Fracture toughness evaluation of interstitial free steel sheet using Essential Work of Fracture (EWF) method

Essential Work of Fracture (EWF) method has been used to evaluate ductile tearing resistance of interstitial-free (IF) steel sheet of 1 mm thickness. Experiments have been done on double edge notched tensile (DENT) specimens with and without fatigue precracking at three different quasi-static ramp rates. The fracture in all cases was flat with maximum specimen necking of 36% of thickness. The estimated crack tip opening angle (CTOA, ψe) was found to be essentially independent of ρ, and also of deformation rate. The critical CTOA (φe) was optically estimated using a precracked DENT specimen. Also, the tearing resistance parameters obtained from EWF tests have been compared with that determined using 3-dimentional Finite Element Modeling (FEM). Results of FEM, along with a chosen traction-separation law, were used in a 3-dimentional Cohesive Zone Model (CZM) for flat fracture to simulate crack growth behavior in the DENT specimens.