Mechanical response of polycarbonate nanocomposites to high velocity impact

In this study, the mechanical responses of polycarbonate (PC) and PC/multi-walled carbon nanotubes (MWCNTs) to dynamic loadings at low and high velocities impacts were investigated experimentally using an instrumented falling weight impact tester (IFWIT) and a split Hopkinson pressure bar (SHPB), respectively. The results from the IFWIT tests revealed that impact strength, impact failure energy and fracture toughness were dramatically enhanced by the incorporation of a very small amount of the MWCNTs into the PC matrix. The maximum load and the impact failure energy increased by 320% and 350%, respectively, when only 1 wt% MWCNTs was incorporated. The results from the SHPB tests demonstrate that all the materials showed strain-rate sensitivity. The MWCNTs nanocomposites exhibited higher yield stress and energy absorption characteristics compared to the PC matrix material. However, the enhancement by MWCNTs was very limited for the PC containing higher percentage of the filler at higher strain rates. This could be resulted by a thermal-softening effect. In addition, the density of the pure PC and PC/MWCNTs nanocomposite specimens before or after SHPB testing was examined to gain insight into the microstructure changes. The results show that the density decreased significantly after the SPBH tests. With increasing strain rate the density decrease in PC nanocomposite is faster than that in the pure PC. It is believed that more cracks formed in the PC nanocomposite during the SHPB tests, which could result in high energy dissipation.