Ductile - brittle transition of ferritic steels modelled 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 values of stable crack growth occurring before unstable cleavage fracture. Probabilistic modelling is made by coupling the Beremin model for cleavage crack initiation and a model derived from the Gurson potential. In an elementary volume the probability for fracture depends on the probability of both modes of failure. In a larger volume the probability to fracture is expressed in terms of elementary probabilities of fracture through the weakest link theory. Modelling is applied to axisymmetrically notched bars and to CT specimens. The analysis of results shows that the ductile-brittle transition of ferritic steels can be interpreted quantitatively as a competition between both types of damage. (orig.)