Numerical Prediction Of Effective Mechanical Properties And Buckling Analysis On Carbon Nanotubes Bundles

Since the discovery of carbon nanotubes, great attention has been attracted due totheir amazing electronic, thermal, mechanical and optical properties. However, it’sdifficult to conduct the experiment at atomic scale. Therefore, some theoreticalmodels have been developed to predict mechanical behaviors of carbon nanotubes. Inthis paper, the effective mechanical behavior, the axial compression buckling behaviorand the radial compression buckling behavior of single-wall carbon nanotube bundles(SCNBs) are analyzed by using the finite element (FE) method and analyticalmethods. The effect of the volume fraction of SCNBs, the number, the length andthe radius of the single-wall carbon nanotube (SCNT), on the effective mechanicalbehavior and the compression buckling behavior, are all examined. Our FEcomputation is base on the commercial softwareABAQUS6.9.Firstly, the effective mechanical behavior of SCNB is investigated by using theFE method. The van der Waals interaction is implemented into the simulations byintroducing a soft matrix among the carbon naotubes. The proposed finite elementmodel is used to simulate the uniaxial tension, torsion and transverse tension tests.The numerical results obtained from this FE model show a good agreement with theanalytical results of the theoretical models. The FE results show that, with the increaseof the number of the SCNT, the axial shear modulus decreases gradually and thentends to be a stable value with the further increase of the number of the SCNT. ThePoisson’s ratio and the other elastic modulus are insensitive to the number of theSCNT. As the radius of the single SCNT increase, the axial Young’s modulus,transverse Young’s modulus and axial transverse shear modulus decrease gradually,transverse Poisson ratio increase gradually. The axial Poisson’s ratio is insensitive tothe radius of the single SCNT. The axial Young’s modulus and axial shear modulusincrease gradually with the increase of the length of the SCNT, and then approaches toa constant affter the length of the SCNT reach400nm. The Poisson’s ratio and theother elastic modulus are insensitive to the length of the SCNT. With the increase ofthe volume fraction of SCNBs, the axial Young’s modulus and transverse Young’smodulus increase gradually, the axial transverse Poisson’s ratios decrease gradually. Secondly，both behaviors of the buckling and the post-buckling of the singleSCNT under axial or radial compressions are analyzed based on characteristic valuebuckle analysis method and Riks method of FE theory. The FE results agree well withthe results obtained from the bucking theory of elastic cylindrical shells and theresults of molecular dynamics (MD). The FE results also show that the axial andradial critical buckling load decrease with the increase of the radius and the length ofthe SCNT.Finally, both behaviors of the buckling and the post-buckling of the single carbonnanotube bundles under axial or radial compressions are simulated. The simulationresult shows that, with the increase of the number of the SCNT and the volumefraction of the SCNBs, the axial and radial critical buckling mean loads of the SCNBsincrease gradually. The radial critical buckling mean loads of SCNBs increase slightlywith the increase of volume fraction. As the length of the SCNBs increase, the axialand radial critical buckling mean loads decrease gradually and then tend to be a stablevalue with the further length increasing. The axial and radial critical buckling meanloads of SCNBs decreases with the increasing radius of SCNBs.