Fracture mechanics of polycrystalline beryllium oxide nanosheets: A theoretical basis

Polycrystalline beryllium-oxide nanosheets (PBeONS) are today key elements of electronic devices due to their large bandgaps. Their mechanical performance can be tuned by adjusting a number of parameters, such as the number of grains, temperature, and defects in their structure. Nevertheless, even theories can hardly predict their fracture behavior. Herein, we employed Molecular Dynamics Simulation (MDS) to visualize for the first time the effect of the number of grains (4, 9, 16, 25, and 36), temperature (200-900 K), and defects (typical cracks and circular notches with different lengths and dimeters of L/12, L/6, L/3, L/2) on the mechanical properties of square-shaped PBeONS with the length of 300 angstrom (L). It was observed that the failure stress and Young's modulus of PBeONS with 36 grains dropped from 21.7 GPa and 95.77 GPa to the values of 13.85 GPa (ca. 36%) and 54.14 GPa (ca. 43.5%), respectively, with respect the PBeONS with 4 grains in X direction at 300 K. The higher temperatures and large defects increased interatomic distances and weakened the structure, which deteriorated the mechanical strength. Stress intensity factor dropped against temperature, but rose by crack length enlargement showing lower fracture toughness of small cracks.