DAMAGE MECHANISMS AND FRACTURE BEHAVIOUR OF THERMALLY-AGED DUPLEX STAINLESS STEEL : MODELLING OF THE FRACTURE TOUGHNESS USING LOCAL APPROACH

摘要

The damage mechanisms and fracture behaviour of two duplex stainless steels have been studied afterrnthermal ageing at 325℃ during 30000 hours. The ferrite phase fractures by cleavage whereas austenite lathesrnremain ductile. The heterogeneous nucleation rate of cleavage cracks with strain has been characterised usingrnVorono? cells analysis from surface replicas extracted during tensile test.rnThe observed damage mechanism and fracture behaviour are well described by a model of local approachrnof fracture. The model has been applied to notched tensile specimens using 2D axisymmetric FE calculationsrnwith Castem2000 software developed at CEA. A good prediction of the data scattering and size effect on thernmean strain at failure has been obtained. Finally, 2D calculations have been made to simulate crackrnpropagation in CT specimens tested at room temperature. The simulated J1c and crack propagation resistancernare in agreement with experimental data.