Dynamic notch fracture toughness assessment of functionally austenitic–martensitic graded steels

Functionally graded steels are a group of functionally graded materials provide an arena so that the maximum possible benefits can be derived from composites including martensite and bainite brittle phases. These phases are created with gradual variation in strength within interface of plane carbon steel and austenitic stainless steel during the fabrication process. In the present research, a functionally austenitic–martensitic graded steel, consists of austenitic and martensitic phases was produced by means of electro slag remelting process and its mechanical behavior under impact loading conditions in the form of crack divider configuration was investigated. Empirical values of the notch fracture toughness J were carried out utilizing load–displacement curve which was recorded in Charpy impact test instrumented by Hopkinson pressure bar (HPB). J-integral is one of the fracture parameters in elastic–plastic fracture mechanics, which can be used to predict the fracture resistance in cracked and notched components. By correlating mean strain energy density criterion and J-integral, and applying the rule of phase mixtures, a mathematical model was developed to predict critical value of J-integral in functionally graded steels with crack divider configuration. Finally, a good compatibility between the experimental results of the dynamic notch fracture toughness and those obtained from the proposed model was observed.