Examination of Cylindrical Shell Theories for Buckling of Carbon Nanotubes

This paper examines the validity and accuracy of cylindrical shell theories in predicting the critical buckling strains of axially loaded single-walled carbon nanotubes (CNTs). The shell theories considered are the Donnell thin shell theory (DST), the Sanders thin shell theory (SST), and the first_order shear deformation (thick) shell theory (FSDST). Molecular dynamic (MD) simulation solutions for armchair and zig-zag CNTs with clamped ends were used as reference results to assess the shell models. The MD simulations were carried out at room temperature to eliminate the thermal effect on the buckling behavior. By adopting Young's modulus of 5.5 TPa, Poisson's ratio of 0.19, and tube thickness of 0.066 nm, it was found that DST is not able to capture the length dependency of the critical buckling strains and thus it should not be used for buckling analysis of CNTs. On the other hand, SST and FSDST are able to predict the critical buckling strains of armchair and zig-zag CNTs reasonably well for all aspect ratios, especially the results produced by the FSDST are found to be closer to the MD simulation results, because it allows for the effect of transverse shear deformation that becomes significant for CNTs with small aspect ratios. Thus, FSDST is recommended as a very suitable and convenient continuum mechanics model for buckling analysis of CNTs. The superior FSDST model is used to generate critical buckling strains of axially loaded single-walled CNT with different boundary conditions. These results should be useful for designers of nanodevices that make use of CNTs as axially loaded members. It is worth noting that for long and moderately long CNTs, the Timoshenko beam model may be used instead due to its simplicity.