Crack deflection-penetration at a nanoscale interface of graphene/hBN heterostructure

We investigate crack deflection-penetration behavior at an interface of two elastically dissimilar 2D nanomaterial taking an interface between graphene and hexagonal boron nitride (hBN) as an example test case. Growth of an edge crack from graphene towards hBN and similar growth of crack from hBN towards graphene are considered in two separate cases. Crack deflection-penetration (DP) criterion for continuum study is redefined in terms of cohesive energies of individual solids in this MD study. In case of graphene/hBN heterostructure, crack typically prefers to penetrate either material over deflection when it reaches the interface. Ratios of cohesive energies of interface and material ahead of the crack are 0.67 (when crack in graphene) and 1.0 (when crack in hBN). As these ratios lie in the crack penetration zone of the DP criterion, crack penetration is the only logical choice. However, in some cases slight deflection has been observed. This phenomenon occurs when crack bifurcates into several branches and the mother crack interacts with defects formed at the interface due to lattice constant mismatch.This initial study indicates that at nanoscale crack growth, DP criterion developed for continuum studies cannot be directly applied due to the role of crystallography itself.