Brittle fracture is known to occur in ductile metals in special gaseous environments. Often, these gases form thin solid films on the metal. Computer simulations were used to study the propagation of cracks coated with thin elastically hard films in a ductile two-dimensional material. It was found that under certain conditions secondary crack nucleation occurred in the simulations and brittle fracture was observed. The dynamics of the crack nucleation and the detailed spatial distribution of local forces were examined. A model has been developed for this new mode of crack nucleation and brittle fracture. The role of the elastically hard film in suppressing dislocation generation and in initiating the secondary crack is discussed. This mode of initiating brittle fracture is entirely different from usual models for gaseous embrittlement.
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