Nanofracture of stretched hexagonal boron nitride strip with an edge crack

The tensile fracture behavior in hexagonal boron nitride (h-BN) strip with an introduced zigzag edge crack is investigated by molecular dynamics (MD) using a modified Tersoff potential. The far field remote stress sigma(remote) at crack initiation for various original crack lengths is examined, which shows that Griffith criterion overestimates sigma(remote) for short cracks < 2.5 nm while underestimates that for longer cracks. Thus we propose a modified exponent factor 0.28 for Griffith criterion rather than 0.5. The asymptotic stress field around nano-crack is calculated by MD atomic virial stress theory, comparing with continuum theory of stress intensity factor K and stress concentration factor, which indicates that elastic continuum overestimates local stresses around the crack front as the bond breaking stress remains similar to 54.4 GPa at the tip. The critical energy release rate G(c) at initiation for small cracks < 1.5 nm is also much higher than theoretical toughness G(Ic). Our results provide a clear understanding of the nano-crack fracture in a h-BN strip for the continuum limitation in discrete hexagonal lattices.

Automated summary

The tensile fracture behavior of hexagonal boron nitride (h-BN) strips with zigzag edge cracks was investigated using molecular dynamics (MD) and a modified Tersoff potential. The study found that the Griffith criterion overestimates remote stress for short cracks and underestimates it for longer cracks, proposing a modified exponent factor of 0.28. Results also showed that the elastic continuum overestimates local stresses around crack fronts, with critical energy release rate at initiation for small cracks being significantly higher than theoretical toughness.