How to determine crack length in XFEM analysis

Hi guys,

i am doing crack propagation analysis using XFEM. My model is working fine. i want to know how one can determine the length of the propagated crack against time increment. Is there any built in histroy out put variable with which one can calculate the length of the propagated crack using histroy output or is there any other way for example using pyton scripting. would be my pleasure to hear valuable comments from you guys. 

Alex