Strain rate dependent micromechanical modeling of reinforced polymers with carbon nanotubes

Nano-phased polymers show strain rate dependent mechanical behaviors owing to the nature of polymers. Therefore, in this study a strain rate dependent constitutive equation is developed based on a micromechanics method, to predict the mechanical behavior of nanocomposites under various loading rates. The Goldberg et al. model, as a constitutive equation of polymers, has been used to predict the strain rate dependent mechanical behavior of pure polymers. Then, this model is combined with a micromechanics method (Halpin-Tsai model) to develop a constitutive equation for nano-phased polymers which predicts the stress-strain behavior of carbon nanotube (CNT) reinforced polymers at arbitrary strain rates. Also, contrary to the strain rate dependent behavior of the polymeric matrix, it is assumed that mechanical properties of carbon nanotube particles are not sensitive to loading rates. To verify the proposed model, predicted results are compared with the experimental data of multi-walled carbon nanotube/epoxy (tested in this study) and multi-walled carbon nanotube/polypropylene composites (available experimental data) under various tensile loading rates.