An atomistic K-test framework for general grain boundaries and triclinic single crystals

In the present study, an atomistic K-test framework for the fracture toughness assessment of generally oriented grain boundaries (GBs) (tilt, twist, mixed) and triclinic single crystals is investigated. Boundary conditions for the modelling of cracks along the interfaces of bicrystals are derived based on the 6 th -order Stroh formalism and compared with established approaches. Thereby, especially the oscillations in the relevant field quantities due to mode I loading are critically assessed. It is found that for engineering applications, these oscillations do not compromise the validity of the employed approach since they are confined to a negligibly small region at the crack tip. Next, the 6 th -order Stroh approach is used to investigate crack propagation along GBs under mode I loading. A crack identification and crack tip tracing scheme is included to update the imposed boundary conditions during the simulations. Lastly, a physically-motivated method is discussed and incorporated, which allows for the unambiguous determination of the fracture toughness, including challenging setups such as generally oriented GBs. The so-established K-test setup is validated with a series of numerical examples.