Effect of Stone-Wales defects on the mechanical behavior of boron nitride nanotubes

The transversely isotropic response of pristine as well as defective boron nitride nanotubes (BNNTs) containing Stone-Wales (SW) defects was comprehensively studied via molecular dynamic simulations with a three-body Tersoff force field. The elastic properties and the failure behavior of BNNTs were studied under the transversely isotropic loading conditions, namely uniaxial tension, twisting moment, in-plane shear and in-plane biaxial tension. The effect of chirality, diameter and SW defect density was taken into consideration. The failure mechanism of BNNTs under each loading condition was explained in detail. Our study reveals that the elastic moduli of zigzag BNNTs are higher than for armchair tubes and decrease as the diameter of the tube increases. The effect of SW defects is found to be higher on the elastic properties of smaller diameter BNNTs than for larger diameter tubes, regardless of chirality. The higher defect density reduces the axial Young's modulus, shear, plane strain bulk and in-plane shear moduli by 11%, 18%, 9% and 7%, respectively. The SW defects affect the (1) longitudinal shear moduli of BNNTs more profoundly irrespective of chirality and (2) the mechanical behavior of zigzag BNNTs stronger compared to armchair ones. It is also found that the mechanical properties of BNNTs are functions of chirality and diameter, especially for small diameter tubes.