Brittle-ductile transition and scatter in fracture toughness of ferritic steels (original) (raw)

Here we analyze a dislocation simulation model for the brittle-to-ductile transition of Ferritic Steels, a typical multiphase material. The crack tip plastic zones are simulated as arrays of discrete dislocations emitted from crack-tip sources and equilibrated against the friction stress due to lattice and obstacles. The crack-tip gets blunted and the emitted dislocation arrays modify the elastic field of the crack. The combined stress field of the crack and the emitted dislocations describe an elasto-plastic crack field. The simulated crack system involves microcracks embedded in the plastic zone of a macrocrack. The inherent scatter in fracture toughness measurements are studied by using a size distribution for microcracks, distributed on the plane of the macrocrack. The scatter in fracture toughness measurements is found to be an effect of the size distribution of microcracks rather than their spatial distribution on the matrix ahead of the crack plane.