Dislocation simulation of brittle-ductile transition in ferritic steels

Abstract

Two-dimensional discrete dislocation simulations of the crack-tip plasticity of a macrocrack-micro-crack system representing the fracture behavior in ferritic steels are presented. The crack-tip plastic zones are represented as arrays of discrete dislocations emitted from crack-tip sources and equilibrated against the friction stress. The dislocation arrays modify the elastic field of the crack; the resulting field describes the elastoplastic crack field. The simulated crack system involves a microcrack in the plastic zone of the macrocrack (elastoplastic stress field). The effects of the crack-tip blunting of the macrocrack are included in the simulations; as dislocations are emitted, the microcrack is kept at a constant distance from the blunted tip of the macrocrack. The brittle-ductile transition (BDT) curve is obtained by simulating the fracture toughness at various temperatures. A consideration of the effects of blunting is found to be critical in predicting the sharp upturn of the BDT curve. The obtained results are compared with existing experimental data and are found to be in reasonable agreement.