Micromechanical Modeling of Crack Propagation with Competing Ductile and Cleavage Failure

Typical engineering metals exhibit a change of the failure mechanism with decreasing temperature. In the range of room temperature a ductile mechanism is observed. Thereby, voids nucleate, grow by plastic deformations of the surrounding matrix and finally the voids coalesce. In contrast in the low temperature regime, cleavage failure occurs, a mechanism which is associated with macroscopically brittle behavior.In the present study the crack initiation and propagation is investigated in the ductile-brittle transition region by means of a microscopic model. The voids in the process zone in front of the crack tip are resolved discretely. Possible void growth in the surrounding plastic zone, which may induce an important shielding effect, is taken into account in a homogenized way by means of the GTN-model. In contrast to comparable studies in the literature not only cleavage crack initiation is addressed but the material degradation by the cleavage mechanism is incorporated explicitly by means of a cohesive zone model. The limit case of small- scale yielding is investigated. This model allows to simulate all stages of crack initiation and propagation at all temperatures. A systematic study of the effects of the model parameters is performed.