Line-defect orientation- And length-dependent strength and toughness in h BN

Abstract

Applying classical molecular dynamics simulations, we report the effects of length (λ) and orientation (θ) of a line-defect on strength and toughness in defective 2D hexagonal boron nitride. Results reveal the existence of a "transition angle,"θ t = 2.47 °, at which both toughness and strength are insensitive to the finite length of the defect in an infinite domain. For θ < θ t, both toughness and strength increase with an increase in defect-length; whereas, for θ > - > θ t, they show the opposite behavior. Examination of the stress-fields shows that θ-dependent variation in stress-localization at the edges of the line-defect and symmetry-breaking of the stress-fields with respect to the defect-axis govern the disparate θ-dependent behavior. For θ < θ t, the intensity of elastic fields at the edges of the line-defect is substantially weakened by the elastic interactions originating from the atoms on the sides of the line-defect. For θ > - > θ t, the stress-intensity at the edges is strongly localized at the opposite sides of the line-defect. The stress-intensity increases asymptotically with the increasing defect-length and reduces the strength and toughness of the defective lattice. The stress-localization, however, saturates at a "saturation angle"of around 60 ° for strength and 30 ° for toughness. Additionally, there exists a critical defect-length λ c = 60 Å, below which there is a strong θ-dependent variation in elastic interactions between the edges, affecting strength and toughness substantially. For λ > - > λ c, the elastic interactions saturate and make both strength and toughness insensitive to the change in the length of the defect.