Fracture toughness examination of dual-phase and interstitial free steel using essential work of fracture method

Abstract

Fracture toughness of automotive-grade dual-phase steel (DP450) and interstitial free (IF) steel is determined using essential work of fracture (EWF) methodology. Geometrical constraints of standard fracture toughness tests made the EWF method an alternative for thin sheets. Double edge notched tension (DENT) specimens are used for the EWF tests. The two steels have different mechanical and microstructural properties, which helps test the applicability of the EWF methodology to different materials. The effect of notch-tip radius on the EWF test results is analyzed for both the steels. The sensitivity of fracture toughness to notch-tip radius is not the same for both steels. During the EWF test, the digital image correlation (DIC) technique is used to determine the local strain variation of DENT specimens. The hole expansion ratio is determined for the two steels to compare against the EWF test results. The IF steel, despite lower strength, has better fracture toughness and hole expansion capability against the DP450 steel.