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MM: Fachverband Metall- und Materialphysik

MM 36: Topical Session (Symposium MM): Fundamentals of Fracture

MM 36.1: Talk

Wednesday, March 14, 2018, 11:45–12:00, TC 006

Cohesive stress heterogeneities and the transition from intrinsic ductility to brittleness — •Döme Tanguy — University Lyon 1, Villeurbanne, France

The influence of nanoscale cavities on the fracture of the Σ 33 {554}[110] symmetrical tilt grain boundary is studied by atomistic simulations. The crack crystallography is chosen such that dislocation emission is easy. A transition from a ductile behavior of the tip to a brittle one is obtained for a dense (coverage beyond 15% and inter-cavity spacing smaller than 4 nm) distribution of small cavities (sizes in between 1 and 2 nm). Nevertheless, the character of the crack is highly sensitive to the initial position of the tip and a mixture of ductile and brittle responses is found. A heterogeneous cohesive zone model, with parameters extracted from the simulations and enriched with a criterion for plasticity, can explain the simulations and reproduce the transition. Outside this range of small sizes and dense packing, dislocation half loops appear. They constitute, together with regions of low coverage/small cavities, efficient obstacles to brittle cracking. Furthermore, the generic character of the conclusions is evaluated by using the {554} single crystal to determine to which extent the results depend on the details of the core structure vs. the cavity distribution. Paper accepted in Phys. Rev. B.