEM method

[scorpion09]

Hello everybody
I'm working on crack propagation in mode I using XFEM method.my model is 2D plane stress. i need to calculate SIF at carack tip as crack propagates through material.but abaqus isn't able to calculates SIFs at 2D models. I'm looking for an alternative way to calculate SIfs at crack tip in every increment. also i need to know crack tip location at any time.
does anyone have any idea about this?

thanks in advance.