Strain gradient plasticity theory for modeling JIC of functionally graded steels

Functionally graded ferritic and austenitic steels were produced through electroslag refining by setting the austenitic and carbon steels with appropriate thickness as electrode. Fracture toughness of the specimen in terms of JIC has been studied and modeled regarding the mechanism-based strain gradient plasticity theory. The yield stress of each layer was related to the density of the statistically stored dislocations of that layer and by assuming Holloman relation for the corresponding stress–strain curve, tensile strength and tensile strain of the constituent layers was determined via numerical method. JIC of each layer was related to the corresponding area under stress–strain curve of that layer and finally by applying the rule of mixtures, JIC of functionally graded steels was determined. The obtained results of the proposed model are in good agreement with the experimental ones.