Atomistic simulations of crack grain-boundary interactions in copper

Grain boundaries (GBs) are important structural features and play an important role in coordinating the plastic deformation of nanocrystalline metals. In the quasi-3D case, the GB structure is determined by three geometric parameters, that is, the GB inclination angle and the crystal orientations of the two forming grains which determine the GB misorientation angle. In this paper, the effects of geometric parameters of the GB on the crack propagation behavior are investigated. Extensive molecular dynamics (MD) simulations are carried out to simulate the uniaxial tension of a series of pre-cracked bicrystal specimens, whose geometric parameters are determined using a novel Sudoku sampling method. Sudoku sampling is based on the unique row and column non-repeat rule of the Sudoku game to achieve uniform sampling in the sampling space, and at the same time to reduce the computational cost. From the MD simulation results five patterns of cracking modes can be discerned, i.e., crack tip blunting, intergranular sliding, transgranular cracking, transgranular sliding and intergranular cracking. It indicates that the GB inclination angle is the most influential factor for the crack propagation behavior, with smaller GB inclination angle corresponding to smaller crack propagation resistance. The GB misorientation angle is second influential, with a large misorientation angle favoring the intergranular crack propagation. This study deepens the understanding of effect of grain boundaries on the fracture behavior in nanocrystalline metals, which guides the development of damage-resistant materials through GB engineering strategy.