The proposed J-integral calculation technique in the piece-wise linear fatigue crack front has been used investigating SIF in the inhomogeneous cast iron specimens with defect and graphite voids. The influence of crack length and front, size and position of voids on SIF have been investigated and the increase of SIF by 15% has been obtained. Stress-strain state analysis of inhomogeneous cast iron specimens was carried out using FE code ANSYS
