A modified normalization method for determining fracture toughness of steel

Normalization method (NM) is a practical method for determining the J–R curves and fracture toughness of steels. There is some concern, however, about the performance of this method on steels with small strain hardening exponent and yield strength owing mainly to the assumption of infinite strain hardening exponent. This paper intends to analytically modify the NM by removing this assumption and incorporating the strain hardening in calculating the blunting corrected crack length. This modification enables the NM to be applied to steels with small strain hardening exponent and yield strength. Experiments are undertaken to verify the modified NM (CNM). A comparison of fracture toughness determined by CNM with that by the unloading compliance method and NM corroborates the improved accuracy of the developed CNM. The paper concludes that the developed CNM overcomes the deficiency of the NM for steels with small strain hardening exponent and yield strength.