Partners

Abstract:
This study employs molecular dynamics simulations to examine the mechanical properties, fracture toughness, and crack propagation behavior of polycrystalline B6N6, BN, BC3, and C3N4 nanosheets and nanotubes. The effects of the number of grains, temperature, strain rate, edge pre-cracks, and circular-notch defects on Young's modulus, tensile strength, failure strain, and critical fracture toughness is systematically analyzed. Results show that increasing the number of grains reduces both tensile strength and Young's modulus, with BN nanosheets demonstrating the highest overall mechanical performance. Polycrystalline B6N6 exhibits the greatest fracture toughness, followed by BN, BC3, and C3N4, reflecting the role of atomic structure and bonding in energy absorption before failure. Thermal analysis indicates that BN maintains superior mechanical stability at elevated temperatures due to reduced atomic vibrations and stronger B–N bonds. Analyses of pre-cracks and notches reveal that BN is most sensitive to crack propagation, whereas BC3 and C3N4 show crack-insensitive behavior, with failure often initiating at grain boundaries rather than crack tips. Strain rate effects suggest that higher rates enhance fracture toughness by limiting atomic rearrangements and crack growth. For nanotubes, increasing diameter enhances Young's modulus but reduces tensile strength, failure strain, and fracture toughness, with C3N4 nanotubes being most sensitive to temperature. These findings provide detailed insights into the mechanical behavior of polycrystalline nanosheets and nanotubes, guiding the design of nanomaterials with optimized strength, toughness, and thermal stability for advanced applications.

Keywords:
Polycrystalline nanosheetsNanotubesMechanical propertiesFracture toughnessCrack propagation