DUCTILE-BRITTLE TRANSITION OF FERRITIC STEELS MODELED BY THE LOCAL APPROACH TO FRACTURE

Tensile tests on axisymmetrically notched specimens were performed at various temperatures in the ductile-brittle transition region to study the initiation of fracture. Fracture toughness tests on CT specimens were also carried out in the same region to investigate the critical v alues of stable crack growth occurring before unstable cleavage fractu re. Probabilistic modelling is made by coupling the Beremin model for cleavage crack initiation and a model derived from the Gurson potentia l. In an elementary volume the probability for fracture depends on the probability of both modes of failure. In a larger volume the probabil ity to fracture is expressed in terms of elementary probabilities of f racture through the weakest link theory. Modelling is applied to axisy mmetrically notched bars and to CT specimens. The analysis of results shows that the ductile-brittle transition of ferritic steels can be in terpreted quantitatively as a competition between both types of damage .