Line-defect orientation- and length-dependent strength and toughness in hBN

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, 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 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 A, 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.