Modeling and characterization of damping in carbon nanofiber/polypropylene composites

The objective of this paper is to summarize recent analytical and experimental investigations of the dynamic mechanical properties of carbon nanofiber/polypropylene composites. In this case, the carbon nanofibers are vapor grown carbon fibers (VGCF) which are grown catalytically from gaseous hydrocarbons using metallic catalyst particles. The mechanical damping and storage modulus of these materials are measured by using a Dynamic Mechanical Thermal Analyzer (DMTA). For the analytical model, the elastic–viscoelastic correspondence principle is used to transform the elastic Halpin–Tsai equations to complex form. The model is then validated for the prediction of the damping and stiffness of carbon nanofiber/polypropylene composites having a preferential fiber orientation in the direction of injection. Good agreement between measured and predicted storage values is found over the range of fiber volume fractions investigated. Although predicted and measured damping values are in the same range, the predicted values do not show the measured decrease in damping with increasing fiber volume fraction. Predictions show that composites having very low fiber aspect ratios should have higher damping than those having high fiber aspect ratios, and that the carbon nanofiber aspect ratios of approximately l/d=19 are in the range which yields the highest predicted damping.