Equivalent nonlinear fracture models for pristine and reconstructed one- and two-atom vacancy defected single wall carbon nanotubes are developed by using the molecular mechanics based models where the initial reconstructed nanotube models are obtained by using molecular dynamic simulations and nonlinear characteristic of the covalent bonds are obtained by using the modified Morse potential. As a result of analyses, it is concluded that fractures of all types of nanotubes are brittle, armchair nanotubes are stiffer than zigzag nanotubes and vacancy defects significantly affect the mechanical behavior of nanotubes. In brief, fracture stress and strain values of pristine armchair nanotubes are respectively 30% and 32% larger than those of pristine zigzag nanotubes, and predicted failure stress and strain values of vacancy defected nanotubes are respectively 27% and 52% smaller than those of pristine ones. It is shown that large deformation and nonlinear geometric effects are important on fracture behavior of nanotubes. Comparisons are made with the failure stress and strain results reported in literature that show good agreement with our results. (C) 2013 Elsevier Ltd. All rights reserved.