The effect of temperature and topological defects on fracture strength of grain boundaries in single-layer polycrystalline boron-nitride nanosheet

In this paper, molecular dynamic simulations are utilized to investigate the effect of temperature and topological defects on the mechanical response and tensile strength of grain boundaries in single-layer hexagonal boron-nitride (h-BN) nanosheets. Six different cases of grain boundaries are examined including four symmetric and two asymmetric models. We study various types of misorientation angles and defects at different temperatures. The tensile tests of all models are also performed at different strain rates at room temperature. The results clearly show that increasing the misorientation angle of the grain boundary leads to a decreasing tensile strength, elastic modules and strain-at-failure of h-BN nanosheets. The mechanical response of high-angle misorientation grain boundaries were observed to be quite unique under uniaxial tension, since a chain of atoms between two fractured parts was observed even after tensile failure. Increasing the temperature also leads to a decreasing fracture strength and strain-at-failure for all six models. The low-angle misorientation of grain boundaries are more sensitive to variations in the temperature than grain boundaries with high-angle misorientation. The stress-strain curve shows a large drop for low-angles grain boundaries when the temperature elevates from 100K to 300K. In addition, small fluctuations could be observed for all models at high temperature, which does not depend on the misorientation angle of the grain boundary.