Micromechanical modeling of viscoelastic properties of carbon nanotube-reinforced polymer composites

A micromechanics model is developed for predicting the linearly viscoelastic properties of carbon nanotube-reinforced polymer composites. By employing the Correspondence Principle in viscoelasticity, the Mori-Tanaka method is extended to the Carson domain. The inversion of the creep compliances from the Carson (transformed) domain to the time (physical) domain is accomplished numerically by using a recently developed multi-precision algorithm. The new micromechanics model is validated by comparing with existing experimental data. By applying the presently developed model, a parametric study for the creep behavior of carbon nanotube-reinforced polymer composites is conducted, with testing temperature, nanotube aspect ratio, nanotube volume fraction and nanotube orientation as the controlling parameters. For composites having unidirectionally aligned nanotubes, numerical results indicate that the increase of the nanotube aspect ratio significantly enhances their axial creep resistance but has insignificant influences on their transverse, shear and plane strain bulk creep compliances. Also, the random orientation of nanotubes provides more effective plane strain bulk creep resistance but less effective axial creep resistance than the aligned orientation does. In addition, the effect of the nanotube orientation on the shear compliances is negligibly small. Furthermore, for composites with aligned or randomly oriented nanotubes, all the compliances are found to decrease monotonically with the increase of the nanotube volume fraction. Finally, the influences of testing temperature on the composite creep compliances (except for the bulk strain compliance) are similar to those on the compliance of the matrix.